Re: possible deadlock in fs_reclaim_acquire (2)

On Thu 11-02-21 20:04:14, Hillf Danton wrote:

On Thu 11-02-21 12:07:29, Jan Kara wrote:

quoted

quoted

Fix 71b565ceff37 ("ext4: drop ext4_kvmalloc()") by restoring the
GFP_NOFS introduced in dec214d00e0d ("ext4: xattr inode deduplication").

Note this may be the fix also to possible deadlock
 Reported-by: syzbot+bfdded10ab7dcd7507ae@syzkaller.appspotmail.com
 https://lore.kernel.org/linux-ext4/000000000000563a0205bafb7970@google.com/ (local)

Please no. Ext4 is using scoping API to limit allocations to GFP_NOFS
inside transactions. In this case something didn't work which seems like a
lockdep bug at the first sight but I'll talk to mm guys about it.
Definitely to problem doesn't seem to be in ext4.

Feel free to elaborate why we can find ext4  in the report?
Why is ext4 special in this case?

Please read my reply to the syzbot report [1]. It has all the details.

[1] https://lore.kernel.org/lkml/20210211104947.GL19070@quack2.suse.cz (local)

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR