diff mbox series

[v2] btrfs: fix lockdep warning while mounting sprout fs

Message ID 23a8830f3be500995e74b45f18862e67c0634c3d.1614793362.git.anand.jain@oracle.com (mailing list archive)
State New, archived
Headers show
Series [v2] btrfs: fix lockdep warning while mounting sprout fs | expand

Commit Message

Anand Jain March 3, 2021, 6:10 p.m. UTC
Following test case reproduces lockdep warning.

Test case:
DEV1=/dev/vdb
DEV2=/dev/vdc
umount /btrfs
run mkfs.btrfs -f $DEV1
run btrfstune -S 1 $DEV1
run mount $DEV1 /btrfs
run btrfs device add $DEV2 /btrfs -f
run umount /btrfs
run mount $DEV2 /btrfs
run umount /btrfs

The warning claims a possible ABBA deadlock between the threads initiated by
[#1] btrfs device add and [#0] the mount.

======================================================
[ 540.743122] WARNING: possible circular locking dependency detected
[ 540.743129] 5.11.0-rc7+ #5 Not tainted
[ 540.743135] ------------------------------------------------------
[ 540.743142] mount/2515 is trying to acquire lock:
[ 540.743149] ffffa0c5544c2ce0 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: clone_fs_devices+0x6d/0x210 [btrfs]
[ 540.743458] but task is already holding lock:
[ 540.743461] ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at: __btrfs_tree_read_lock+0x32/0x200 [btrfs]
[ 540.743541] which lock already depends on the new lock.
[ 540.743543] the existing dependency chain (in reverse order) is:

[ 540.743546] -> #1 (btrfs-chunk-00){++++}-{4:4}:
[ 540.743566] down_read_nested+0x48/0x2b0
[ 540.743585] __btrfs_tree_read_lock+0x32/0x200 [btrfs]
[ 540.743650] btrfs_read_lock_root_node+0x70/0x200 [btrfs]
[ 540.743733] btrfs_search_slot+0x6c6/0xe00 [btrfs]
[ 540.743785] btrfs_update_device+0x83/0x260 [btrfs]
[ 540.743849] btrfs_finish_chunk_alloc+0x13f/0x660 [btrfs] <--- device_list_mutex
[ 540.743911] btrfs_create_pending_block_groups+0x18d/0x3f0 [btrfs]
[ 540.743982] btrfs_commit_transaction+0x86/0x1260 [btrfs]
[ 540.744037] btrfs_init_new_device+0x1600/0x1dd0 [btrfs]
[ 540.744101] btrfs_ioctl+0x1c77/0x24c0 [btrfs]
[ 540.744166] __x64_sys_ioctl+0xe4/0x140
[ 540.744170] do_syscall_64+0x4b/0x80
[ 540.744174] entry_SYSCALL_64_after_hwframe+0x44/0xa9

[ 540.744180] -> #0 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
[ 540.744184] __lock_acquire+0x155f/0x2360
[ 540.744188] lock_acquire+0x10b/0x5c0
[ 540.744190] __mutex_lock+0xb1/0xf80
[ 540.744193] mutex_lock_nested+0x27/0x30
[ 540.744196] clone_fs_devices+0x6d/0x210 [btrfs]
[ 540.744270] btrfs_read_chunk_tree+0x3c7/0xbb0 [btrfs]
[ 540.744336] open_ctree+0xf6e/0x2074 [btrfs]
[ 540.744406] btrfs_mount_root.cold.72+0x16/0x127 [btrfs]
[ 540.744472] legacy_get_tree+0x38/0x90
[ 540.744475] vfs_get_tree+0x30/0x140
[ 540.744478] fc_mount+0x16/0x60
[ 540.744482] vfs_kern_mount+0x91/0x100
[ 540.744484] btrfs_mount+0x1e6/0x670 [btrfs]
[ 540.744536] legacy_get_tree+0x38/0x90
[ 540.744537] vfs_get_tree+0x30/0x140
[ 540.744539] path_mount+0x8d8/0x1070
[ 540.744541] do_mount+0x8d/0xc0
[ 540.744543] __x64_sys_mount+0x125/0x160
[ 540.744545] do_syscall_64+0x4b/0x80
[ 540.744547] entry_SYSCALL_64_after_hwframe+0x44/0xa9

[ 540.744551] other info that might help us debug this:
[ 540.744552] Possible unsafe locking scenario:

[ 540.744553] CPU0 				CPU1
[ 540.744554] ---- 				----
[ 540.744555] lock(btrfs-chunk-00);
[ 540.744557] 					lock(&fs_devs->device_list_mutex);
[ 540.744560] 					lock(btrfs-chunk-00);
[ 540.744562] lock(&fs_devs->device_list_mutex);
[ 540.744564]
 *** DEADLOCK ***

[ 540.744565] 3 locks held by mount/2515:
[ 540.744567] #0: ffffa0c56bf7a0e0 (&type->s_umount_key#42/1){+.+.}-{4:4}, at: alloc_super.isra.16+0xdf/0x450
[ 540.744574] #1: ffffffffc05a9628 (uuid_mutex){+.+.}-{4:4}, at: btrfs_read_chunk_tree+0x63/0xbb0 [btrfs]
[ 540.744640] #2: ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at: __btrfs_tree_read_lock+0x32/0x200 [btrfs]
[ 540.744708]
 stack backtrace:
[ 540.744712] CPU: 2 PID: 2515 Comm: mount Not tainted 5.11.0-rc7+ #5


But the device_list_mutex in clone_fs_devices() is redundant, as explained
below.
Two threads [1]  and [2] (below) could lead to clone_fs_device().

[1]
open_ctree <== mount sprout fs
 btrfs_read_chunk_tree()
  mutex_lock(&uuid_mutex) <== global lock
  read_one_dev()
   open_seed_devices()
    clone_fs_devices() <== seed fs_devices
     mutex_lock(&orig->device_list_mutex) <== seed fs_devices

[2]
btrfs_init_new_device() <== sprouting
 mutex_lock(&uuid_mutex); <== global lock
 btrfs_prepare_sprout()
   lockdep_assert_held(&uuid_mutex)
   clone_fs_devices(seed_fs_device) <== seed fs_devices

Both of these threads hold uuid_mutex which is sufficient to protect
getting the seed device(s) freed while we are trying to clone it for
sprouting [2] or mounting a sprout [1] (as above). A mounted seed
device can not free/write/replace because it is read-only. An unmounted
seed device can free by btrfs_free_stale_devices(), but it needs uuid_mutex.
So this patch removes the unnecessary device_list_mutex in clone_fs_devices().
And adds a lockdep_assert_held(&uuid_mutex) in clone_fs_devices().

Reported-by: Su Yue <l@damenly.su>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
v2: Remove Martin's Reported-by and Tested-by.
    Add Su's Reported-by.
    Add lockdep_assert_held check.
    Update the changelog, make it relevant to the current misc-next

 fs/btrfs/volumes.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Comments

Anand Jain March 6, 2021, 8:37 a.m. UTC | #1
David,

  Ping?

Thanks, Anand


On 04/03/2021 02:10, Anand Jain wrote:
> Following test case reproduces lockdep warning.
> 
> Test case:
> DEV1=/dev/vdb
> DEV2=/dev/vdc
> umount /btrfs
> run mkfs.btrfs -f $DEV1
> run btrfstune -S 1 $DEV1
> run mount $DEV1 /btrfs
> run btrfs device add $DEV2 /btrfs -f
> run umount /btrfs
> run mount $DEV2 /btrfs
> run umount /btrfs
> 
> The warning claims a possible ABBA deadlock between the threads initiated by
> [#1] btrfs device add and [#0] the mount.
> 
> ======================================================
> [ 540.743122] WARNING: possible circular locking dependency detected
> [ 540.743129] 5.11.0-rc7+ #5 Not tainted
> [ 540.743135] ------------------------------------------------------
> [ 540.743142] mount/2515 is trying to acquire lock:
> [ 540.743149] ffffa0c5544c2ce0 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: clone_fs_devices+0x6d/0x210 [btrfs]
> [ 540.743458] but task is already holding lock:
> [ 540.743461] ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at: __btrfs_tree_read_lock+0x32/0x200 [btrfs]
> [ 540.743541] which lock already depends on the new lock.
> [ 540.743543] the existing dependency chain (in reverse order) is:
> 
> [ 540.743546] -> #1 (btrfs-chunk-00){++++}-{4:4}:
> [ 540.743566] down_read_nested+0x48/0x2b0
> [ 540.743585] __btrfs_tree_read_lock+0x32/0x200 [btrfs]
> [ 540.743650] btrfs_read_lock_root_node+0x70/0x200 [btrfs]
> [ 540.743733] btrfs_search_slot+0x6c6/0xe00 [btrfs]
> [ 540.743785] btrfs_update_device+0x83/0x260 [btrfs]
> [ 540.743849] btrfs_finish_chunk_alloc+0x13f/0x660 [btrfs] <--- device_list_mutex
> [ 540.743911] btrfs_create_pending_block_groups+0x18d/0x3f0 [btrfs]
> [ 540.743982] btrfs_commit_transaction+0x86/0x1260 [btrfs]
> [ 540.744037] btrfs_init_new_device+0x1600/0x1dd0 [btrfs]
> [ 540.744101] btrfs_ioctl+0x1c77/0x24c0 [btrfs]
> [ 540.744166] __x64_sys_ioctl+0xe4/0x140
> [ 540.744170] do_syscall_64+0x4b/0x80
> [ 540.744174] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> [ 540.744180] -> #0 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
> [ 540.744184] __lock_acquire+0x155f/0x2360
> [ 540.744188] lock_acquire+0x10b/0x5c0
> [ 540.744190] __mutex_lock+0xb1/0xf80
> [ 540.744193] mutex_lock_nested+0x27/0x30
> [ 540.744196] clone_fs_devices+0x6d/0x210 [btrfs]
> [ 540.744270] btrfs_read_chunk_tree+0x3c7/0xbb0 [btrfs]
> [ 540.744336] open_ctree+0xf6e/0x2074 [btrfs]
> [ 540.744406] btrfs_mount_root.cold.72+0x16/0x127 [btrfs]
> [ 540.744472] legacy_get_tree+0x38/0x90
> [ 540.744475] vfs_get_tree+0x30/0x140
> [ 540.744478] fc_mount+0x16/0x60
> [ 540.744482] vfs_kern_mount+0x91/0x100
> [ 540.744484] btrfs_mount+0x1e6/0x670 [btrfs]
> [ 540.744536] legacy_get_tree+0x38/0x90
> [ 540.744537] vfs_get_tree+0x30/0x140
> [ 540.744539] path_mount+0x8d8/0x1070
> [ 540.744541] do_mount+0x8d/0xc0
> [ 540.744543] __x64_sys_mount+0x125/0x160
> [ 540.744545] do_syscall_64+0x4b/0x80
> [ 540.744547] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> [ 540.744551] other info that might help us debug this:
> [ 540.744552] Possible unsafe locking scenario:
> 
> [ 540.744553] CPU0 				CPU1
> [ 540.744554] ---- 				----
> [ 540.744555] lock(btrfs-chunk-00);
> [ 540.744557] 					lock(&fs_devs->device_list_mutex);
> [ 540.744560] 					lock(btrfs-chunk-00);
> [ 540.744562] lock(&fs_devs->device_list_mutex);
> [ 540.744564]
>   *** DEADLOCK ***
> 
> [ 540.744565] 3 locks held by mount/2515:
> [ 540.744567] #0: ffffa0c56bf7a0e0 (&type->s_umount_key#42/1){+.+.}-{4:4}, at: alloc_super.isra.16+0xdf/0x450
> [ 540.744574] #1: ffffffffc05a9628 (uuid_mutex){+.+.}-{4:4}, at: btrfs_read_chunk_tree+0x63/0xbb0 [btrfs]
> [ 540.744640] #2: ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at: __btrfs_tree_read_lock+0x32/0x200 [btrfs]
> [ 540.744708]
>   stack backtrace:
> [ 540.744712] CPU: 2 PID: 2515 Comm: mount Not tainted 5.11.0-rc7+ #5
> 
> 
> But the device_list_mutex in clone_fs_devices() is redundant, as explained
> below.
> Two threads [1]  and [2] (below) could lead to clone_fs_device().
> 
> [1]
> open_ctree <== mount sprout fs
>   btrfs_read_chunk_tree()
>    mutex_lock(&uuid_mutex) <== global lock
>    read_one_dev()
>     open_seed_devices()
>      clone_fs_devices() <== seed fs_devices
>       mutex_lock(&orig->device_list_mutex) <== seed fs_devices
> 
> [2]
> btrfs_init_new_device() <== sprouting
>   mutex_lock(&uuid_mutex); <== global lock
>   btrfs_prepare_sprout()
>     lockdep_assert_held(&uuid_mutex)
>     clone_fs_devices(seed_fs_device) <== seed fs_devices
> 
> Both of these threads hold uuid_mutex which is sufficient to protect
> getting the seed device(s) freed while we are trying to clone it for
> sprouting [2] or mounting a sprout [1] (as above). A mounted seed
> device can not free/write/replace because it is read-only. An unmounted
> seed device can free by btrfs_free_stale_devices(), but it needs uuid_mutex.
> So this patch removes the unnecessary device_list_mutex in clone_fs_devices().
> And adds a lockdep_assert_held(&uuid_mutex) in clone_fs_devices().
> 
> Reported-by: Su Yue <l@damenly.su>
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
> v2: Remove Martin's Reported-by and Tested-by.
>      Add Su's Reported-by.
>      Add lockdep_assert_held check.
>      Update the changelog, make it relevant to the current misc-next
> 
>   fs/btrfs/volumes.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index bc3b33efddc5..4188edbad2ef 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -570,6 +570,8 @@ static int btrfs_free_stale_devices(const char *path,
>   	struct btrfs_device *device, *tmp_device;
>   	int ret = 0;
>   
> +	lockdep_assert_held(&uuid_mutex);
> +
>   	if (path)
>   		ret = -ENOENT;
>   
> @@ -1000,11 +1002,12 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
>   	struct btrfs_device *orig_dev;
>   	int ret = 0;
>   
> +	lockdep_assert_held(&uuid_mutex);
> +
>   	fs_devices = alloc_fs_devices(orig->fsid, NULL);
>   	if (IS_ERR(fs_devices))
>   		return fs_devices;
>   
> -	mutex_lock(&orig->device_list_mutex);
>   	fs_devices->total_devices = orig->total_devices;
>   
>   	list_for_each_entry(orig_dev, &orig->devices, dev_list) {
> @@ -1036,10 +1039,8 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
>   		device->fs_devices = fs_devices;
>   		fs_devices->num_devices++;
>   	}
> -	mutex_unlock(&orig->device_list_mutex);
>   	return fs_devices;
>   error:
> -	mutex_unlock(&orig->device_list_mutex);
>   	free_fs_devices(fs_devices);
>   	return ERR_PTR(ret);
>   }
>
Anand Jain April 5, 2021, 8:38 a.m. UTC | #2
Ping again.

Thanks, Anand

On 06/03/2021 16:37, Anand Jain wrote:
> 
> David,
> 
> Ping?
> 
> Thanks, Anand
> 
> 
> On 04/03/2021 02:10, Anand Jain wrote:
>> Following test case reproduces lockdep warning.
>>
>> Test case:
>> DEV1=/dev/vdb
>> DEV2=/dev/vdc
>> umount /btrfs
>> run mkfs.btrfs -f $DEV1
>> run btrfstune -S 1 $DEV1
>> run mount $DEV1 /btrfs
>> run btrfs device add $DEV2 /btrfs -f
>> run umount /btrfs
>> run mount $DEV2 /btrfs
>> run umount /btrfs
>>
>> The warning claims a possible ABBA deadlock between the threads 
>> initiated by
>> [#1] btrfs device add and [#0] the mount.
>>
>> ======================================================
>> [ 540.743122] WARNING: possible circular locking dependency detected
>> [ 540.743129] 5.11.0-rc7+ #5 Not tainted
>> [ 540.743135] ------------------------------------------------------
>> [ 540.743142] mount/2515 is trying to acquire lock:
>> [ 540.743149] ffffa0c5544c2ce0 
>> (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: 
>> clone_fs_devices+0x6d/0x210 [btrfs]
>> [ 540.743458] but task is already holding lock:
>> [ 540.743461] ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at: 
>> __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>> [ 540.743541] which lock already depends on the new lock.
>> [ 540.743543] the existing dependency chain (in reverse order) is:
>>
>> [ 540.743546] -> #1 (btrfs-chunk-00){++++}-{4:4}:
>> [ 540.743566] down_read_nested+0x48/0x2b0
>> [ 540.743585] __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>> [ 540.743650] btrfs_read_lock_root_node+0x70/0x200 [btrfs]
>> [ 540.743733] btrfs_search_slot+0x6c6/0xe00 [btrfs]
>> [ 540.743785] btrfs_update_device+0x83/0x260 [btrfs]
>> [ 540.743849] btrfs_finish_chunk_alloc+0x13f/0x660 [btrfs] <--- 
>> device_list_mutex
>> [ 540.743911] btrfs_create_pending_block_groups+0x18d/0x3f0 [btrfs]
>> [ 540.743982] btrfs_commit_transaction+0x86/0x1260 [btrfs]
>> [ 540.744037] btrfs_init_new_device+0x1600/0x1dd0 [btrfs]
>> [ 540.744101] btrfs_ioctl+0x1c77/0x24c0 [btrfs]
>> [ 540.744166] __x64_sys_ioctl+0xe4/0x140
>> [ 540.744170] do_syscall_64+0x4b/0x80
>> [ 540.744174] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> [ 540.744180] -> #0 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
>> [ 540.744184] __lock_acquire+0x155f/0x2360
>> [ 540.744188] lock_acquire+0x10b/0x5c0
>> [ 540.744190] __mutex_lock+0xb1/0xf80
>> [ 540.744193] mutex_lock_nested+0x27/0x30
>> [ 540.744196] clone_fs_devices+0x6d/0x210 [btrfs]
>> [ 540.744270] btrfs_read_chunk_tree+0x3c7/0xbb0 [btrfs]
>> [ 540.744336] open_ctree+0xf6e/0x2074 [btrfs]
>> [ 540.744406] btrfs_mount_root.cold.72+0x16/0x127 [btrfs]
>> [ 540.744472] legacy_get_tree+0x38/0x90
>> [ 540.744475] vfs_get_tree+0x30/0x140
>> [ 540.744478] fc_mount+0x16/0x60
>> [ 540.744482] vfs_kern_mount+0x91/0x100
>> [ 540.744484] btrfs_mount+0x1e6/0x670 [btrfs]
>> [ 540.744536] legacy_get_tree+0x38/0x90
>> [ 540.744537] vfs_get_tree+0x30/0x140
>> [ 540.744539] path_mount+0x8d8/0x1070
>> [ 540.744541] do_mount+0x8d/0xc0
>> [ 540.744543] __x64_sys_mount+0x125/0x160
>> [ 540.744545] do_syscall_64+0x4b/0x80
>> [ 540.744547] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> [ 540.744551] other info that might help us debug this:
>> [ 540.744552] Possible unsafe locking scenario:
>>
>> [ 540.744553] CPU0                 CPU1
>> [ 540.744554] ----                 ----
>> [ 540.744555] lock(btrfs-chunk-00);
>> [ 540.744557]                     lock(&fs_devs->device_list_mutex);
>> [ 540.744560]                     lock(btrfs-chunk-00);
>> [ 540.744562] lock(&fs_devs->device_list_mutex);
>> [ 540.744564]
>>   *** DEADLOCK ***
>>
>> [ 540.744565] 3 locks held by mount/2515:
>> [ 540.744567] #0: ffffa0c56bf7a0e0 
>> (&type->s_umount_key#42/1){+.+.}-{4:4}, at: 
>> alloc_super.isra.16+0xdf/0x450
>> [ 540.744574] #1: ffffffffc05a9628 (uuid_mutex){+.+.}-{4:4}, at: 
>> btrfs_read_chunk_tree+0x63/0xbb0 [btrfs]
>> [ 540.744640] #2: ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at: 
>> __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>> [ 540.744708]
>>   stack backtrace:
>> [ 540.744712] CPU: 2 PID: 2515 Comm: mount Not tainted 5.11.0-rc7+ #5
>>
>>
>> But the device_list_mutex in clone_fs_devices() is redundant, as 
>> explained
>> below.
>> Two threads [1]  and [2] (below) could lead to clone_fs_device().
>>
>> [1]
>> open_ctree <== mount sprout fs
>>   btrfs_read_chunk_tree()
>>    mutex_lock(&uuid_mutex) <== global lock
>>    read_one_dev()
>>     open_seed_devices()
>>      clone_fs_devices() <== seed fs_devices
>>       mutex_lock(&orig->device_list_mutex) <== seed fs_devices
>>
>> [2]
>> btrfs_init_new_device() <== sprouting
>>   mutex_lock(&uuid_mutex); <== global lock
>>   btrfs_prepare_sprout()
>>     lockdep_assert_held(&uuid_mutex)
>>     clone_fs_devices(seed_fs_device) <== seed fs_devices
>>
>> Both of these threads hold uuid_mutex which is sufficient to protect
>> getting the seed device(s) freed while we are trying to clone it for
>> sprouting [2] or mounting a sprout [1] (as above). A mounted seed
>> device can not free/write/replace because it is read-only. An unmounted
>> seed device can free by btrfs_free_stale_devices(), but it needs 
>> uuid_mutex.
>> So this patch removes the unnecessary device_list_mutex in 
>> clone_fs_devices().
>> And adds a lockdep_assert_held(&uuid_mutex) in clone_fs_devices().
>>
>> Reported-by: Su Yue <l@damenly.su>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>> v2: Remove Martin's Reported-by and Tested-by.
>>      Add Su's Reported-by.
>>      Add lockdep_assert_held check.
>>      Update the changelog, make it relevant to the current misc-next
>>
>>   fs/btrfs/volumes.c | 7 ++++---
>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index bc3b33efddc5..4188edbad2ef 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -570,6 +570,8 @@ static int btrfs_free_stale_devices(const char *path,
>>       struct btrfs_device *device, *tmp_device;
>>       int ret = 0;
>> +    lockdep_assert_held(&uuid_mutex);
>> +
>>       if (path)
>>           ret = -ENOENT;
>> @@ -1000,11 +1002,12 @@ static struct btrfs_fs_devices 
>> *clone_fs_devices(struct btrfs_fs_devices *orig)
>>       struct btrfs_device *orig_dev;
>>       int ret = 0;
>> +    lockdep_assert_held(&uuid_mutex);
>> +
>>       fs_devices = alloc_fs_devices(orig->fsid, NULL);
>>       if (IS_ERR(fs_devices))
>>           return fs_devices;
>> -    mutex_lock(&orig->device_list_mutex);
>>       fs_devices->total_devices = orig->total_devices;
>>       list_for_each_entry(orig_dev, &orig->devices, dev_list) {
>> @@ -1036,10 +1039,8 @@ static struct btrfs_fs_devices 
>> *clone_fs_devices(struct btrfs_fs_devices *orig)
>>           device->fs_devices = fs_devices;
>>           fs_devices->num_devices++;
>>       }
>> -    mutex_unlock(&orig->device_list_mutex);
>>       return fs_devices;
>>   error:
>> -    mutex_unlock(&orig->device_list_mutex);
>>       free_fs_devices(fs_devices);
>>       return ERR_PTR(ret);
>>   }
>>
>
Su Yue April 5, 2021, 9:18 a.m. UTC | #3
On Mon 05 Apr 2021 at 16:38, Anand Jain <anand.jain@oracle.com> 
wrote:

> Ping again.
>
It's already queued in misc-next.

commit 441737bb30f83914bb8517f52088c0130138d74b (misc-next)
Author: Anand Jain <anand.jain@oracle.com>
Date:   Fri Jul 17 18:05:25 2020 +0800

    btrfs: fix lockdep warning while mounting sprout fs

    Martin reported the following test case which reproduces 
    lockdep

--
Su
> Thanks, Anand
>
> On 06/03/2021 16:37, Anand Jain wrote:
>>
>> David,
>>
>> Ping?
>>
>> Thanks, Anand
>>
>>
>> On 04/03/2021 02:10, Anand Jain wrote:
>>> Following test case reproduces lockdep warning.
>>>
>>> Test case:
>>> DEV1=/dev/vdb
>>> DEV2=/dev/vdc
>>> umount /btrfs
>>> run mkfs.btrfs -f $DEV1
>>> run btrfstune -S 1 $DEV1
>>> run mount $DEV1 /btrfs
>>> run btrfs device add $DEV2 /btrfs -f
>>> run umount /btrfs
>>> run mount $DEV2 /btrfs
>>> run umount /btrfs
>>>
>>> The warning claims a possible ABBA deadlock between the 
>>> threads
>>> initiated by
>>> [#1] btrfs device add and [#0] the mount.
>>>
>>> ======================================================
>>> [ 540.743122] WARNING: possible circular locking dependency 
>>> detected
>>> [ 540.743129] 5.11.0-rc7+ #5 Not tainted
>>> [ 540.743135] 
>>> ------------------------------------------------------
>>> [ 540.743142] mount/2515 is trying to acquire lock:
>>> [ 540.743149] ffffa0c5544c2ce0
>>> (&fs_devs->device_list_mutex){+.+.}-{4:4}, at:
>>> clone_fs_devices+0x6d/0x210 [btrfs]
>>> [ 540.743458] but task is already holding lock:
>>> [ 540.743461] ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, 
>>> at:
>>> __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>>> [ 540.743541] which lock already depends on the new lock.
>>> [ 540.743543] the existing dependency chain (in reverse order) 
>>> is:
>>>
>>> [ 540.743546] -> #1 (btrfs-chunk-00){++++}-{4:4}:
>>> [ 540.743566] down_read_nested+0x48/0x2b0
>>> [ 540.743585] __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>>> [ 540.743650] btrfs_read_lock_root_node+0x70/0x200 [btrfs]
>>> [ 540.743733] btrfs_search_slot+0x6c6/0xe00 [btrfs]
>>> [ 540.743785] btrfs_update_device+0x83/0x260 [btrfs]
>>> [ 540.743849] btrfs_finish_chunk_alloc+0x13f/0x660 [btrfs] 
>>> <---
>>> device_list_mutex
>>> [ 540.743911] btrfs_create_pending_block_groups+0x18d/0x3f0 
>>> [btrfs]
>>> [ 540.743982] btrfs_commit_transaction+0x86/0x1260 [btrfs]
>>> [ 540.744037] btrfs_init_new_device+0x1600/0x1dd0 [btrfs]
>>> [ 540.744101] btrfs_ioctl+0x1c77/0x24c0 [btrfs]
>>> [ 540.744166] __x64_sys_ioctl+0xe4/0x140
>>> [ 540.744170] do_syscall_64+0x4b/0x80
>>> [ 540.744174] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>
>>> [ 540.744180] -> #0 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
>>> [ 540.744184] __lock_acquire+0x155f/0x2360
>>> [ 540.744188] lock_acquire+0x10b/0x5c0
>>> [ 540.744190] __mutex_lock+0xb1/0xf80
>>> [ 540.744193] mutex_lock_nested+0x27/0x30
>>> [ 540.744196] clone_fs_devices+0x6d/0x210 [btrfs]
>>> [ 540.744270] btrfs_read_chunk_tree+0x3c7/0xbb0 [btrfs]
>>> [ 540.744336] open_ctree+0xf6e/0x2074 [btrfs]
>>> [ 540.744406] btrfs_mount_root.cold.72+0x16/0x127 [btrfs]
>>> [ 540.744472] legacy_get_tree+0x38/0x90
>>> [ 540.744475] vfs_get_tree+0x30/0x140
>>> [ 540.744478] fc_mount+0x16/0x60
>>> [ 540.744482] vfs_kern_mount+0x91/0x100
>>> [ 540.744484] btrfs_mount+0x1e6/0x670 [btrfs]
>>> [ 540.744536] legacy_get_tree+0x38/0x90
>>> [ 540.744537] vfs_get_tree+0x30/0x140
>>> [ 540.744539] path_mount+0x8d8/0x1070
>>> [ 540.744541] do_mount+0x8d/0xc0
>>> [ 540.744543] __x64_sys_mount+0x125/0x160
>>> [ 540.744545] do_syscall_64+0x4b/0x80
>>> [ 540.744547] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>
>>> [ 540.744551] other info that might help us debug this:
>>> [ 540.744552] Possible unsafe locking scenario:
>>>
>>> [ 540.744553] CPU0                 CPU1
>>> [ 540.744554] ----                 ----
>>> [ 540.744555] lock(btrfs-chunk-00);
>>> [ 540.744557] 
>>> lock(&fs_devs->device_list_mutex);
>>> [ 540.744560]                     lock(btrfs-chunk-00);
>>> [ 540.744562] lock(&fs_devs->device_list_mutex);
>>> [ 540.744564]
>>>   *** DEADLOCK ***
>>>
>>> [ 540.744565] 3 locks held by mount/2515:
>>> [ 540.744567] #0: ffffa0c56bf7a0e0
>>> (&type->s_umount_key#42/1){+.+.}-{4:4}, at:
>>> alloc_super.isra.16+0xdf/0x450
>>> [ 540.744574] #1: ffffffffc05a9628 (uuid_mutex){+.+.}-{4:4}, 
>>> at:
>>> btrfs_read_chunk_tree+0x63/0xbb0 [btrfs]
>>> [ 540.744640] #2: ffffa0c54a7932b8 
>>> (btrfs-chunk-00){++++}-{4:4}, at:
>>> __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>>> [ 540.744708]
>>>   stack backtrace:
>>> [ 540.744712] CPU: 2 PID: 2515 Comm: mount Not tainted 
>>> 5.11.0-rc7+ #5
>>>
>>>
>>> But the device_list_mutex in clone_fs_devices() is redundant, 
>>> as
>>> explained
>>> below.
>>> Two threads [1]  and [2] (below) could lead to 
>>> clone_fs_device().
>>>
>>> [1]
>>> open_ctree <== mount sprout fs
>>>   btrfs_read_chunk_tree()
>>>    mutex_lock(&uuid_mutex) <== global lock
>>>    read_one_dev()
>>>     open_seed_devices()
>>>      clone_fs_devices() <== seed fs_devices
>>>       mutex_lock(&orig->device_list_mutex) <== seed fs_devices
>>>
>>> [2]
>>> btrfs_init_new_device() <== sprouting
>>>   mutex_lock(&uuid_mutex); <== global lock
>>>   btrfs_prepare_sprout()
>>>     lockdep_assert_held(&uuid_mutex)
>>>     clone_fs_devices(seed_fs_device) <== seed fs_devices
>>>
>>> Both of these threads hold uuid_mutex which is sufficient to 
>>> protect
>>> getting the seed device(s) freed while we are trying to clone 
>>> it for
>>> sprouting [2] or mounting a sprout [1] (as above). A mounted 
>>> seed
>>> device can not free/write/replace because it is read-only. An 
>>> unmounted
>>> seed device can free by btrfs_free_stale_devices(), but it 
>>> needs
>>> uuid_mutex.
>>> So this patch removes the unnecessary device_list_mutex in
>>> clone_fs_devices().
>>> And adds a lockdep_assert_held(&uuid_mutex) in 
>>> clone_fs_devices().
>>>
>>> Reported-by: Su Yue <l@damenly.su>
>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>> ---
>>> v2: Remove Martin's Reported-by and Tested-by.
>>>      Add Su's Reported-by.
>>>      Add lockdep_assert_held check.
>>>      Update the changelog, make it relevant to the current 
>>>      misc-next
>>>
>>>   fs/btrfs/volumes.c | 7 ++++---
>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>>> index bc3b33efddc5..4188edbad2ef 100644
>>> --- a/fs/btrfs/volumes.c
>>> +++ b/fs/btrfs/volumes.c
>>> @@ -570,6 +570,8 @@ static int btrfs_free_stale_devices(const 
>>> char *path,
>>>       struct btrfs_device *device, *tmp_device;
>>>       int ret = 0;
>>> +    lockdep_assert_held(&uuid_mutex);
>>> +
>>>       if (path)
>>>           ret = -ENOENT;
>>> @@ -1000,11 +1002,12 @@ static struct btrfs_fs_devices
>>> *clone_fs_devices(struct btrfs_fs_devices *orig)
>>>       struct btrfs_device *orig_dev;
>>>       int ret = 0;
>>> +    lockdep_assert_held(&uuid_mutex);
>>> +
>>>       fs_devices = alloc_fs_devices(orig->fsid, NULL);
>>>       if (IS_ERR(fs_devices))
>>>           return fs_devices;
>>> -    mutex_lock(&orig->device_list_mutex);
>>>       fs_devices->total_devices = orig->total_devices;
>>>       list_for_each_entry(orig_dev, &orig->devices, dev_list) 
>>>       {
>>> @@ -1036,10 +1039,8 @@ static struct btrfs_fs_devices
>>> *clone_fs_devices(struct btrfs_fs_devices *orig)
>>>           device->fs_devices = fs_devices;
>>>           fs_devices->num_devices++;
>>>       }
>>> -    mutex_unlock(&orig->device_list_mutex);
>>>       return fs_devices;
>>>   error:
>>> -    mutex_unlock(&orig->device_list_mutex);
>>>       free_fs_devices(fs_devices);
>>>       return ERR_PTR(ret);
>>>   }
>>>
>>
Anand Jain April 5, 2021, 9:30 a.m. UTC | #4
On 05/04/2021 17:18, Su Yue wrote:
> 
> On Mon 05 Apr 2021 at 16:38, Anand Jain <anand.jain@oracle.com> wrote:
> 
>> Ping again.
>>
> It's already queued in misc-next.
> 

