On Fri 18-09-20 14:37:15, Ritesh Harjani wrote:
>
>
> On 9/16/20 5:08 PM, Ye Bin wrote:
> > From: Jan Kara <jack@xxxxxxx>
> >
> > ext4_mb_discard_group_preallocations() can be releasing group lock with
> > preallocations accumulated on its local list. Thus although
> > discard_pa_seq was incremented and concurrent allocating processes will
> > be retrying allocations, it can happen that premature ENOSPC error is
> > returned because blocks used for preallocations are not available for
> > reuse yet. Make sure we always free locally accumulated preallocations
> > before releasing group lock.
> >
> > Fixes: 07b5b8e1ac40 ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling")
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
> > Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
...
> > + /* if we still need more blocks and some PAs were used, try again */
> > + if (free < needed && busy) {
> > + ext4_unlock_group(sb, group);
> > + cond_resched();
> > + busy = 0;
> > + /* Make sure we increment discard_pa_seq again */
> > + needed -= free;
> > + free = 0;
>
> Oops sorry about getting back to this.
> But if we are making free 0 here so we may return a wrong free value
> when we return from this function. We should fix that by also accounting
> previous freed blocks at the time of final return from this function.
Ah, good catch! I'll send v2 with this fixed up.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
