Ocfs2 devel - Mar 2016 - [patch 13/25] ocfs2/dlm: fix race between convert and recovery

From: Joseph Qi <joseph.qi at huawei.com>
Subject: ocfs2/dlm: fix race between convert and recovery

There is a race window between dlmconvert_remote and
dlm_move_lockres_to_recovery_list, which will cause a lock with
OCFS2_LOCK_BUSY in grant list, thus system hangs.

dlmconvert_remote
{
        spin_lock(&res->spinlock);
        list_move_tail(&lock->list, &res->converting);
        lock->convert_pending = 1;
        spin_unlock(&res->spinlock);

        status = dlm_send_remote_convert_request();
        >>>>>> race window, master has queued ast and return
DLM_NORMAL,
               and then down before sending ast.
               this node detects master down and calls
               dlm_move_lockres_to_recovery_list, which will revert the
               lock to grant list.
               Then OCFS2_LOCK_BUSY won't be cleared as new master won't
               send ast any more because it thinks already be authorized.

        spin_lock(&res->spinlock);
        lock->convert_pending = 0;
        if (status != DLM_NORMAL)
                dlm_revert_pending_convert(res, lock);
        spin_unlock(&res->spinlock);
}

In this case, check if res->state has DLM_LOCK_RES_RECOVERING bit set (res
is still in recovering) or res master changed (new master has finished
recovery), reset the status to DLM_RECOVERING, then it will retry convert.

Signed-off-by: Joseph Qi <joseph.qi at huawei.com>
Reported-by: Yiwen Jiang <jiangyiwen at huawei.com>
Reviewed-by: Junxiao Bi <junxiao.bi at oracle.com>
Cc: Mark Fasheh <mfasheh at suse.de>
Cc: Joel Becker <jlbec at evilplan.org>
Cc: Tariq Saeed <tariq.x.saeed at oracle.com>
Cc: Junxiao Bi <junxiao.bi at oracle.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
---

 fs/ocfs2/dlm/dlmconvert.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff -puN
fs/ocfs2/dlm/dlmconvert.c~ocfs2-dlm-fix-race-between-convert-and-recovery
fs/ocfs2/dlm/dlmconvert.c
--- a/fs/ocfs2/dlm/dlmconvert.c~ocfs2-dlm-fix-race-between-convert-and-recovery
+++ a/fs/ocfs2/dlm/dlmconvert.c
@@ -262,6 +262,7 @@ enum dlm_status dlmconvert_remote(struct
 				  struct dlm_lock *lock, int flags, int type)
 {
 	enum dlm_status status;
+	u8 old_owner = res->owner;
 
 	mlog(0, "type=%d, convert_type=%d, busy=%d\n", lock->ml.type,
 	     lock->ml.convert_type, res->state & DLM_LOCK_RES_IN_PROGRESS);
@@ -316,11 +317,19 @@ enum dlm_status dlmconvert_remote(struct
 	spin_lock(&res->spinlock);
 	res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
 	lock->convert_pending = 0;
-	/* if it failed, move it back to granted queue */
+	/* if it failed, move it back to granted queue.
+	 * if master returns DLM_NORMAL and then down before sending ast,
+	 * it may have already been moved to granted queue, reset to
+	 * DLM_RECOVERING and retry convert */
 	if (status != DLM_NORMAL) {
 		if (status != DLM_NOTQUEUED)
 			dlm_error(status);
 		dlm_revert_pending_convert(res, lock);
+	} else if ((res->state & DLM_LOCK_RES_RECOVERING) ||
+			(old_owner != res->owner)) {
+		mlog(0, "res %.*s is in recovering or has been recovered.\n",
+				res->lockname.len, res->lockname.name);
+		status = DLM_RECOVERING;
 	}
 bail:
 	spin_unlock(&res->spinlock);
_