md: always hold reconfig_mutex when calling mddev_suspend()

Most often mddev_suspend() is called with
reconfig_mutex held.  Make this a requirement in
preparation a subsequent patch.  Also require
reconfig_mutex to be held for mddev_resume(),
partly for symmetry and partly to guarantee
no races with incr/decr of mddev->suspend.

Taking the mutex in r5c_disable_writeback_async() is
a little tricky as this is called from a work queue
via log->disable_writeback_work, and flush_work()
is called on that while holding ->reconfig_mutex.
If the work item hasn't run before flush_work()
is called, the work function will not be able to
get the mutex.

So we use mddev_trylock() inside the wait_event() call, and have that
abort when conf->log is set to NULL, which happens before
flush_work() is called.
We wait in mddev->sb_wait and ensure this is woken
when any of the conditions change.  This requires
waking mddev->sb_wait in mddev_unlock().  This is only
like to trigger extra wake_ups of threads that needn't
be woken when metadata is being written, and that
doesn't happen often enough that the cost would be
noticeable.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 252770696a05..8b1d93114f40 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3628,8 +3628,11 @@ static void raid_postsuspend(struct dm_target *ti)
 {
 	struct raid_set *rs = ti->private;
 
-	if (!test_and_set_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags))
+	if (!test_and_set_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags)) {
+		mddev_lock_nointr(&rs->md);
 		mddev_suspend(&rs->md);
+		mddev_unlock(&rs->md);
+	}
 
 	rs->md.ro = 1;
 }
@@ -3886,8 +3889,11 @@ static void raid_resume(struct dm_target *ti)
 	if (!(rs->ctr_flags & RESUME_STAY_FROZEN_FLAGS))
 		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 
-	if (test_and_clear_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags))
+	if (test_and_clear_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags)) {
+		mddev_lock_nointr(mddev);
 		mddev_resume(mddev);
+		mddev_unlock(mddev);
+	}
 }
 
 static struct target_type raid_target = {