ocfs2: fix crash caused by stale lvb with fsdlm plugin
diff mbox

Message ID 1481275846-6604-1-git-send-email-zren@suse.com
State New
Headers show

Commit Message

Zhen Ren Dec. 9, 2016, 9:30 a.m. UTC
The crash happens rather often when we reset some cluster
nodes while nodes contend fiercely to do truncate and append.

The crash backtrace is below:
"
[  245.197849] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover_grant 1 locks on 971 resources
[  245.197859] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover 9 generation 5 done: 4 ms
[  245.198379] ocfs2: Begin replay journal (node 318952601, slot 2) on device (253,18)
[  247.272338] ocfs2: End replay journal (node 318952601, slot 2) on device (253,18)
[  247.547084] ocfs2: Beginning quota recovery on device (253,18) for slot 2
[  247.683263] ocfs2: Finishing quota recovery on device (253,18) for slot 2
[  247.833022] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: bug expression: le64_to_cpu(fe->i_size) != i_size_read(inode)
[  247.833029] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: Inode 290321, inode i_size = 732 != di i_size = 937, i_flags = 0x1
[  247.833074] ------------[ cut here ]------------
[  247.833077] kernel BUG at /usr/src/linux/fs/ocfs2/file.c:470!
[  247.833079] invalid opcode: 0000 [#1] SMP
[  247.833081] Modules linked in: ocfs2_stack_user(OEN) ocfs2(OEN) ocfs2_nodemanager ocfs2_stackglue(OEN) quota_tree dlm(OEN) configfs fuse sd_mod    iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi af_packet iscsi_ibft iscsi_boot_sysfs softdog xfs libcrc32c ppdev parport_pc pcspkr parport      joydev virtio_balloon virtio_net i2c_piix4 acpi_cpufreq button processor ext4 crc16 jbd2 mbcache ata_generic cirrus virtio_blk ata_piix               drm_kms_helper ahci syscopyarea libahci sysfillrect sysimgblt fb_sys_fops ttm floppy libata drm virtio_pci virtio_ring uhci_hcd virtio ehci_hcd       usbcore serio_raw usb_common sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua scsi_mod autofs4
[  247.833107] Supported: No, Unsupported modules are loaded
[  247.833110] CPU: 1 PID: 30154 Comm: truncate Tainted: G           OE   N  4.4.21-69-default #1
[  247.833111] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
[  247.833112] task: ffff88004ff6d240 ti: ffff880074e68000 task.ti: ffff880074e68000
[  247.833113] RIP: 0010:[<ffffffffa05c8c30>]  [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
[  247.833151] RSP: 0018:ffff880074e6bd50  EFLAGS: 00010282
[  247.833152] RAX: 0000000000000074 RBX: 000000000000029e RCX: 0000000000000000
[  247.833153] RDX: 0000000000000001 RSI: 0000000000000246 RDI: 0000000000000246
[  247.833154] RBP: ffff880074e6bda8 R08: 000000003675dc7a R09: ffffffff82013414
[  247.833155] R10: 0000000000034c50 R11: 0000000000000000 R12: ffff88003aab3448
[  247.833156] R13: 00000000000002dc R14: 0000000000046e11 R15: 0000000000000020
[  247.833157] FS:  00007f839f965700(0000) GS:ffff88007fc80000(0000) knlGS:0000000000000000
[  247.833158] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  247.833159] CR2: 00007f839f97e000 CR3: 0000000036723000 CR4: 00000000000006e0
[  247.833164] Stack:
[  247.833165]  00000000000003a9 0000000000000001 ffff880060554000 ffff88004fcaf000
[  247.833167]  ffff88003aa7b090 1000000000000000 ffff88003aab3448 ffff880074e6beb0
[  247.833169]  0000000000000001 0000000000002068 0000000000000020 0000000000000000
[  247.833171] Call Trace:
[  247.833208]  [<ffffffffa05cb1a8>] ocfs2_setattr+0x698/0xa90 [ocfs2]
[  247.833225]  [<ffffffff8121587e>] notify_change+0x1ae/0x380
[  247.833242]  [<ffffffff811f8bfe>] do_truncate+0x5e/0x90
[  247.833246]  [<ffffffff811f8f58>] do_sys_ftruncate.constprop.11+0x108/0x160
[  247.833257]  [<ffffffff815e142e>] entry_SYSCALL_64_fastpath+0x12/0x6d
[  247.834724] DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x6d
[  247.834725]
[  247.834726] Leftover inexact backtrace:

[  247.834728] Code: 24 28 ba d6 01 00 00 48 c7 c6 30 43 62 a0 8b 41 2c 89 44 24 08 48 8b 41 20 48 c7 c1 78 a3 62 a0 48 89 04 24 31 c0 e8 a0 97 f9 ff <0f> 0b 3d 00 fe ff ff 0f 84 ab fd ff ff 83 f8 fc 0f 84 a2 fd ff
[  247.834748] RIP  [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
[  247.834774]  RSP <ffff880074e6bd50>
"

It's because ocfs2_inode_lock() get us stale LVB in which the i_size is not
equal to the disk i_size. We mistakenly trust the LVB because the underlaying
fsdlm dlm_lock() doesn't set lkb_sbflags with DLM_SBF_VALNOTVALID properly for
us. But, why?

The current code tries to downconvert lock without DLM_LKF_VALBLK
flag to tell o2cb don't update RSB's LVB if it's a PR->NULL conversion,
even if the lock resource type needs LVB. This is not the right way for fsdlm.

The fsdlm plugin behaves different on DLM_LKF_VALBLK, it depends on
DLM_LKF_VALBLK to decide if we care about the LVB in the LKB. If DLM_LKF_VALBLK
is not set, fsdlm will skip recovering RSB's LVB from this lkb and set the right
DLM_SBF_VALNOTVALID appropriately when node failure happens.

The following diagram briefly illustrates how this crash happens:

RSB1 is inode metadata lock resource with LOCK_TYPE_USES_LVB;

The 1st round:

             Node1                                    Node2
RSB1: PR
                                                  RSB1(master): NULL->EX
ocfs2_downconvert_lock(PR->NULL, set_lvb==0)
  ocfs2_dlm_lock(no DLM_LKF_VALBLK)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

dlm_lock(no DLM_LKF_VALBLK)
  convert_lock(overwrite lkb->lkb_exflags
               with no DLM_LKF_VALBLK)

RSB1: NULL                                        RSB1: EX
                                                  reset Node2
dlm_recover_rsbs()
  recover_lvb()

/* The LVB is not trustable if the node with EX fails and
 * no lock >= PR is left. We should set RSB_VALNOTVALID for RSB1.
 */

 if(!(kb_exflags & DLM_LKF_VALBLK)) /* This means we miss the chance to
           return;                   * to invalid the LVB here.
                                     */

The 2nd round:

         Node 1                                Node2
RSB1(become master from recovery)

ocfs2_setattr()
  ocfs2_inode_lock(NULL->EX)
    /* dlm_lock() return the stale lvb without setting DLM_SBF_VALNOTVALID */
    ocfs2_meta_lvb_is_trustable() return 1 /* so we don't refresh inode from disk */
  ocfs2_truncate_file()
      mlog_bug_on_msg(disk isize != i_size_read(inode))  /* crash! */

The fix is quite straightforward. We keep to set DLM_LKF_VALBLK flag for dlm_lock()
if the lock resource type needs LVB and the fsdlm plugin is uesed.

Signed-off-by: Eric Ren <zren@suse.com>
---
 fs/ocfs2/dlmglue.c   | 10 ++++++++++
 fs/ocfs2/stackglue.c |  6 ++++++
 fs/ocfs2/stackglue.h |  3 +++
 3 files changed, 19 insertions(+)

Comments

Gang He Dec. 12, 2016, 2:56 a.m. UTC | #1
Hi Eric,

Looks good for me.
Just one suggestion, 
please monitor if the LVB sharing mechanism in the cluster still works well in the normal scenario, 
to avoid any performance decrease regression problem.

Reviewed-by: Gang He <ghe@suse.com>

Thanks
Gang


>>> 
> The crash happens rather often when we reset some cluster
> nodes while nodes contend fiercely to do truncate and append.
> 
> The crash backtrace is below:
> "
> [  245.197849] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover_grant 1 
> locks on 971 resources
> [  245.197859] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover 9 
> generation 5 done: 4 ms
> [  245.198379] ocfs2: Begin replay journal (node 318952601, slot 2) on 
> device (253,18)
> [  247.272338] ocfs2: End replay journal (node 318952601, slot 2) on device 
> (253,18)
> [  247.547084] ocfs2: Beginning quota recovery on device (253,18) for slot 2
> [  247.683263] ocfs2: Finishing quota recovery on device (253,18) for slot 2
> [  247.833022] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: bug 
> expression: le64_to_cpu(fe->i_size) != i_size_read(inode)
> [  247.833029] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: Inode 
> 290321, inode i_size = 732 != di i_size = 937, i_flags = 0x1
> [  247.833074] ------------[ cut here ]------------
> [  247.833077] kernel BUG at /usr/src/linux/fs/ocfs2/file.c:470!
> [  247.833079] invalid opcode: 0000 [#1] SMP
> [  247.833081] Modules linked in: ocfs2_stack_user(OEN) ocfs2(OEN) 
> ocfs2_nodemanager ocfs2_stackglue(OEN) quota_tree dlm(OEN) configfs fuse 
> sd_mod    iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi af_packet 
> iscsi_ibft iscsi_boot_sysfs softdog xfs libcrc32c ppdev parport_pc pcspkr 
> parport      joydev virtio_balloon virtio_net i2c_piix4 acpi_cpufreq button 
> processor ext4 crc16 jbd2 mbcache ata_generic cirrus virtio_blk ata_piix      
>          drm_kms_helper ahci syscopyarea libahci sysfillrect sysimgblt 
> fb_sys_fops ttm floppy libata drm virtio_pci virtio_ring uhci_hcd virtio 
> ehci_hcd       usbcore serio_raw usb_common sg dm_multipath dm_mod 
> scsi_dh_rdac scsi_dh_emc scsi_dh_alua scsi_mod autofs4
> [  247.833107] Supported: No, Unsupported modules are loaded
> [  247.833110] CPU: 1 PID: 30154 Comm: truncate Tainted: G           OE   N  
> 4.4.21-69-default #1
> [  247.833111] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
> rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
> [  247.833112] task: ffff88004ff6d240 ti: ffff880074e68000 task.ti: 
> ffff880074e68000
> [  247.833113] RIP: 0010:[<ffffffffa05c8c30>]  [<ffffffffa05c8c30>] 
> ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
> [  247.833151] RSP: 0018:ffff880074e6bd50  EFLAGS: 00010282
> [  247.833152] RAX: 0000000000000074 RBX: 000000000000029e RCX: 
> 0000000000000000
> [  247.833153] RDX: 0000000000000001 RSI: 0000000000000246 RDI: 
> 0000000000000246
> [  247.833154] RBP: ffff880074e6bda8 R08: 000000003675dc7a R09: 
> ffffffff82013414
> [  247.833155] R10: 0000000000034c50 R11: 0000000000000000 R12: 
> ffff88003aab3448
> [  247.833156] R13: 00000000000002dc R14: 0000000000046e11 R15: 
> 0000000000000020
> [  247.833157] FS:  00007f839f965700(0000) GS:ffff88007fc80000(0000) 
> knlGS:0000000000000000
> [  247.833158] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [  247.833159] CR2: 00007f839f97e000 CR3: 0000000036723000 CR4: 
> 00000000000006e0
> [  247.833164] Stack:
> [  247.833165]  00000000000003a9 0000000000000001 ffff880060554000 
> ffff88004fcaf000
> [  247.833167]  ffff88003aa7b090 1000000000000000 ffff88003aab3448 
> ffff880074e6beb0
> [  247.833169]  0000000000000001 0000000000002068 0000000000000020 
> 0000000000000000
> [  247.833171] Call Trace:
> [  247.833208]  [<ffffffffa05cb1a8>] ocfs2_setattr+0x698/0xa90 [ocfs2]
> [  247.833225]  [<ffffffff8121587e>] notify_change+0x1ae/0x380
> [  247.833242]  [<ffffffff811f8bfe>] do_truncate+0x5e/0x90
> [  247.833246]  [<ffffffff811f8f58>] do_sys_ftruncate.constprop.11+0x108/0x160
> [  247.833257]  [<ffffffff815e142e>] entry_SYSCALL_64_fastpath+0x12/0x6d
> [  247.834724] DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x6d
> [  247.834725]
> [  247.834726] Leftover inexact backtrace:
> 
> [  247.834728] Code: 24 28 ba d6 01 00 00 48 c7 c6 30 43 62 a0 8b 41 2c 89 
> 44 24 08 48 8b 41 20 48 c7 c1 78 a3 62 a0 48 89 04 24 31 c0 e8 a0 97 f9 ff <0f> 
> 0b 3d 00 fe ff ff 0f 84 ab fd ff ff 83 f8 fc 0f 84 a2 fd ff
> [  247.834748] RIP  [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 
> [ocfs2]
> [  247.834774]  RSP <ffff880074e6bd50>
> "
> 
> It's because ocfs2_inode_lock() get us stale LVB in which the i_size is not
> equal to the disk i_size. We mistakenly trust the LVB because the 
> underlaying
> fsdlm dlm_lock() doesn't set lkb_sbflags with DLM_SBF_VALNOTVALID properly 
> for
> us. But, why?
> 
> The current code tries to downconvert lock without DLM_LKF_VALBLK
> flag to tell o2cb don't update RSB's LVB if it's a PR->NULL conversion,
> even if the lock resource type needs LVB. This is not the right way for 
> fsdlm.
> 
> The fsdlm plugin behaves different on DLM_LKF_VALBLK, it depends on
> DLM_LKF_VALBLK to decide if we care about the LVB in the LKB. If 
> DLM_LKF_VALBLK
> is not set, fsdlm will skip recovering RSB's LVB from this lkb and set the 
> right
> DLM_SBF_VALNOTVALID appropriately when node failure happens.
> 
> The following diagram briefly illustrates how this crash happens:
> 
> RSB1 is inode metadata lock resource with LOCK_TYPE_USES_LVB;
> 
> The 1st round:
> 
>              Node1                                    Node2
> RSB1: PR
>                                                   RSB1(master): NULL->EX
> ocfs2_downconvert_lock(PR->NULL, set_lvb==0)
>   ocfs2_dlm_lock(no DLM_LKF_VALBLK)
> 
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 
> dlm_lock(no DLM_LKF_VALBLK)
>   convert_lock(overwrite lkb->lkb_exflags
>                with no DLM_LKF_VALBLK)
> 
> RSB1: NULL                                        RSB1: EX
>                                                   reset Node2
> dlm_recover_rsbs()
>   recover_lvb()
> 
> /* The LVB is not trustable if the node with EX fails and
>  * no lock >= PR is left. We should set RSB_VALNOTVALID for RSB1.
>  */
> 
>  if(!(kb_exflags & DLM_LKF_VALBLK)) /* This means we miss the chance to
>            return;                   * to invalid the LVB here.
>                                      */
> 
> The 2nd round:
> 
>          Node 1                                Node2
> RSB1(become master from recovery)
> 
> ocfs2_setattr()
>   ocfs2_inode_lock(NULL->EX)
>     /* dlm_lock() return the stale lvb without setting DLM_SBF_VALNOTVALID 
> */
>     ocfs2_meta_lvb_is_trustable() return 1 /* so we don't refresh inode from 
> disk */
>   ocfs2_truncate_file()
>       mlog_bug_on_msg(disk isize != i_size_read(inode))  /* crash! */
> 
> The fix is quite straightforward. We keep to set DLM_LKF_VALBLK flag for 
> dlm_lock()
> if the lock resource type needs LVB and the fsdlm plugin is uesed.
> 
> Signed-off-by: Eric Ren <zren@suse.com>
> ---
>  fs/ocfs2/dlmglue.c   | 10 ++++++++++
>  fs/ocfs2/stackglue.c |  6 ++++++
>  fs/ocfs2/stackglue.h |  3 +++
>  3 files changed, 19 insertions(+)
> 
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 83d576f..77d1632 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -3303,6 +3303,16 @@ static int ocfs2_downconvert_lock(struct ocfs2_super 
> *osb,
>  	mlog(ML_BASTS, "lockres %s, level %d => %d\n", lockres->l_name,
>  	     lockres->l_level, new_level);
>  
> +	/*
> +	 * On DLM_LKF_VALBLK, fsdlm behaves differently with o2cb. It always
> +	 * expects DLM_LKF_VALBLK being set if the LKB has LVB, so that
> +	 * we can recover correctly from node failure. Otherwise, we may get
> +	 * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
> +	 */
> +	if (!ocfs2_is_o2cb_active() &&
> +	    lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
> +		lvb = 1;
> +
>  	if (lvb)
>  		dlm_flags |= DLM_LKF_VALBLK;
>  
> diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
> index 52c07346b..8203590 100644
> --- a/fs/ocfs2/stackglue.c
> +++ b/fs/ocfs2/stackglue.c
> @@ -48,6 +48,12 @@ static char ocfs2_hb_ctl_path[OCFS2_MAX_HB_CTL_PATH] = 
> "/sbin/ocfs2_hb_ctl";
>   */
>  static struct ocfs2_stack_plugin *active_stack;
>  
> +inline int ocfs2_is_o2cb_active(void)
> +{
> +	return !strcmp(active_stack->sp_name, OCFS2_STACK_PLUGIN_O2CB);
> +}
> +EXPORT_SYMBOL_GPL(ocfs2_is_o2cb_active);
> +
>  static struct ocfs2_stack_plugin *ocfs2_stack_lookup(const char *name)
>  {
>  	struct ocfs2_stack_plugin *p;
> diff --git a/fs/ocfs2/stackglue.h b/fs/ocfs2/stackglue.h
> index f2dce10..e3036e1 100644
> --- a/fs/ocfs2/stackglue.h
> +++ b/fs/ocfs2/stackglue.h
> @@ -298,6 +298,9 @@ void ocfs2_stack_glue_set_max_proto_version(struct 
> ocfs2_protocol_version *max_p
>  int ocfs2_stack_glue_register(struct ocfs2_stack_plugin *plugin);
>  void ocfs2_stack_glue_unregister(struct ocfs2_stack_plugin *plugin);
>  
> +/* In ocfs2_downconvert_lock(), we need to know which stack we are using */
> +int ocfs2_is_o2cb_active(void);
> +
>  extern struct kset *ocfs2_kset;
>  
>  #endif  /* STACKGLUE_H */
> -- 
> 2.6.6
Zhen Ren Dec. 12, 2016, 3:23 a.m. UTC | #2
Hi Gang,