Oh thanks.

Thanks David.

-Anand


> commit 441737bb30f83914bb8517f52088c0130138d74b (misc-next)
> Author: Anand Jain <anand.jain@oracle.com>
> Date:   Fri Jul 17 18:05:25 2020 +0800
> 
>    btrfs: fix lockdep warning while mounting sprout fs
> 
>    Martin reported the following test case which reproduces   lockdep
> 
> -- 
> Su
>> Thanks, Anand
>>
>> On 06/03/2021 16:37, Anand Jain wrote:
>>>
>>> David,
>>>
>>> Ping?
>>>
>>> Thanks, Anand
>>>
>>>
>>> On 04/03/2021 02:10, Anand Jain wrote:
>>>> Following test case reproduces lockdep warning.
>>>>
>>>> Test case:
>>>> DEV1=/dev/vdb
>>>> DEV2=/dev/vdc
>>>> umount /btrfs
>>>> run mkfs.btrfs -f $DEV1
>>>> run btrfstune -S 1 $DEV1
>>>> run mount $DEV1 /btrfs
>>>> run btrfs device add $DEV2 /btrfs -f
>>>> run umount /btrfs
>>>> run mount $DEV2 /btrfs
>>>> run umount /btrfs
>>>>
>>>> The warning claims a possible ABBA deadlock between the threads
>>>> initiated by
>>>> [#1] btrfs device add and [#0] the mount.
>>>>
>>>> ======================================================
>>>> [ 540.743122] WARNING: possible circular locking dependency detected
>>>> [ 540.743129] 5.11.0-rc7+ #5 Not tainted
>>>> [ 540.743135] ------------------------------------------------------
>>>> [ 540.743142] mount/2515 is trying to acquire lock:
>>>> [ 540.743149] ffffa0c5544c2ce0
>>>> (&fs_devs->device_list_mutex){+.+.}-{4:4}, at:
>>>> clone_fs_devices+0x6d/0x210 [btrfs]
>>>> [ 540.743458] but task is already holding lock:
>>>> [ 540.743461] ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at:
>>>> __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>>>> [ 540.743541] which lock already depends on the new lock.
>>>> [ 540.743543] the existing dependency chain (in reverse order) is:
>>>>
>>>> [ 540.743546] -> #1 (btrfs-chunk-00){++++}-{4:4}:
>>>> [ 540.743566] down_read_nested+0x48/0x2b0
>>>> [ 540.743585] __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>>>> [ 540.743650] btrfs_read_lock_root_node+0x70/0x200 [btrfs]
>>>> [ 540.743733] btrfs_search_slot+0x6c6/0xe00 [btrfs]
>>>> [ 540.743785] btrfs_update_device+0x83/0x260 [btrfs]
>>>> [ 540.743849] btrfs_finish_chunk_alloc+0x13f/0x660 [btrfs] <---
>>>> device_list_mutex
>>>> [ 540.743911] btrfs_create_pending_block_groups+0x18d/0x3f0 [btrfs]
>>>> [ 540.743982] btrfs_commit_transaction+0x86/0x1260 [btrfs]
>>>> [ 540.744037] btrfs_init_new_device+0x1600/0x1dd0 [btrfs]
>>>> [ 540.744101] btrfs_ioctl+0x1c77/0x24c0 [btrfs]
>>>> [ 540.744166] __x64_sys_ioctl+0xe4/0x140
>>>> [ 540.744170] do_syscall_64+0x4b/0x80
>>>> [ 540.744174] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>>
>>>> [ 540.744180] -> #0 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
>>>> [ 540.744184] __lock_acquire+0x155f/0x2360
>>>> [ 540.744188] lock_acquire+0x10b/0x5c0
>>>> [ 540.744190] __mutex_lock+0xb1/0xf80
>>>> [ 540.744193] mutex_lock_nested+0x27/0x30
>>>> [ 540.744196] clone_fs_devices+0x6d/0x210 [btrfs]
>>>> [ 540.744270] btrfs_read_chunk_tree+0x3c7/0xbb0 [btrfs]
>>>> [ 540.744336] open_ctree+0xf6e/0x2074 [btrfs]
>>>> [ 540.744406] btrfs_mount_root.cold.72+0x16/0x127 [btrfs]
>>>> [ 540.744472] legacy_get_tree+0x38/0x90
>>>> [ 540.744475] vfs_get_tree+0x30/0x140
>>>> [ 540.744478] fc_mount+0x16/0x60
>>>> [ 540.744482] vfs_kern_mount+0x91/0x100
>>>> [ 540.744484] btrfs_mount+0x1e6/0x670 [btrfs]
>>>> [ 540.744536] legacy_get_tree+0x38/0x90
>>>> [ 540.744537] vfs_get_tree+0x30/0x140
>>>> [ 540.744539] path_mount+0x8d8/0x1070
>>>> [ 540.744541] do_mount+0x8d/0xc0
>>>> [ 540.744543] __x64_sys_mount+0x125/0x160
>>>> [ 540.744545] do_syscall_64+0x4b/0x80
>>>> [ 540.744547] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>>
>>>> [ 540.744551] other info that might help us debug this:
>>>> [ 540.744552] Possible unsafe locking scenario:
>>>>
>>>> [ 540.744553] CPU0                 CPU1
>>>> [ 540.744554] ----                 ----
>>>> [ 540.744555] lock(btrfs-chunk-00);
>>>> [ 540.744557] lock(&fs_devs->device_list_mutex);
>>>> [ 540.744560]                     lock(btrfs-chunk-00);
>>>> [ 540.744562] lock(&fs_devs->device_list_mutex);
>>>> [ 540.744564]
>>>>   *** DEADLOCK ***
>>>>
>>>> [ 540.744565] 3 locks held by mount/2515:
>>>> [ 540.744567] #0: ffffa0c56bf7a0e0
>>>> (&type->s_umount_key#42/1){+.+.}-{4:4}, at:
>>>> alloc_super.isra.16+0xdf/0x450
>>>> [ 540.744574] #1: ffffffffc05a9628 (uuid_mutex){+.+.}-{4:4}, at:
>>>> btrfs_read_chunk_tree+0x63/0xbb0 [btrfs]
>>>> [ 540.744640] #2: ffffa0c54a7932b8 (btrfs-chunk-00){++++}-{4:4}, at:
>>>> __btrfs_tree_read_lock+0x32/0x200 [btrfs]
>>>> [ 540.744708]
>>>>   stack backtrace:
>>>> [ 540.744712] CPU: 2 PID: 2515 Comm: mount Not tainted 5.11.0-rc7+ #5
>>>>
>>>>
>>>> But the device_list_mutex in clone_fs_devices() is redundant, as
>>>> explained
>>>> below.
>>>> Two threads [1]  and [2] (below) could lead to clone_fs_device().
>>>>
>>>> [1]
>>>> open_ctree <== mount sprout fs
>>>>   btrfs_read_chunk_tree()
>>>>    mutex_lock(&uuid_mutex) <== global lock
>>>>    read_one_dev()
>>>>     open_seed_devices()
>>>>      clone_fs_devices() <== seed fs_devices
>>>>       mutex_lock(&orig->device_list_mutex) <== seed fs_devices
>>>>
>>>> [2]
>>>> btrfs_init_new_device() <== sprouting
>>>>   mutex_lock(&uuid_mutex); <== global lock
>>>>   btrfs_prepare_sprout()
>>>>     lockdep_assert_held(&uuid_mutex)
>>>>     clone_fs_devices(seed_fs_device) <== seed fs_devices
>>>>
>>>> Both of these threads hold uuid_mutex which is sufficient to protect
>>>> getting the seed device(s) freed while we are trying to clone it for
>>>> sprouting [2] or mounting a sprout [1] (as above). A mounted seed
>>>> device can not free/write/replace because it is read-only. An unmounted
>>>> seed device can free by btrfs_free_stale_devices(), but it needs
>>>> uuid_mutex.
>>>> So this patch removes the unnecessary device_list_mutex in
>>>> clone_fs_devices().
>>>> And adds a lockdep_assert_held(&uuid_mutex) in clone_fs_devices().
>>>>
>>>> Reported-by: Su Yue <l@damenly.su>
>>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>>> ---
>>>> v2: Remove Martin's Reported-by and Tested-by.
>>>>      Add Su's Reported-by.
>>>>      Add lockdep_assert_held check.
>>>>      Update the changelog, make it relevant to the current      
>>>> misc-next
>>>>
>>>>   fs/btrfs/volumes.c | 7 ++++---
>>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>>>> index bc3b33efddc5..4188edbad2ef 100644
>>>> --- a/fs/btrfs/volumes.c
>>>> +++ b/fs/btrfs/volumes.c
>>>> @@ -570,6 +570,8 @@ static int btrfs_free_stale_devices(const char 
>>>> *path,
>>>>       struct btrfs_device *device, *tmp_device;
>>>>       int ret = 0;
>>>> +    lockdep_assert_held(&uuid_mutex);
>>>> +
>>>>       if (path)
>>>>           ret = -ENOENT;
>>>> @@ -1000,11 +1002,12 @@ static struct btrfs_fs_devices
>>>> *clone_fs_devices(struct btrfs_fs_devices *orig)
>>>>       struct btrfs_device *orig_dev;
>>>>       int ret = 0;
>>>> +    lockdep_assert_held(&uuid_mutex);
>>>> +
>>>>       fs_devices = alloc_fs_devices(orig->fsid, NULL);
>>>>       if (IS_ERR(fs_devices))
>>>>           return fs_devices;
>>>> -    mutex_lock(&orig->device_list_mutex);
>>>>       fs_devices->total_devices = orig->total_devices;
>>>>       list_for_each_entry(orig_dev, &orig->devices, dev_list)       {
>>>> @@ -1036,10 +1039,8 @@ static struct btrfs_fs_devices
>>>> *clone_fs_devices(struct btrfs_fs_devices *orig)
>>>>           device->fs_devices = fs_devices;
>>>>           fs_devices->num_devices++;
>>>>       }
>>>> -    mutex_unlock(&orig->device_list_mutex);
>>>>       return fs_devices;
>>>>   error:
>>>> -    mutex_unlock(&orig->device_list_mutex);
>>>>       free_fs_devices(fs_devices);
>>>>       return ERR_PTR(ret);
>>>>   }
>>>>
>>>
>
David Sterba April 6, 2021, 4:48 p.m. UTC | #5
On Mon, Apr 05, 2021 at 05:18:32PM +0800, Su Yue wrote:
> 
> On Mon 05 Apr 2021 at 16:38, Anand Jain <anand.jain@oracle.com> 
> wrote:
> 
> > Ping again.
> >
> It's already queued in misc-next.

> commit 441737bb30f83914bb8517f52088c0130138d74b (misc-next)
> Author: Anand Jain <anand.jain@oracle.com>
> Date:   Fri Jul 17 18:05:25 2020 +0800

No it's not, you must have checked some very old snapshot of misc-next,
I don't even have 441737bb30f83914bb8517f52088c0130138d74b in my stale
commit objects so it's been 'git gc'ed already.
Anand Jain April 6, 2021, 11:01 p.m. UTC | #6
On 07/04/2021 00:48, David Sterba wrote:
> On Mon, Apr 05, 2021 at 05:18:32PM +0800, Su Yue wrote:
>>
>> On Mon 05 Apr 2021 at 16:38, Anand Jain <anand.jain@oracle.com>
>> wrote:
>>
>>> Ping again.
>>>
>> It's already queued in misc-next.
> 
>> commit 441737bb30f83914bb8517f52088c0130138d74b (misc-next)
>> Author: Anand Jain <anand.jain@oracle.com>
>> Date:   Fri Jul 17 18:05:25 2020 +0800
> 
> No it's not, you must have checked some very old snapshot of misc-next,
> I don't even have 441737bb30f83914bb8517f52088c0130138d74b in my stale
> commit objects so it's been 'git gc'ed already.

What is holding this patch from the integration?

Thanks, Anand
Su Yue April 7, 2021, 8:24 a.m. UTC | #7
On Wed, Apr 7, 2021 at 3:24 PM David Sterba <dsterba@suse.cz> wrote:
>
> On Mon, Apr 05, 2021 at 05:18:32PM +0800, Su Yue wrote:
> >
> > On Mon 05 Apr 2021 at 16:38, Anand Jain <anand.jain@oracle.com>
> > wrote:
> >
> > > Ping again.
> > >
> > It's already queued in misc-next.
>
> > commit 441737bb30f83914bb8517f52088c0130138d74b (misc-next)
> > Author: Anand Jain <anand.jain@oracle.com>
> > Date:   Fri Jul 17 18:05:25 2020 +0800
>
> No it's not, you must have checked some very old snapshot of misc-next,
> I don't even have 441737bb30f83914bb8517f52088c0130138d74b in my stale
> commit objects so it's been 'git gc'ed already.
Indeed. Sorry for the wrong info.

--
Su
diff mbox series

Patch

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index bc3b33efddc5..4188edbad2ef 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -570,6 +570,8 @@  static int btrfs_free_stale_devices(const char *path,
 	struct btrfs_device *device, *tmp_device;
 	int ret = 0;
 
+	lockdep_assert_held(&uuid_mutex);
+
 	if (path)
 		ret = -ENOENT;
 
@@ -1000,11 +1002,12 @@  static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
 	struct btrfs_device *orig_dev;
 	int ret = 0;
 
+	lockdep_assert_held(&uuid_mutex);
+
 	fs_devices = alloc_fs_devices(orig->fsid, NULL);
 	if (IS_ERR(fs_devices))
 		return fs_devices;
 
-	mutex_lock(&orig->device_list_mutex);
 	fs_devices->total_devices = orig->total_devices;
 
 	list_for_each_entry(orig_dev, &orig->devices, dev_list) {
@@ -1036,10 +1039,8 @@  static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
 		device->fs_devices = fs_devices;
 		fs_devices->num_devices++;
 	}
-	mutex_unlock(&orig->device_list_mutex);
 	return fs_devices;
 error:
-	mutex_unlock(&orig->device_list_mutex);
 	free_fs_devices(fs_devices);
 	return ERR_PTR(ret);
 }