From: Jan Kara <jack@suse.cz>
To: Roman Gushchin <guro@fb.com>
Cc: Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Alexander Viro <viro@zeniv.linux.org.uk>,
Dennis Zhou <dennis@kernel.org>,
Dave Chinner <dchinner@redhat.com>,
cgroups@vger.kernel.org
Subject: Re: [PATCH v8 2/8] writeback, cgroup: add smp_mb() to cgroup_writeback_umount()
Date: Tue, 8 Jun 2021 10:43:48 +0200 [thread overview]
Message-ID: <20210608084348.GA5562@quack2.suse.cz> (raw)
In-Reply-To: <20210608013123.1088882-3-guro@fb.com>
On Mon 07-06-21 18:31:17, Roman Gushchin wrote:
> A full memory barrier is required between clearing SB_ACTIVE flag
> in generic_shutdown_super() and checking isw_nr_in_flight in
> cgroup_writeback_umount(), otherwise a new switch operation might
> be scheduled after atomic_read(&isw_nr_in_flight) returned 0.
> This would result in a non-flushed isw_wq, and a potential crash.
>
> The problem hasn't yet been seen in the real life and was discovered
> by Jan Kara by looking into the code.
>
> Suggested-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Roman Gushchin <guro@fb.com>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/fs-writeback.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index bd99890599e0..3564efcc4b78 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1000,6 +1000,12 @@ int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
> */
> void cgroup_writeback_umount(void)
> {
> + /*
> + * SB_ACTIVE should be reliably cleared before checking
> + * isw_nr_in_flight, see generic_shutdown_super().
> + */
> + smp_mb();
> +
> if (atomic_read(&isw_nr_in_flight)) {
> /*
> * Use rcu_barrier() to wait for all pending callbacks to
> --
> 2.31.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2021-06-08 8:43 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 1:31 [PATCH v8 0/8] cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups Roman Gushchin
2021-06-08 1:31 ` [PATCH v8 1/8] writeback, cgroup: do not switch inodes with I_WILL_FREE flag Roman Gushchin
2021-06-08 1:31 ` [PATCH v8 2/8] writeback, cgroup: add smp_mb() to cgroup_writeback_umount() Roman Gushchin
2021-06-08 8:43 ` Jan Kara [this message]
2021-06-08 1:31 ` [PATCH v8 3/8] writeback, cgroup: increment isw_nr_in_flight before grabbing an inode Roman Gushchin
2021-06-08 8:45 ` Jan Kara
2021-06-08 1:31 ` [PATCH v8 4/8] writeback, cgroup: switch to rcu_work API in inode_switch_wbs() Roman Gushchin
2021-06-08 1:31 ` [PATCH v8 5/8] writeback, cgroup: keep list of inodes attached to bdi_writeback Roman Gushchin
2021-06-08 1:31 ` [PATCH v8 6/8] writeback, cgroup: split out the functional part of inode_switch_wbs_work_fn() Roman Gushchin
2021-06-08 1:31 ` [PATCH v8 7/8] writeback, cgroup: support switching multiple inodes at once Roman Gushchin
2021-06-08 1:31 ` [PATCH v8 8/8] writeback, cgroup: release dying cgwbs by switching attached inodes Roman Gushchin
2021-06-08 8:54 ` Jan Kara
2021-06-08 16:08 ` Dennis Zhou
2021-06-08 22:37 ` Roman Gushchin
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