On 12/12/2016 10:56 AM, Gang He wrote:
> Hi Eric,
>
> Looks good for me.
> Just one suggestion,
> please monitor if the LVB sharing mechanism in the cluster still works well in the normal scenario,
> to avoid any performance decrease regression problem.
Thanks for your review. I have done the testing as you suggested, and it works
as expected.

Thanks,
Eric
>
> Reviewed-by: Gang He <ghe@suse.com>
>
> Thanks
> Gang
>
>
>> The crash happens rather often when we reset some cluster
>> nodes while nodes contend fiercely to do truncate and append.
>>
>> The crash backtrace is below:
>> "
>> [  245.197849] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover_grant 1
>> locks on 971 resources
>> [  245.197859] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover 9
>> generation 5 done: 4 ms
>> [  245.198379] ocfs2: Begin replay journal (node 318952601, slot 2) on
>> device (253,18)
>> [  247.272338] ocfs2: End replay journal (node 318952601, slot 2) on device
>> (253,18)
>> [  247.547084] ocfs2: Beginning quota recovery on device (253,18) for slot 2
>> [  247.683263] ocfs2: Finishing quota recovery on device (253,18) for slot 2
>> [  247.833022] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: bug
>> expression: le64_to_cpu(fe->i_size) != i_size_read(inode)
>> [  247.833029] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: Inode
>> 290321, inode i_size = 732 != di i_size = 937, i_flags = 0x1
>> [  247.833074] ------------[ cut here ]------------
>> [  247.833077] kernel BUG at /usr/src/linux/fs/ocfs2/file.c:470!
>> [  247.833079] invalid opcode: 0000 [#1] SMP
>> [  247.833081] Modules linked in: ocfs2_stack_user(OEN) ocfs2(OEN)
>> ocfs2_nodemanager ocfs2_stackglue(OEN) quota_tree dlm(OEN) configfs fuse
>> sd_mod    iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi af_packet
>> iscsi_ibft iscsi_boot_sysfs softdog xfs libcrc32c ppdev parport_pc pcspkr
>> parport      joydev virtio_balloon virtio_net i2c_piix4 acpi_cpufreq button
>> processor ext4 crc16 jbd2 mbcache ata_generic cirrus virtio_blk ata_piix
>>           drm_kms_helper ahci syscopyarea libahci sysfillrect sysimgblt
>> fb_sys_fops ttm floppy libata drm virtio_pci virtio_ring uhci_hcd virtio
>> ehci_hcd       usbcore serio_raw usb_common sg dm_multipath dm_mod
>> scsi_dh_rdac scsi_dh_emc scsi_dh_alua scsi_mod autofs4
>> [  247.833107] Supported: No, Unsupported modules are loaded
>> [  247.833110] CPU: 1 PID: 30154 Comm: truncate Tainted: G           OE   N
>> 4.4.21-69-default #1
>> [  247.833111] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
>> [  247.833112] task: ffff88004ff6d240 ti: ffff880074e68000 task.ti:
>> ffff880074e68000
>> [  247.833113] RIP: 0010:[<ffffffffa05c8c30>]  [<ffffffffa05c8c30>]
>> ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
>> [  247.833151] RSP: 0018:ffff880074e6bd50  EFLAGS: 00010282
>> [  247.833152] RAX: 0000000000000074 RBX: 000000000000029e RCX:
>> 0000000000000000
>> [  247.833153] RDX: 0000000000000001 RSI: 0000000000000246 RDI:
>> 0000000000000246
>> [  247.833154] RBP: ffff880074e6bda8 R08: 000000003675dc7a R09:
>> ffffffff82013414
>> [  247.833155] R10: 0000000000034c50 R11: 0000000000000000 R12:
>> ffff88003aab3448
>> [  247.833156] R13: 00000000000002dc R14: 0000000000046e11 R15:
>> 0000000000000020
>> [  247.833157] FS:  00007f839f965700(0000) GS:ffff88007fc80000(0000)
>> knlGS:0000000000000000
>> [  247.833158] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [  247.833159] CR2: 00007f839f97e000 CR3: 0000000036723000 CR4:
>> 00000000000006e0
>> [  247.833164] Stack:
>> [  247.833165]  00000000000003a9 0000000000000001 ffff880060554000
>> ffff88004fcaf000
>> [  247.833167]  ffff88003aa7b090 1000000000000000 ffff88003aab3448
>> ffff880074e6beb0
>> [  247.833169]  0000000000000001 0000000000002068 0000000000000020
>> 0000000000000000
>> [  247.833171] Call Trace:
>> [  247.833208]  [<ffffffffa05cb1a8>] ocfs2_setattr+0x698/0xa90 [ocfs2]
>> [  247.833225]  [<ffffffff8121587e>] notify_change+0x1ae/0x380
>> [  247.833242]  [<ffffffff811f8bfe>] do_truncate+0x5e/0x90
>> [  247.833246]  [<ffffffff811f8f58>] do_sys_ftruncate.constprop.11+0x108/0x160
>> [  247.833257]  [<ffffffff815e142e>] entry_SYSCALL_64_fastpath+0x12/0x6d
>> [  247.834724] DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x6d
>> [  247.834725]
>> [  247.834726] Leftover inexact backtrace:
>>
>> [  247.834728] Code: 24 28 ba d6 01 00 00 48 c7 c6 30 43 62 a0 8b 41 2c 89
>> 44 24 08 48 8b 41 20 48 c7 c1 78 a3 62 a0 48 89 04 24 31 c0 e8 a0 97 f9 ff <0f>
>> 0b 3d 00 fe ff ff 0f 84 ab fd ff ff 83 f8 fc 0f 84 a2 fd ff
>> [  247.834748] RIP  [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0
>> [ocfs2]
>> [  247.834774]  RSP <ffff880074e6bd50>
>> "
>>
>> It's because ocfs2_inode_lock() get us stale LVB in which the i_size is not
>> equal to the disk i_size. We mistakenly trust the LVB because the
>> underlaying
>> fsdlm dlm_lock() doesn't set lkb_sbflags with DLM_SBF_VALNOTVALID properly
>> for
>> us. But, why?
>>
>> The current code tries to downconvert lock without DLM_LKF_VALBLK
>> flag to tell o2cb don't update RSB's LVB if it's a PR->NULL conversion,
>> even if the lock resource type needs LVB. This is not the right way for
>> fsdlm.
>>
>> The fsdlm plugin behaves different on DLM_LKF_VALBLK, it depends on
>> DLM_LKF_VALBLK to decide if we care about the LVB in the LKB. If
>> DLM_LKF_VALBLK
>> is not set, fsdlm will skip recovering RSB's LVB from this lkb and set the
>> right
>> DLM_SBF_VALNOTVALID appropriately when node failure happens.
>>
>> The following diagram briefly illustrates how this crash happens:
>>
>> RSB1 is inode metadata lock resource with LOCK_TYPE_USES_LVB;
>>
>> The 1st round:
>>
>>               Node1                                    Node2
>> RSB1: PR
>>                                                    RSB1(master): NULL->EX
>> ocfs2_downconvert_lock(PR->NULL, set_lvb==0)
>>    ocfs2_dlm_lock(no DLM_LKF_VALBLK)
>>
>> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>>
>> dlm_lock(no DLM_LKF_VALBLK)
>>    convert_lock(overwrite lkb->lkb_exflags
>>                 with no DLM_LKF_VALBLK)
>>
>> RSB1: NULL                                        RSB1: EX
>>                                                    reset Node2
>> dlm_recover_rsbs()
>>    recover_lvb()
>>
>> /* The LVB is not trustable if the node with EX fails and
>>   * no lock >= PR is left. We should set RSB_VALNOTVALID for RSB1.
>>   */
>>
>>   if(!(kb_exflags & DLM_LKF_VALBLK)) /* This means we miss the chance to
>>             return;                   * to invalid the LVB here.
>>                                       */
>>
>> The 2nd round:
>>
>>           Node 1                                Node2
>> RSB1(become master from recovery)
>>
>> ocfs2_setattr()
>>    ocfs2_inode_lock(NULL->EX)
>>      /* dlm_lock() return the stale lvb without setting DLM_SBF_VALNOTVALID
>> */
>>      ocfs2_meta_lvb_is_trustable() return 1 /* so we don't refresh inode from
>> disk */
>>    ocfs2_truncate_file()
>>        mlog_bug_on_msg(disk isize != i_size_read(inode))  /* crash! */
>>
>> The fix is quite straightforward. We keep to set DLM_LKF_VALBLK flag for
>> dlm_lock()
>> if the lock resource type needs LVB and the fsdlm plugin is uesed.
>>
>> Signed-off-by: Eric Ren <zren@suse.com>
>> ---
>>   fs/ocfs2/dlmglue.c   | 10 ++++++++++
>>   fs/ocfs2/stackglue.c |  6 ++++++
>>   fs/ocfs2/stackglue.h |  3 +++
>>   3 files changed, 19 insertions(+)
>>
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index 83d576f..77d1632 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -3303,6 +3303,16 @@ static int ocfs2_downconvert_lock(struct ocfs2_super
>> *osb,
>>   	mlog(ML_BASTS, "lockres %s, level %d => %d\n", lockres->l_name,
>>   	     lockres->l_level, new_level);
>>   
>> +	/*
>> +	 * On DLM_LKF_VALBLK, fsdlm behaves differently with o2cb. It always
>> +	 * expects DLM_LKF_VALBLK being set if the LKB has LVB, so that
>> +	 * we can recover correctly from node failure. Otherwise, we may get
>> +	 * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
>> +	 */
>> +	if (!ocfs2_is_o2cb_active() &&
>> +	    lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
>> +		lvb = 1;
>> +
>>   	if (lvb)
>>   		dlm_flags |= DLM_LKF_VALBLK;
>>   
>> diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
>> index 52c07346b..8203590 100644
>> --- a/fs/ocfs2/stackglue.c
>> +++ b/fs/ocfs2/stackglue.c
>> @@ -48,6 +48,12 @@ static char ocfs2_hb_ctl_path[OCFS2_MAX_HB_CTL_PATH] =
>> "/sbin/ocfs2_hb_ctl";
>>    */
>>   static struct ocfs2_stack_plugin *active_stack;
>>   
>> +inline int ocfs2_is_o2cb_active(void)
>> +{
>> +	return !strcmp(active_stack->sp_name, OCFS2_STACK_PLUGIN_O2CB);
>> +}
>> +EXPORT_SYMBOL_GPL(ocfs2_is_o2cb_active);
>> +
>>   static struct ocfs2_stack_plugin *ocfs2_stack_lookup(const char *name)
>>   {
>>   	struct ocfs2_stack_plugin *p;
>> diff --git a/fs/ocfs2/stackglue.h b/fs/ocfs2/stackglue.h
>> index f2dce10..e3036e1 100644
>> --- a/fs/ocfs2/stackglue.h
>> +++ b/fs/ocfs2/stackglue.h
>> @@ -298,6 +298,9 @@ void ocfs2_stack_glue_set_max_proto_version(struct
>> ocfs2_protocol_version *max_p
>>   int ocfs2_stack_glue_register(struct ocfs2_stack_plugin *plugin);
>>   void ocfs2_stack_glue_unregister(struct ocfs2_stack_plugin *plugin);
>>   
>> +/* In ocfs2_downconvert_lock(), we need to know which stack we are using */
>> +int ocfs2_is_o2cb_active(void);
>> +
>>   extern struct kset *ocfs2_kset;
>>   
>>   #endif  /* STACKGLUE_H */
>> -- 
>> 2.6.6
> _______________________________________________
> Ocfs2-devel mailing list
> Ocfs2-devel@oss.oracle.com
> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
>
Joseph Qi Dec. 15, 2016, 1:46 a.m. UTC | #3
In you description, this issue can only happen in case of stack user +

