[Ocfs2-devel] [PATCH] ocfs2: do not set OCFS2_LOCK_UPCONVERT_FINISHING if nonblocking lock can not be granted at once

[Xue jiufei]

Function ocfs2_readpages() use nonblocking flag to avoid page lock
inversion. It will trigger cluster hang because that flag
OCFS2_LOCK_UPCONVERT_FINISHING is not cleared if nonblocking lock
cannot be granted at once. The flag would prevent dc thread from
downconverting. So other nodes cannot acheive this lockres for ever.

So we should not set OCFS2_LOCK_UPCONVERT_FINISHING when receiving ast
if nonblocking lock had already returned.

Signed-off-by: joyce.xue <xuejiufei at huawei.com>
---
 fs/ocfs2/dlmglue.c | 37 +++++++++++++++++++++++++++++++------
 fs/ocfs2/ocfs2.h   |  6 ++++++
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 21262f2..1ddb6f1 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -861,8 +861,13 @@ static inline void ocfs2_generic_handle_convert_action(struct ocfs2_lock_res *lo
 	 * We set the OCFS2_LOCK_UPCONVERT_FINISHING flag before clearing
 	 * the OCFS2_LOCK_BUSY flag to prevent the dc thread from
 	 * downconverting the lock before the upconvert has fully completed.
+	 * Do not prevent the dc thread from downconverting if NONBLOCK lock
+	 * had already returned.
 	 */
-	lockres_or_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING);
+	if (!(lockres->l_flags & OCFS2_LOCK_NONBLOCK_FINISHED))
+		lockres_or_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING);
+	else
+		lockres_clear_flags(lockres, OCFS2_LOCK_NONBLOCK_FINISHED);
 
 	lockres_clear_flags(lockres, OCFS2_LOCK_BUSY);
 }
@@ -1324,13 +1329,12 @@ static void lockres_add_mask_waiter(struct ocfs2_lock_res *lockres,
 
 /* returns 0 if the mw that was removed was already satisfied, -EBUSY
  * if the mask still hadn't reached its goal */
-static int lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
+static int __lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
 				      struct ocfs2_mask_waiter *mw)
 {
-	unsigned long flags;
 	int ret = 0;
 
-	spin_lock_irqsave(&lockres->l_lock, flags);
+	assert_spin_locked(&lockres->l_lock);
 	if (!list_empty(&mw->mw_item)) {
 		if ((lockres->l_flags & mw->mw_mask) != mw->mw_goal)
 			ret = -EBUSY;
@@ -1338,6 +1342,18 @@ static int lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
 		list_del_init(&mw->mw_item);
 		init_completion(&mw->mw_complete);
 	}
+
+	return ret;
+}
+
+static int lockres_remove_mask_waiter(struct ocfs2_lock_res *lockres,
+				      struct ocfs2_mask_waiter *mw)
+{
+	unsigned long flags;
+	int ret = 0;
+
+	spin_lock_irqsave(&lockres->l_lock, flags);
+	ret = __lockres_remove_mask_waiter(lockres, mw);
 	spin_unlock_irqrestore(&lockres->l_lock, flags);
 
 	return ret;
@@ -1373,6 +1389,7 @@ static int __ocfs2_cluster_lock(struct ocfs2_super *osb,
 	unsigned long flags;
 	unsigned int gen;
 	int noqueue_attempted = 0;
+	int dlm_locked = 0;
 
 	ocfs2_init_mask_waiter(&mw);
 
@@ -1481,6 +1498,7 @@ again:
 			ocfs2_recover_from_dlm_error(lockres, 1);
 			goto out;
 		}
+		dlm_locked = 1;
 
 		mlog(0, "lock %s, successful return from ocfs2_dlm_lock\n",
 		     lockres->l_name);
@@ -1514,10 +1532,17 @@ out:
 	if (wait && arg_flags & OCFS2_LOCK_NONBLOCK &&
 	    mw.mw_mask & (OCFS2_LOCK_BUSY|OCFS2_LOCK_BLOCKED)) {
 		wait = 0;
-		if (lockres_remove_mask_waiter(lockres, &mw))
+		spin_lock_irqsave(&lockres->l_lock, flags);
+		if (__lockres_remove_mask_waiter(lockres, &mw)) {
+			if (dlm_locked)
+				lockres_or_flags(lockres,
+					OCFS2_LOCK_NONBLOCK_FINISHED);
+			spin_unlock_irqrestore(&lockres->l_lock, flags);
 			ret = -EAGAIN;
-		else
+		} else {
+			spin_unlock_irqrestore(&lockres->l_lock, flags);
 			goto again;
+		}
 	}
 	if (wait) {
 		ret = ocfs2_wait_for_mask(&mw);
diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index bbec539..7d6b7d0 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -144,6 +144,12 @@ enum ocfs2_unlock_action {
 						     * before the upconvert
 						     * has completed */
 
+#define OCFS2_LOCK_NONBLOCK_FINISHED (0x00001000) /* NONBLOCK cluster
+						   * lock has already
+						   * returned, do not block
+						   * dc thread from
+						   * downconverting */
+
 struct ocfs2_lock_res_ops;
 
 typedef void (*ocfs2_lock_callback)(int status, unsigned long data);
-- 
1.8.4.3