Re: possible deadlock in fs_reclaim_acquire (2)

[Jan Kara]

On Thu 11-02-21 20:04:14, Hillf Danton wrote:
> On Thu 11-02-21 12:07:29, Jan Kara wrote:
> >> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> >>  https://lore.kernel.org/linux-ext4/000000000000563a0205bafb7970@xxxxxxxxxx/
> >
> >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@xxxxxxxxxxxxxx

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR