On Thu 24-09-20 11:00:34, Theodore Y. Ts'o wrote:
> On Fri, Sep 18, 2020 at 11:56:53AM +0200, Jan Kara wrote:
> > 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.
>
> Did you send a v2 of this patch? I can't find it in my inbox...
Yeah, somehow I forgot to send it. I've sent it now:
https://lore.kernel.org/linux-ext4/20200924150959.4335-1-jack@xxxxxxx
Note that Ye Bin's patch will need trivial context fixup after applying
this...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
