From: Roman Gushchin <guro@fb.com>
To: Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>
Cc: <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-mm@kvack.org>, Alexander Viro <viro@zeniv.linux.org.uk>,
Jan Kara <jack@suse.cz>, Dennis Zhou <dennis@kernel.org>,
Dave Chinner <dchinner@redhat.com>, <cgroups@vger.kernel.org>,
Roman Gushchin <guro@fb.com>
Subject: [PATCH v9 2/8] writeback, cgroup: add smp_mb() to cgroup_writeback_umount()
Date: Tue, 8 Jun 2021 16:02:19 -0700 [thread overview]
Message-ID: <20210608230225.2078447-3-guro@fb.com> (raw)
In-Reply-To: <20210608230225.2078447-1-guro@fb.com>
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>
Reviewed-by: Jan Kara <jack@suse.cz>
---
fs/fs-writeback.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 7d2891d7ac12..b6fc13a4962d 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
next prev parent reply other threads:[~2021-06-08 23:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 23:02 [PATCH v9 0/8] cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups Roman Gushchin
2021-06-08 23:02 ` [PATCH v9 1/8] writeback, cgroup: do not switch inodes with I_WILL_FREE flag Roman Gushchin
2021-06-08 23:02 ` Roman Gushchin [this message]
2021-06-08 23:02 ` [PATCH v9 4/8] writeback, cgroup: switch to rcu_work API in inode_switch_wbs() Roman Gushchin
2021-06-08 23:02 ` [PATCH v9 5/8] writeback, cgroup: keep list of inodes attached to bdi_writeback Roman Gushchin
2021-06-08 23:02 ` [PATCH v9 6/8] writeback, cgroup: split out the functional part of inode_switch_wbs_work_fn() Roman Gushchin
2021-06-08 23:02 ` [PATCH v9 7/8] writeback, cgroup: support switching multiple inodes at once Roman Gushchin
2021-06-08 23:02 ` [PATCH v9 8/8] writeback, cgroup: release dying cgwbs by switching attached inodes Roman Gushchin
2021-06-09 0:12 ` Andrew Morton
2021-06-09 0:23 ` Roman Gushchin
2021-06-09 0:37 ` Dennis Zhou
2021-06-09 5:34 ` Andrew Morton
2021-06-09 19:53 ` Roman Gushchin
[not found] ` <20210608230225.2078447-4-guro@fb.com>
2021-06-09 3:32 ` [PATCH v9 3/8] writeback, cgroup: increment isw_nr_in_flight before grabbing an inode Ming Lei
2021-06-10 0:21 ` Roman Gushchin
2021-06-10 6:57 ` Ming Lei
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210608230225.2078447-3-guro@fb.com \
--to=guro@fb.com \
--cc=akpm@linux-foundation.org \
--cc=cgroups@vger.kernel.org \
--cc=dchinner@redhat.com \
--cc=dennis@kernel.org \
--cc=jack@suse.cz \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=tj@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).