fsdlm.

So I feel we'd better to make stack user and o2cb behaves the same,

other than treat it as a special case.


Thanks,

Joseph

On 16/12/9 17:30, Eric Ren wrote:
> The crash happens rather often when we reset some cluster
> nodes while nodes contend fiercely to do truncate and append.
>
> The crash backtrace is below:
> "
> [  245.197849] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover_grant 1 locks on 971 resources
> [  245.197859] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover 9 generation 5 done: 4 ms
> [  245.198379] ocfs2: Begin replay journal (node 318952601, slot 2) on device (253,18)
> [  247.272338] ocfs2: End replay journal (node 318952601, slot 2) on device (253,18)
> [  247.547084] ocfs2: Beginning quota recovery on device (253,18) for slot 2
> [  247.683263] ocfs2: Finishing quota recovery on device (253,18) for slot 2
> [  247.833022] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: bug expression: le64_to_cpu(fe->i_size) != i_size_read(inode)
> [  247.833029] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: Inode 290321, inode i_size = 732 != di i_size = 937, i_flags = 0x1
> [  247.833074] ------------[ cut here ]------------
> [  247.833077] kernel BUG at /usr/src/linux/fs/ocfs2/file.c:470!
> [  247.833079] invalid opcode: 0000 [#1] SMP
> [  247.833081] Modules linked in: ocfs2_stack_user(OEN) ocfs2(OEN) ocfs2_nodemanager ocfs2_stackglue(OEN) quota_tree dlm(OEN) configfs fuse sd_mod    iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi af_packet iscsi_ibft iscsi_boot_sysfs softdog xfs libcrc32c ppdev parport_pc pcspkr parport      joydev virtio_balloon virtio_net i2c_piix4 acpi_cpufreq button processor ext4 crc16 jbd2 mbcache ata_generic cirrus virtio_blk ata_piix               drm_kms_helper ahci syscopyarea libahci sysfillrect sysimgblt fb_sys_fops ttm floppy libata drm virtio_pci virtio_ring uhci_hcd virtio ehci_hcd       usbcore serio_raw usb_common sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua scsi_mod autofs4
> [  247.833107] Supported: No, Unsupported modules are loaded
> [  247.833110] CPU: 1 PID: 30154 Comm: truncate Tainted: G           OE   N  4.4.21-69-default #1
> [  247.833111] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
> [  247.833112] task: ffff88004ff6d240 ti: ffff880074e68000 task.ti: ffff880074e68000
> [  247.833113] RIP: 0010:[<ffffffffa05c8c30>]  [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
> [  247.833151] RSP: 0018:ffff880074e6bd50  EFLAGS: 00010282
> [  247.833152] RAX: 0000000000000074 RBX: 000000000000029e RCX: 0000000000000000
> [  247.833153] RDX: 0000000000000001 RSI: 0000000000000246 RDI: 0000000000000246
> [  247.833154] RBP: ffff880074e6bda8 R08: 000000003675dc7a R09: ffffffff82013414
> [  247.833155] R10: 0000000000034c50 R11: 0000000000000000 R12: ffff88003aab3448
> [  247.833156] R13: 00000000000002dc R14: 0000000000046e11 R15: 0000000000000020
> [  247.833157] FS:  00007f839f965700(0000) GS:ffff88007fc80000(0000) knlGS:0000000000000000
> [  247.833158] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [  247.833159] CR2: 00007f839f97e000 CR3: 0000000036723000 CR4: 00000000000006e0
> [  247.833164] Stack:
> [  247.833165]  00000000000003a9 0000000000000001 ffff880060554000 ffff88004fcaf000
> [  247.833167]  ffff88003aa7b090 1000000000000000 ffff88003aab3448 ffff880074e6beb0
> [  247.833169]  0000000000000001 0000000000002068 0000000000000020 0000000000000000
> [  247.833171] Call Trace:
> [  247.833208]  [<ffffffffa05cb1a8>] ocfs2_setattr+0x698/0xa90 [ocfs2]
> [  247.833225]  [<ffffffff8121587e>] notify_change+0x1ae/0x380
> [  247.833242]  [<ffffffff811f8bfe>] do_truncate+0x5e/0x90
> [  247.833246]  [<ffffffff811f8f58>] do_sys_ftruncate.constprop.11+0x108/0x160
> [  247.833257]  [<ffffffff815e142e>] entry_SYSCALL_64_fastpath+0x12/0x6d
> [  247.834724] DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x6d
> [  247.834725]
> [  247.834726] Leftover inexact backtrace:
>
> [  247.834728] Code: 24 28 ba d6 01 00 00 48 c7 c6 30 43 62 a0 8b 41 2c 89 44 24 08 48 8b 41 20 48 c7 c1 78 a3 62 a0 48 89 04 24 31 c0 e8 a0 97 f9 ff <0f> 0b 3d 00 fe ff ff 0f 84 ab fd ff ff 83 f8 fc 0f 84 a2 fd ff
> [  247.834748] RIP  [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
> [  247.834774]  RSP <ffff880074e6bd50>
> "
>
> It's because ocfs2_inode_lock() get us stale LVB in which the i_size is not
> equal to the disk i_size. We mistakenly trust the LVB because the underlaying
> fsdlm dlm_lock() doesn't set lkb_sbflags with DLM_SBF_VALNOTVALID properly for
> us. But, why?
>
> The current code tries to downconvert lock without DLM_LKF_VALBLK
> flag to tell o2cb don't update RSB's LVB if it's a PR->NULL conversion,
> even if the lock resource type needs LVB. This is not the right way for fsdlm.
>
> The fsdlm plugin behaves different on DLM_LKF_VALBLK, it depends on
> DLM_LKF_VALBLK to decide if we care about the LVB in the LKB. If DLM_LKF_VALBLK
> is not set, fsdlm will skip recovering RSB's LVB from this lkb and set the right
> DLM_SBF_VALNOTVALID appropriately when node failure happens.
>
> The following diagram briefly illustrates how this crash happens:
>
> RSB1 is inode metadata lock resource with LOCK_TYPE_USES_LVB;
>
> The 1st round:
>
>               Node1                                    Node2
> RSB1: PR
>                                                    RSB1(master): NULL->EX
> ocfs2_downconvert_lock(PR->NULL, set_lvb==0)
>    ocfs2_dlm_lock(no DLM_LKF_VALBLK)
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>
> dlm_lock(no DLM_LKF_VALBLK)
>    convert_lock(overwrite lkb->lkb_exflags
>                 with no DLM_LKF_VALBLK)
>
> RSB1: NULL                                        RSB1: EX
>                                                    reset Node2
> dlm_recover_rsbs()
>    recover_lvb()
>
> /* The LVB is not trustable if the node with EX fails and
>   * no lock >= PR is left. We should set RSB_VALNOTVALID for RSB1.
>   */
>
>   if(!(kb_exflags & DLM_LKF_VALBLK)) /* This means we miss the chance to
>             return;                   * to invalid the LVB here.
>                                       */
>
> The 2nd round:
>
>           Node 1                                Node2
> RSB1(become master from recovery)
>
> ocfs2_setattr()
>    ocfs2_inode_lock(NULL->EX)
>      /* dlm_lock() return the stale lvb without setting DLM_SBF_VALNOTVALID */
>      ocfs2_meta_lvb_is_trustable() return 1 /* so we don't refresh inode from disk */
>    ocfs2_truncate_file()
>        mlog_bug_on_msg(disk isize != i_size_read(inode))  /* crash! */
>
> The fix is quite straightforward. We keep to set DLM_LKF_VALBLK flag for dlm_lock()
> if the lock resource type needs LVB and the fsdlm plugin is uesed.
>
> Signed-off-by: Eric Ren <zren@suse.com>
> ---
>   fs/ocfs2/dlmglue.c   | 10 ++++++++++
>   fs/ocfs2/stackglue.c |  6 ++++++
>   fs/ocfs2/stackglue.h |  3 +++
>   3 files changed, 19 insertions(+)
>
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 83d576f..77d1632 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -3303,6 +3303,16 @@ static int ocfs2_downconvert_lock(struct ocfs2_super *osb,
>   	mlog(ML_BASTS, "lockres %s, level %d => %d\n", lockres->l_name,
>   	     lockres->l_level, new_level);
>   
> +	/*
> +	 * On DLM_LKF_VALBLK, fsdlm behaves differently with o2cb. It always
> +	 * expects DLM_LKF_VALBLK being set if the LKB has LVB, so that
> +	 * we can recover correctly from node failure. Otherwise, we may get
> +	 * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
> +	 */
> +	if (!ocfs2_is_o2cb_active() &&
> +	    lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
> +		lvb = 1;
> +
>   	if (lvb)
>   		dlm_flags |= DLM_LKF_VALBLK;
>   
> diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
> index 52c07346b..8203590 100644
> --- a/fs/ocfs2/stackglue.c
> +++ b/fs/ocfs2/stackglue.c
> @@ -48,6 +48,12 @@ static char ocfs2_hb_ctl_path[OCFS2_MAX_HB_CTL_PATH] = "/sbin/ocfs2_hb_ctl";
>    */
>   static struct ocfs2_stack_plugin *active_stack;
>   
> +inline int ocfs2_is_o2cb_active(void)
> +{
> +	return !strcmp(active_stack->sp_name, OCFS2_STACK_PLUGIN_O2CB);
> +}
> +EXPORT_SYMBOL_GPL(ocfs2_is_o2cb_active);
> +
>   static struct ocfs2_stack_plugin *ocfs2_stack_lookup(const char *name)
>   {
>   	struct ocfs2_stack_plugin *p;
> diff --git a/fs/ocfs2/stackglue.h b/fs/ocfs2/stackglue.h
> index f2dce10..e3036e1 100644
> --- a/fs/ocfs2/stackglue.h
> +++ b/fs/ocfs2/stackglue.h
> @@ -298,6 +298,9 @@ void ocfs2_stack_glue_set_max_proto_version(struct ocfs2_protocol_version *max_p
>   int ocfs2_stack_glue_register(struct ocfs2_stack_plugin *plugin);
>   void ocfs2_stack_glue_unregister(struct ocfs2_stack_plugin *plugin);
>   
> +/* In ocfs2_downconvert_lock(), we need to know which stack we are using */
> +int ocfs2_is_o2cb_active(void);
> +
>   extern struct kset *ocfs2_kset;
>   
>   #endif  /* STACKGLUE_H */
Zhen Ren Dec. 15, 2016, 2:27 a.m. UTC | #4
Hi,

On 12/15/2016 09:46 AM, Joseph Qi wrote:
> In you description, this issue can only happen in case of stack user +
>
> fsdlm.
Yes.
>
> So I feel we'd better to make stack user and o2cb behaves the same,
>
> other than treat it as a special case.
Yes, I agree. But, actually, there is nothing wrong with fsdlm. I think o2cb does some tricks
with  DLM_LKF_VALBLK flag in such a special case where down conversion is PR->NULL.

I'd like to see this quick and small fix to be merged at this moment, because this issue is 
little emergency for us.
Anyway, we can supersede this one easily if someone familiar with o2cb works out a patch for 
o2cb in the future.

Does this sounds good to you?

