From: Jan Kara <jack@suse.cz>
To: Ritesh Harjani <riteshh@linux.ibm.com>
Cc: Ye Bin <yebin10@huawei.com>,
adilger.kernel@dilger.ca, jack@suse.com,
linux-ext4@vger.kernel.org, jack@suse.cz, tytso@mit.edu
Subject: Re: [PATCH v5 1/2] ext4: Discard preallocations before releasing group lock
Date: Fri, 18 Sep 2020 11:56:53 +0200 [thread overview]
Message-ID: <20200918095653.GF18920@quack2.suse.cz> (raw)
In-Reply-To: <0f17c3a5-2785-939b-47c5-55d39b4bf67b@linux.ibm.com>
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@suse.cz>
> >
> > 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@suse.cz>
> > Signed-off-by: Ye Bin <yebin10@huawei.com>
> > Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
...
> > + /* 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@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-09-18 9:56 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-16 11:38 [PATCH v5 0/2] Fix dead loop in ext4_mb_new_blocks Ye Bin
2020-09-16 11:38 ` [PATCH v5 1/2] ext4: Discard preallocations before releasing group lock Ye Bin
2020-09-18 9:07 ` Ritesh Harjani
2020-09-18 9:56 ` Jan Kara [this message]
2020-09-24 15:00 ` Theodore Y. Ts'o
2020-09-24 15:12 ` Jan Kara
2020-09-24 14:58 ` Theodore Y. Ts'o
2020-09-16 11:38 ` [PATCH v5 2/2] ext4: Fix dead loop in ext4_mb_new_blocks Ye Bin
2020-09-24 14:59 ` Theodore Y. Ts'o
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