diff mbox series

[PATCHv2,1/1] ext4: mballoc: Use this_cpu_read instead of this_cpu_ptr

Message ID 534f275016296996f54ecf65168bb3392b6f653d.1591699601.git.riteshh@linux.ibm.com (mailing list archive)
State New, archived
Headers show
Series [PATCHv2,1/1] ext4: mballoc: Use this_cpu_read instead of this_cpu_ptr | expand

Commit Message

Ritesh Harjani June 9, 2020, 10:53 a.m. UTC
Simplify reading a seq variable by directly using this_cpu_read API
instead of doing this_cpu_ptr and then dereferencing it.

This also avoid the below kernel BUG: which happens when
CONFIG_DEBUG_PREEMPT is enabled

BUG: using smp_processor_id() in preemptible [00000000] code: syz-fuzzer/6927
caller is ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711
CPU: 1 PID: 6927 Comm: syz-fuzzer Not tainted 5.7.0-next-20200602-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 check_preemption_disabled+0x20d/0x220 lib/smp_processor_id.c:48
 ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711
 ext4_ext_map_blocks+0x201b/0x33e0 fs/ext4/extents.c:4244
 ext4_map_blocks+0x4cb/0x1640 fs/ext4/inode.c:626
 ext4_getblk+0xad/0x520 fs/ext4/inode.c:833
 ext4_bread+0x7c/0x380 fs/ext4/inode.c:883
 ext4_append+0x153/0x360 fs/ext4/namei.c:67
 ext4_init_new_dir fs/ext4/namei.c:2757 [inline]
 ext4_mkdir+0x5e0/0xdf0 fs/ext4/namei.c:2802
 vfs_mkdir+0x419/0x690 fs/namei.c:3632
 do_mkdirat+0x21e/0x280 fs/namei.c:3655
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 42f56b7a4a7d ("ext4: mballoc: introduce pcpu seqcnt for freeing PA
to improve ENOSPC handling")
Suggested-by: Borislav Petkov <bp@alien8.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reported-by: syzbot+82f324bb69744c5f6969@syzkaller.appspotmail.com
---
 fs/ext4/mballoc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Christoph Hellwig June 10, 2020, 6:25 a.m. UTC | #1
On Tue, Jun 09, 2020 at 04:23:10PM +0530, Ritesh Harjani wrote:
> Simplify reading a seq variable by directly using this_cpu_read API
> instead of doing this_cpu_ptr and then dereferencing it.
> 
> This also avoid the below kernel BUG: which happens when
> CONFIG_DEBUG_PREEMPT is enabled

I see this warning all the time with ext4 using tests VMs, so lets get
this fixed ASAP before -rc1:

Reviewed-by: Christoph Hellwig <hch@lst.de>
Ritesh Harjani June 10, 2020, 6:34 a.m. UTC | #2
On 6/10/20 11:55 AM, Christoph Hellwig wrote:
> On Tue, Jun 09, 2020 at 04:23:10PM +0530, Ritesh Harjani wrote:
>> Simplify reading a seq variable by directly using this_cpu_read API
>> instead of doing this_cpu_ptr and then dereferencing it.
>>
>> This also avoid the below kernel BUG: which happens when
>> CONFIG_DEBUG_PREEMPT is enabled
> 
> I see this warning all the time with ext4 using tests VMs, so lets get
> this fixed ASAP before -rc1:

Couldn't agree more.

> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> 

Thanks

-ritesh
Theodore Ts'o June 11, 2020, 3:03 p.m. UTC | #3
On Tue, Jun 09, 2020 at 11:25:38PM -0700, Christoph Hellwig wrote:
> On Tue, Jun 09, 2020 at 04:23:10PM +0530, Ritesh Harjani wrote:
> > Simplify reading a seq variable by directly using this_cpu_read API
> > instead of doing this_cpu_ptr and then dereferencing it.
> > 
> > This also avoid the below kernel BUG: which happens when
> > CONFIG_DEBUG_PREEMPT is enabled
> 
> I see this warning all the time with ext4 using tests VMs, so lets get
> this fixed ASAP before -rc1:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks, applied.

						- Ted
diff mbox series

Patch

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a9083113a8c0..c0a331e2feb0 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4708,7 +4708,7 @@  ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
 	}
 
 	ac->ac_op = EXT4_MB_HISTORY_PREALLOC;
-	seq = *this_cpu_ptr(&discard_pa_seq);
+	seq = this_cpu_read(discard_pa_seq);
 	if (!ext4_mb_use_preallocated(ac)) {
 		ac->ac_op = EXT4_MB_HISTORY_ALLOC;
 		ext4_mb_normalize_request(ac, ar);