Thanks,
Eric
>
>
> Thanks,
>
> Joseph
>
> On 16/12/9 17:30, Eric Ren wrote:
>> The crash happens rather often when we reset some cluster
>> nodes while nodes contend fiercely to do truncate and append.
>>
>> The crash backtrace is below:
>> "
>> [  245.197849] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover_grant 1 locks on 971 
>> resources
>> [  245.197859] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover 9 generation 5 done: 4 ms
>> [  245.198379] ocfs2: Begin replay journal (node 318952601, slot 2) on device (253,18)
>> [  247.272338] ocfs2: End replay journal (node 318952601, slot 2) on device (253,18)
>> [  247.547084] ocfs2: Beginning quota recovery on device (253,18) for slot 2
>> [  247.683263] ocfs2: Finishing quota recovery on device (253,18) for slot 2
>> [  247.833022] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: bug expression: 
>> le64_to_cpu(fe->i_size) != i_size_read(inode)
>> [  247.833029] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: Inode 290321, inode 
>> i_size = 732 != di i_size = 937, i_flags = 0x1
>> [  247.833074] ------------[ cut here ]------------
>> [  247.833077] kernel BUG at /usr/src/linux/fs/ocfs2/file.c:470!
>> [  247.833079] invalid opcode: 0000 [#1] SMP
>> [  247.833081] Modules linked in: ocfs2_stack_user(OEN) ocfs2(OEN) ocfs2_nodemanager 
>> ocfs2_stackglue(OEN) quota_tree dlm(OEN) configfs fuse sd_mod    iscsi_tcp libiscsi_tcp 
>> libiscsi scsi_transport_iscsi af_packet iscsi_ibft iscsi_boot_sysfs softdog xfs libcrc32c 
>> ppdev parport_pc pcspkr parport joydev virtio_balloon virtio_net i2c_piix4 acpi_cpufreq 
>> button processor ext4 crc16 jbd2 mbcache ata_generic cirrus virtio_blk 
>> ata_piix               drm_kms_helper ahci syscopyarea libahci sysfillrect sysimgblt 
>> fb_sys_fops ttm floppy libata drm virtio_pci virtio_ring uhci_hcd virtio ehci_hcd       
>> usbcore serio_raw usb_common sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua 
>> scsi_mod autofs4
>> [  247.833107] Supported: No, Unsupported modules are loaded
>> [  247.833110] CPU: 1 PID: 30154 Comm: truncate Tainted: G           OE   N  
>> 4.4.21-69-default #1
>> [  247.833111] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
>> rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
>> [  247.833112] task: ffff88004ff6d240 ti: ffff880074e68000 task.ti: ffff880074e68000
>> [  247.833113] RIP: 0010:[<ffffffffa05c8c30>] [<ffffffffa05c8c30>] 
>> ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
>> [  247.833151] RSP: 0018:ffff880074e6bd50  EFLAGS: 00010282
>> [  247.833152] RAX: 0000000000000074 RBX: 000000000000029e RCX: 0000000000000000
>> [  247.833153] RDX: 0000000000000001 RSI: 0000000000000246 RDI: 0000000000000246
>> [  247.833154] RBP: ffff880074e6bda8 R08: 000000003675dc7a R09: ffffffff82013414
>> [  247.833155] R10: 0000000000034c50 R11: 0000000000000000 R12: ffff88003aab3448
>> [  247.833156] R13: 00000000000002dc R14: 0000000000046e11 R15: 0000000000000020
>> [  247.833157] FS:  00007f839f965700(0000) GS:ffff88007fc80000(0000) knlGS:0000000000000000
>> [  247.833158] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [  247.833159] CR2: 00007f839f97e000 CR3: 0000000036723000 CR4: 00000000000006e0
>> [  247.833164] Stack:
>> [  247.833165]  00000000000003a9 0000000000000001 ffff880060554000 ffff88004fcaf000
>> [  247.833167]  ffff88003aa7b090 1000000000000000 ffff88003aab3448 ffff880074e6beb0
>> [  247.833169]  0000000000000001 0000000000002068 0000000000000020 0000000000000000
>> [  247.833171] Call Trace:
>> [  247.833208]  [<ffffffffa05cb1a8>] ocfs2_setattr+0x698/0xa90 [ocfs2]
>> [  247.833225]  [<ffffffff8121587e>] notify_change+0x1ae/0x380
>> [  247.833242]  [<ffffffff811f8bfe>] do_truncate+0x5e/0x90
>> [  247.833246]  [<ffffffff811f8f58>] do_sys_ftruncate.constprop.11+0x108/0x160
>> [  247.833257]  [<ffffffff815e142e>] entry_SYSCALL_64_fastpath+0x12/0x6d
>> [  247.834724] DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x6d
>> [  247.834725]
>> [  247.834726] Leftover inexact backtrace:
>>
>> [  247.834728] Code: 24 28 ba d6 01 00 00 48 c7 c6 30 43 62 a0 8b 41 2c 89 44 24 08 48 8b 
>> 41 20 48 c7 c1 78 a3 62 a0 48 89 04 24 31 c0 e8 a0 97 f9 ff <0f> 0b 3d 00 fe ff ff 0f 84 
>> ab fd ff ff 83 f8 fc 0f 84 a2 fd ff
>> [  247.834748] RIP  [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
>> [  247.834774]  RSP <ffff880074e6bd50>
>> "
>>
>> It's because ocfs2_inode_lock() get us stale LVB in which the i_size is not
>> equal to the disk i_size. We mistakenly trust the LVB because the underlaying
>> fsdlm dlm_lock() doesn't set lkb_sbflags with DLM_SBF_VALNOTVALID properly for
>> us. But, why?
>>
>> The current code tries to downconvert lock without DLM_LKF_VALBLK
>> flag to tell o2cb don't update RSB's LVB if it's a PR->NULL conversion,
>> even if the lock resource type needs LVB. This is not the right way for fsdlm.
>>
>> The fsdlm plugin behaves different on DLM_LKF_VALBLK, it depends on
>> DLM_LKF_VALBLK to decide if we care about the LVB in the LKB. If DLM_LKF_VALBLK
>> is not set, fsdlm will skip recovering RSB's LVB from this lkb and set the right
>> DLM_SBF_VALNOTVALID appropriately when node failure happens.
>>
>> The following diagram briefly illustrates how this crash happens:
>>
>> RSB1 is inode metadata lock resource with LOCK_TYPE_USES_LVB;
>>
>> The 1st round:
>>
>>               Node1                                    Node2
>> RSB1: PR
>>                                                    RSB1(master): NULL->EX
>> ocfs2_downconvert_lock(PR->NULL, set_lvb==0)
>>    ocfs2_dlm_lock(no DLM_LKF_VALBLK)
>>
>> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>>
>> dlm_lock(no DLM_LKF_VALBLK)
>>    convert_lock(overwrite lkb->lkb_exflags
>>                 with no DLM_LKF_VALBLK)
>>
>> RSB1: NULL                                        RSB1: EX
>>                                                    reset Node2
>> dlm_recover_rsbs()
>>    recover_lvb()
>>
>> /* The LVB is not trustable if the node with EX fails and
>>   * no lock >= PR is left. We should set RSB_VALNOTVALID for RSB1.
>>   */
>>
>>   if(!(kb_exflags & DLM_LKF_VALBLK)) /* This means we miss the chance to
>>             return;                   * to invalid the LVB here.
>>                                       */
>>
>> The 2nd round:
>>
>>           Node 1                                Node2
>> RSB1(become master from recovery)
>>
>> ocfs2_setattr()
>>    ocfs2_inode_lock(NULL->EX)
>>      /* dlm_lock() return the stale lvb without setting DLM_SBF_VALNOTVALID */
>>      ocfs2_meta_lvb_is_trustable() return 1 /* so we don't refresh inode from disk */
>>    ocfs2_truncate_file()
>>        mlog_bug_on_msg(disk isize != i_size_read(inode))  /* crash! */
>>
>> The fix is quite straightforward. We keep to set DLM_LKF_VALBLK flag for dlm_lock()
>> if the lock resource type needs LVB and the fsdlm plugin is uesed.
>>
>> Signed-off-by: Eric Ren <zren@suse.com>
>> ---
>>   fs/ocfs2/dlmglue.c   | 10 ++++++++++
>>   fs/ocfs2/stackglue.c |  6 ++++++
>>   fs/ocfs2/stackglue.h |  3 +++
>>   3 files changed, 19 insertions(+)
>>
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index 83d576f..77d1632 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -3303,6 +3303,16 @@ static int ocfs2_downconvert_lock(struct ocfs2_super *osb,
>>       mlog(ML_BASTS, "lockres %s, level %d => %d\n", lockres->l_name,
>>            lockres->l_level, new_level);
>>   +    /*
>> +     * On DLM_LKF_VALBLK, fsdlm behaves differently with o2cb. It always
>> +     * expects DLM_LKF_VALBLK being set if the LKB has LVB, so that
>> +     * we can recover correctly from node failure. Otherwise, we may get
>> +     * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
>> +     */
>> +    if (!ocfs2_is_o2cb_active() &&
>> +        lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
>> +        lvb = 1;
>> +
>>       if (lvb)
>>           dlm_flags |= DLM_LKF_VALBLK;
>>   diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
>> index 52c07346b..8203590 100644
>> --- a/fs/ocfs2/stackglue.c
>> +++ b/fs/ocfs2/stackglue.c
>> @@ -48,6 +48,12 @@ static char ocfs2_hb_ctl_path[OCFS2_MAX_HB_CTL_PATH] = 
>> "/sbin/ocfs2_hb_ctl";
>>    */
>>   static struct ocfs2_stack_plugin *active_stack;
>>   +inline int ocfs2_is_o2cb_active(void)
>> +{
>> +    return !strcmp(active_stack->sp_name, OCFS2_STACK_PLUGIN_O2CB);
>> +}
>> +EXPORT_SYMBOL_GPL(ocfs2_is_o2cb_active);
>> +
>>   static struct ocfs2_stack_plugin *ocfs2_stack_lookup(const char *name)
>>   {
>>       struct ocfs2_stack_plugin *p;
>> diff --git a/fs/ocfs2/stackglue.h b/fs/ocfs2/stackglue.h
>> index f2dce10..e3036e1 100644
>> --- a/fs/ocfs2/stackglue.h
>> +++ b/fs/ocfs2/stackglue.h
>> @@ -298,6 +298,9 @@ void ocfs2_stack_glue_set_max_proto_version(struct 
>> ocfs2_protocol_version *max_p
>>   int ocfs2_stack_glue_register(struct ocfs2_stack_plugin *plugin);
>>   void ocfs2_stack_glue_unregister(struct ocfs2_stack_plugin *plugin);
>>   +/* In ocfs2_downconvert_lock(), we need to know which stack we are using */
>> +int ocfs2_is_o2cb_active(void);
>> +
>>   extern struct kset *ocfs2_kset;
>>     #endif  /* STACKGLUE_H */
>
>
Joseph Qi Dec. 19, 2016, 9:55 a.m. UTC | #5
On 16/12/15 10:27, Eric Ren wrote:
> Hi,
>
> On 12/15/2016 09:46 AM, Joseph Qi wrote:
>> In you description, this issue can only happen in case of stack user +
>>
>> fsdlm.
> Yes.
>>
>> So I feel we'd better to make stack user and o2cb behaves the same,
>>
>> other than treat it as a special case.
> Yes, I agree. But, actually, there is nothing wrong with fsdlm. I 
> think o2cb does some tricks
> with  DLM_LKF_VALBLK flag in such a special case where down conversion 
> is PR->NULL.
>
> I'd like to see this quick and small fix to be merged at this moment, 
> because this issue is little emergency for us.
> Anyway, we can supersede this one easily if someone familiar with o2cb 
> works out a patch for o2cb in the future.
>
> Does this sounds good to you?

Fine.
Reviewed-by: Joseph Qi <jiangqi903@gmail.com>

Thanks,
Joseph
>
> Thanks,
> Eric
>>
>>
>> Thanks,
>>
>> Joseph
>>
>> On 16/12/9 17:30, Eric Ren wrote:
>>> The crash happens rather often when we reset some cluster
>>> nodes while nodes contend fiercely to do truncate and append.
>>>
>>> The crash backtrace is below:
>>> "
>>> [  245.197849] dlm: C21CBDA5E0774F4BA5A9D4F317717495: 
>>> dlm_recover_grant 1 locks on 971 resources
>>> [  245.197859] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover 9 
>>> generation 5 done: 4 ms
>>> [  245.198379] ocfs2: Begin replay journal (node 318952601, slot 2) 
>>> on device (253,18)
>>> [  247.272338] ocfs2: End replay journal (node 318952601, slot 2) on 
>>> device (253,18)
>>> [  247.547084] ocfs2: Beginning quota recovery on device (253,18) 
>>> for slot 2
>>> [  247.683263] ocfs2: Finishing quota recovery on device (253,18) 
>>> for slot 2
>>> [  247.833022] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: bug 
>>> expression: le64_to_cpu(fe->i_size) != i_size_read(inode)
>>> [  247.833029] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: 
>>> Inode 290321, inode i_size = 732 != di i_size = 937, i_flags = 0x1
>>> [  247.833074] ------------[ cut here ]------------
>>> [  247.833077] kernel BUG at /usr/src/linux/fs/ocfs2/file.c:470!
>>> [  247.833079] invalid opcode: 0000 [#1] SMP
>>> [  247.833081] Modules linked in: ocfs2_stack_user(OEN) ocfs2(OEN) 
>>> ocfs2_nodemanager ocfs2_stackglue(OEN) quota_tree dlm(OEN) configfs 
>>> fuse sd_mod    iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi 
>>> af_packet iscsi_ibft iscsi_boot_sysfs softdog xfs libcrc32c ppdev 
>>> parport_pc pcspkr parport joydev virtio_balloon virtio_net i2c_piix4 
>>> acpi_cpufreq button processor ext4 crc16 jbd2 mbcache ata_generic 
>>> cirrus virtio_blk ata_piix drm_kms_helper ahci syscopyarea libahci 
>>> sysfillrect sysimgblt fb_sys_fops ttm floppy libata drm virtio_pci 
>>> virtio_ring uhci_hcd virtio ehci_hcd       usbcore serio_raw 
>>> usb_common sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc 
>>> scsi_dh_alua scsi_mod autofs4
>>> [  247.833107] Supported: No, Unsupported modules are loaded
>>> [  247.833110] CPU: 1 PID: 30154 Comm: truncate Tainted: G           
>>> OE   N  4.4.21-69-default #1
>>> [  247.833111] Hardware name: QEMU Standard PC (i440FX + PIIX, 
>>> 1996), BIOS rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
>>> [  247.833112] task: ffff88004ff6d240 ti: ffff880074e68000 task.ti: 
>>> ffff880074e68000
>>> [  247.833113] RIP: 0010:[<ffffffffa05c8c30>] [<ffffffffa05c8c30>] 
>>> ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
>>> [  247.833151] RSP: 0018:ffff880074e6bd50  EFLAGS: 00010282
>>> [  247.833152] RAX: 0000000000000074 RBX: 000000000000029e RCX: 
>>> 0000000000000000
>>> [  247.833153] RDX: 0000000000000001 RSI: 0000000000000246 RDI: 
>>> 0000000000000246
>>> [  247.833154] RBP: ffff880074e6bda8 R08: 000000003675dc7a R09: 
>>> ffffffff82013414
>>> [  247.833155] R10: 0000000000034c50 R11: 0000000000000000 R12: 
>>> ffff88003aab3448
>>> [  247.833156] R13: 00000000000002dc R14: 0000000000046e11 R15: 
>>> 0000000000000020
>>> [  247.833157] FS:  00007f839f965700(0000) GS:ffff88007fc80000(0000) 
>>> knlGS:0000000000000000
>>> [  247.833158] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>> [  247.833159] CR2: 00007f839f97e000 CR3: 0000000036723000 CR4: 
>>> 00000000000006e0
>>> [  247.833164] Stack:
>>> [  247.833165]  00000000000003a9 0000000000000001 ffff880060554000 
>>> ffff88004fcaf000
>>> [  247.833167]  ffff88003aa7b090 1000000000000000 ffff88003aab3448 
>>> ffff880074e6beb0
>>> [  247.833169]  0000000000000001 0000000000002068 0000000000000020 
>>> 0000000000000000
>>> [  247.833171] Call Trace:
>>> [  247.833208]  [<ffffffffa05cb1a8>] ocfs2_setattr+0x698/0xa90 [ocfs2]
>>> [  247.833225]  [<ffffffff8121587e>] notify_change+0x1ae/0x380
>>> [  247.833242]  [<ffffffff811f8bfe>] do_truncate+0x5e/0x90
>>> [  247.833246]  [<ffffffff811f8f58>] 
>>> do_sys_ftruncate.constprop.11+0x108/0x160
>>> [  247.833257]  [<ffffffff815e142e>] 
>>> entry_SYSCALL_64_fastpath+0x12/0x6d
>>> [  247.834724] DWARF2 unwinder stuck at 
>>> entry_SYSCALL_64_fastpath+0x12/0x6d
>>> [  247.834725]
>>> [  247.834726] Leftover inexact backtrace:
>>>
>>> [  247.834728] Code: 24 28 ba d6 01 00 00 48 c7 c6 30 43 62 a0 8b 41 
>>> 2c 89 44 24 08 48 8b 41 20 48 c7 c1 78 a3 62 a0 48 89 04 24 31 c0 e8 
>>> a0 97 f9 ff <0f> 0b 3d 00 fe ff ff 0f 84 ab fd ff ff 83 f8 fc 0f 84 
>>> a2 fd ff
>>> [  247.834748] RIP  [<ffffffffa05c8c30>] 
>>> ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
>>> [  247.834774]  RSP <ffff880074e6bd50>
>>> "
>>>
>>> It's because ocfs2_inode_lock() get us stale LVB in which the i_size 
>>> is not
>>> equal to the disk i_size. We mistakenly trust the LVB because the 
>>> underlaying
>>> fsdlm dlm_lock() doesn't set lkb_sbflags with DLM_SBF_VALNOTVALID 
>>> properly for
>>> us. But, why?
>>>
>>> The current code tries to downconvert lock without DLM_LKF_VALBLK
>>> flag to tell o2cb don't update RSB's LVB if it's a PR->NULL conversion,
>>> even if the lock resource type needs LVB. This is not the right way 
>>> for fsdlm.
>>>
>>> The fsdlm plugin behaves different on DLM_LKF_VALBLK, it depends on
>>> DLM_LKF_VALBLK to decide if we care about the LVB in the LKB. If 
>>> DLM_LKF_VALBLK
>>> is not set, fsdlm will skip recovering RSB's LVB from this lkb and 
>>> set the right
>>> DLM_SBF_VALNOTVALID appropriately when node failure happens.
>>>
>>> The following diagram briefly illustrates how this crash happens:
>>>
>>> RSB1 is inode metadata lock resource with LOCK_TYPE_USES_LVB;
>>>
>>> The 1st round:
>>>
>>>               Node1                                    Node2
>>> RSB1: PR
>>> RSB1(master): NULL->EX
>>> ocfs2_downconvert_lock(PR->NULL, set_lvb==0)
>>>    ocfs2_dlm_lock(no DLM_LKF_VALBLK)
>>>
>>> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>>>
>>> dlm_lock(no DLM_LKF_VALBLK)
>>>    convert_lock(overwrite lkb->lkb_exflags
>>>                 with no DLM_LKF_VALBLK)
>>>
>>> RSB1: NULL                                        RSB1: EX
>>>                                                    reset Node2
>>> dlm_recover_rsbs()
>>>    recover_lvb()
>>>
>>> /* The LVB is not trustable if the node with EX fails and
>>>   * no lock >= PR is left. We should set RSB_VALNOTVALID for RSB1.
>>>   */
>>>
>>>   if(!(kb_exflags & DLM_LKF_VALBLK)) /* This means we miss the 
>>> chance to
>>>             return;                   * to invalid the LVB here.
>>>                                       */
>>>
>>> The 2nd round:
>>>
>>>           Node 1                                Node2
>>> RSB1(become master from recovery)
>>>
>>> ocfs2_setattr()
>>>    ocfs2_inode_lock(NULL->EX)
>>>      /* dlm_lock() return the stale lvb without setting 
>>> DLM_SBF_VALNOTVALID */
>>>      ocfs2_meta_lvb_is_trustable() return 1 /* so we don't refresh 
>>> inode from disk */
>>>    ocfs2_truncate_file()
>>>        mlog_bug_on_msg(disk isize != i_size_read(inode))  /* crash! */
>>>
>>> The fix is quite straightforward. We keep to set DLM_LKF_VALBLK flag 
>>> for dlm_lock()
>>> if the lock resource type needs LVB and the fsdlm plugin is uesed.
>>>
>>> Signed-off-by: Eric Ren <zren@suse.com>
>>> ---
>>>   fs/ocfs2/dlmglue.c   | 10 ++++++++++
>>>   fs/ocfs2/stackglue.c |  6 ++++++
>>>   fs/ocfs2/stackglue.h |  3 +++
>>>   3 files changed, 19 insertions(+)
>>>
>>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>>> index 83d576f..77d1632 100644
>>> --- a/fs/ocfs2/dlmglue.c
>>> +++ b/fs/ocfs2/dlmglue.c
>>> @@ -3303,6 +3303,16 @@ static int ocfs2_downconvert_lock(struct 
>>> ocfs2_super *osb,
>>>       mlog(ML_BASTS, "lockres %s, level %d => %d\n", lockres->l_name,
>>>            lockres->l_level, new_level);
>>>   +    /*
>>> +     * On DLM_LKF_VALBLK, fsdlm behaves differently with o2cb. It 
>>> always
>>> +     * expects DLM_LKF_VALBLK being set if the LKB has LVB, so that
>>> +     * we can recover correctly from node failure. Otherwise, we 
>>> may get
>>> +     * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
>>> +     */
>>> +    if (!ocfs2_is_o2cb_active() &&
>>> +        lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
>>> +        lvb = 1;
>>> +
>>>       if (lvb)
>>>           dlm_flags |= DLM_LKF_VALBLK;
>>>   diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
>>> index 52c07346b..8203590 100644
>>> --- a/fs/ocfs2/stackglue.c
>>> +++ b/fs/ocfs2/stackglue.c
>>> @@ -48,6 +48,12 @@ static char 
>>> ocfs2_hb_ctl_path[OCFS2_MAX_HB_CTL_PATH] = "/sbin/ocfs2_hb_ctl";
>>>    */
>>>   static struct ocfs2_stack_plugin *active_stack;
>>>   +inline int ocfs2_is_o2cb_active(void)
>>> +{
>>> +    return !strcmp(active_stack->sp_name, OCFS2_STACK_PLUGIN_O2CB);
>>> +}
>>> +EXPORT_SYMBOL_GPL(ocfs2_is_o2cb_active);
>>> +
>>>   static struct ocfs2_stack_plugin *ocfs2_stack_lookup(const char 
>>> *name)
>>>   {
>>>       struct ocfs2_stack_plugin *p;
>>> diff --git a/fs/ocfs2/stackglue.h b/fs/ocfs2/stackglue.h
>>> index f2dce10..e3036e1 100644
>>> --- a/fs/ocfs2/stackglue.h
>>> +++ b/fs/ocfs2/stackglue.h
>>> @@ -298,6 +298,9 @@ void 
>>> ocfs2_stack_glue_set_max_proto_version(struct ocfs2_protocol_version 
>>> *max_p
>>>   int ocfs2_stack_glue_register(struct ocfs2_stack_plugin *plugin);
>>>   void ocfs2_stack_glue_unregister(struct ocfs2_stack_plugin *plugin);
>>>   +/* In ocfs2_downconvert_lock(), we need to know which stack we 
>>> are using */
>>> +int ocfs2_is_o2cb_active(void);
>>> +
>>>   extern struct kset *ocfs2_kset;
>>>     #endif  /* STACKGLUE_H */
>>
>>
>
Andrew Morton Dec. 20, 2016, 10:51 p.m. UTC | #6
On Mon, 19 Dec 2016 17:55:06 +0800 Joseph Qi <jiangqi903@gmail.com> wrote:

