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authorNeilBrown <neilb@suse.com>2017-03-15 14:05:14 +1100
committerShaohua Li <shli@fb.com>2017-03-22 19:18:30 -0700
commit55cc39f345256af241deb6152ff5c06bedd10f11 (patch)
tree9d6958f5b6960b3ba9010aa0d23bbe9c3feb5ff2 /drivers/md/md.c
parent6497709b5d1bccce7de1df678d5f147d614551d1 (diff)
md: close a race with setting mddev->in_sync
If ->in_sync is being set just as md_write_start() is being called, it is possible that set_in_sync() won't see the elevated ->writes_pending, and md_write_start() won't see the set ->in_sync. To close this race, re-test ->writes_pending after setting ->in_sync, and add memory barriers to ensure the increment of ->writes_pending will be seen by the time of this second test, or the new ->in_sync will be seen by md_write_start(). Add a spinlock to array_state_show() to ensure this temporary instability is never visible from userspace. Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: Shaohua Li <shli@fb.com>
Diffstat (limited to 'drivers/md/md.c')
-rw-r--r--drivers/md/md.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 5951dea75aba..dee6bbfb29b8 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2258,6 +2258,10 @@ static bool set_in_sync(struct mddev *mddev)
if (atomic_read(&mddev->writes_pending) == 0) {
if (mddev->in_sync == 0) {
mddev->in_sync = 1;
+ smp_mb();
+ if (atomic_read(&mddev->writes_pending))
+ /* lost a race with md_write_start() */
+ mddev->in_sync = 0;
set_bit(MD_SB_CHANGE_CLEAN, &mddev->sb_flags);
sysfs_notify_dirent_safe(mddev->sysfs_state);
}
@@ -4011,6 +4015,7 @@ array_state_show(struct mddev *mddev, char *page)
st = read_auto;
break;
case 0:
+ spin_lock(&mddev->lock);
if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags))
st = write_pending;
else if (mddev->in_sync)
@@ -4019,6 +4024,7 @@ array_state_show(struct mddev *mddev, char *page)
st = active_idle;
else
st = active;
+ spin_unlock(&mddev->lock);
}
else {
if (list_empty(&mddev->disks) &&
@@ -7885,6 +7891,7 @@ void md_write_start(struct mddev *mddev, struct bio *bi)
did_change = 1;
}
atomic_inc(&mddev->writes_pending);
+ smp_mb(); /* Match smp_mb in set_in_sync() */
if (mddev->safemode == 1)
mddev->safemode = 0;
if (mddev->in_sync) {