[merged] writeback-cgroup-add-smp_mb-to-cgroup_writeback_umount.patch removed from -mm tree

[merged] writeback-cgroup-add-smp_mb-to-cgroup_writeback_umount.patch removed from -mm tree

[akpm]

The patch titled
     Subject: writeback, cgroup: add smp_mb() to cgroup_writeback_umount()
has been removed from the -mm tree.  Its filename was
     writeback-cgroup-add-smp_mb-to-cgroup_writeback_umount.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Roman Gushchin <guro@fb.com>
Subject: writeback, cgroup: add smp_mb() to cgroup_writeback_umount()

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.

Link: https://lkml.kernel.org/r/20210608230225.2078447-3-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Jan Kara <jack@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/fs-writeback.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/fs-writeback.c~writeback-cgroup-add-smp_mb-to-cgroup_writeback_umount
+++ a/fs/fs-writeback.c
@@ -1000,6 +1000,12 @@ out_bdi_put:
  */
 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
_

Patches currently in -mm which might be from guro@fb.com are