> > I'd like to see this quick and small fix to be merged at this moment, 
> > because this issue is little emergency for us.
> > Anyway, we can supersede this one easily if someone familiar with o2cb 
> > works out a patch for o2cb in the future.
> >
> > Does this sounds good to you?
> 
> Fine.
> Reviewed-by: Joseph Qi <jiangqi903@gmail.com>

I'll add cc:stable to this one so the fix gets backported into older
kernels.

Patch
diff mbox

diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 83d576f..77d1632 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -3303,6 +3303,16 @@  static int ocfs2_downconvert_lock(struct ocfs2_super *osb,
 	mlog(ML_BASTS, "lockres %s, level %d => %d\n", lockres->l_name,
 	     lockres->l_level, new_level);
 
+	/*
+	 * On DLM_LKF_VALBLK, fsdlm behaves differently with o2cb. It always
+	 * expects DLM_LKF_VALBLK being set if the LKB has LVB, so that
+	 * we can recover correctly from node failure. Otherwise, we may get
+	 * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
+	 */
+	if (!ocfs2_is_o2cb_active() &&
+	    lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
+		lvb = 1;
+
 	if (lvb)
 		dlm_flags |= DLM_LKF_VALBLK;
 
diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
index 52c07346b..8203590 100644
--- a/fs/ocfs2/stackglue.c
+++ b/fs/ocfs2/stackglue.c
@@ -48,6 +48,12 @@  static char ocfs2_hb_ctl_path[OCFS2_MAX_HB_CTL_PATH] = "/sbin/ocfs2_hb_ctl";
  */
 static struct ocfs2_stack_plugin *active_stack;
 
+inline int ocfs2_is_o2cb_active(void)
+{
+	return !strcmp(active_stack->sp_name, OCFS2_STACK_PLUGIN_O2CB);
+}
+EXPORT_SYMBOL_GPL(ocfs2_is_o2cb_active);
+
 static struct ocfs2_stack_plugin *ocfs2_stack_lookup(const char *name)
 {
 	struct ocfs2_stack_plugin *p;
diff --git a/fs/ocfs2/stackglue.h b/fs/ocfs2/stackglue.h
index f2dce10..e3036e1 100644
--- a/fs/ocfs2/stackglue.h
+++ b/fs/ocfs2/stackglue.h
@@ -298,6 +298,9 @@  void ocfs2_stack_glue_set_max_proto_version(struct ocfs2_protocol_version *max_p
 int ocfs2_stack_glue_register(struct ocfs2_stack_plugin *plugin);
 void ocfs2_stack_glue_unregister(struct ocfs2_stack_plugin *plugin);
 
+/* In ocfs2_downconvert_lock(), we need to know which stack we are using */
+int ocfs2_is_o2cb_active(void);
+
 extern struct kset *ocfs2_kset;
 
 #endif  /* STACKGLUE_H */