[PATCH 7/6] fs: improve comment in fserror_alloc_event

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

Document the ordering requirements between SB_ACTIVE and
s_pending_errors in the new fserror code.

Cc: jack@suse.cz
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
 fs/fserror.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/fserror.c b/fs/fserror.c
index ec92f5a6db59ce..06ca86adab9b76 100644
--- a/fs/fserror.c
+++ b/fs/fserror.c
@@ -79,6 +79,11 @@ static inline struct fserror_event *fserror_alloc_event(struct super_block *sb,
 	 * If pending_errors already reached zero or is no longer active,
 	 * the superblock is being deactivated so there's no point in
 	 * continuing.
+	 *
+	 * The order of the check of s_pending_errors and SB_ACTIVE are
+	 * mandated by order of accesses in generic_shutdown_super and
+	 * fserror_unmount.  Barriers are implicitly provided by the refcount
+	 * manipulations in this function and fserror_unmount.
 	 */
 	if (!refcount_inc_not_zero(&sb->s_pending_errors))
 		return NULL;