From: Vitaly Fertman <vitaly_fertman@xyratex.com>
Date: Mon, 17 Dec 2012 19:48:44 +0000 (+0400)
Subject: LU-2317 mgs: both callbacks are to be fixed
X-Git-Tag: 2.3.59~48
X-Git-Url: https://git.whamcloud.com/?p=fs%2Flustre-release.git;a=commitdiff_plain;h=df7c3d41c67674df4fe137084ed8afedd3be89aa

LU-2317 mgs: both callbacks are to be fixed

The commit ORNL-27 introduced a new lock enqueue which drops a
reference on it in the blocking callbacks. however, it turned out
to be racy as if a lock is taken quickly, callback is called twice,
from enqueue completion and from conflicting lock cancel, and lock
reference is decremented twice.  LU-1259 tried to fix it, but only
for 1 callback.

Fix it for mgs_completion_ast_config as well.

Signed-off-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Xyratex-bug-id: MRP-792
Change-Id: I49207cfae230318da3b6dcbe3a63c14d8d94a244
Reviewed-on: http://review.whamcloud.com/4744
Tested-by: Hudson
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
---

diff --git a/lustre/mgs/mgs_handler.c b/lustre/mgs/mgs_handler.c
index dc993c7..ae68653 100644
--- a/lustre/mgs/mgs_handler.c
+++ b/lustre/mgs/mgs_handler.c
@@ -132,23 +132,33 @@ static int mgs_disconnect(struct obd_export *exp)
 static int mgs_handle(struct ptlrpc_request *req);
 
 static int mgs_completion_ast_config(struct ldlm_lock *lock, __u64 flags,
-                                     void *cbdata)
+				     void *cbdata)
 {
-        ENTRY;
+	ENTRY;
 
-        if (!(flags & (LDLM_FL_BLOCK_WAIT | LDLM_FL_BLOCK_GRANTED |
-                       LDLM_FL_BLOCK_CONV))) {
-                struct fs_db *fsdb = (struct fs_db *)lock->l_ast_data;
-                struct lustre_handle lockh;
+	if (!(flags & (LDLM_FL_BLOCK_WAIT | LDLM_FL_BLOCK_GRANTED |
+		       LDLM_FL_BLOCK_CONV))) {
+                struct fs_db *fsdb;
 
-                /* clear the bit before lock put */
-		clear_bit(FSDB_REVOKING_LOCK, &fsdb->fsdb_flags);
+		/* l_ast_data is used as a marker to avoid cancel ldlm lock
+		 * twice. See LU-2317. */
+		lock_res_and_lock(lock);
+		fsdb = (struct fs_db *)lock->l_ast_data;
+		lock->l_ast_data = NULL;
+		unlock_res_and_lock(lock);
 
-                ldlm_lock2handle(lock, &lockh);
-                ldlm_lock_decref_and_cancel(&lockh, LCK_EX);
-        }
+		if (fsdb != NULL) {
+			struct lustre_handle lockh;
 
-        RETURN(ldlm_completion_ast(lock, flags, cbdata));
+			/* clear the bit before lock put */
+			clear_bit(FSDB_REVOKING_LOCK, &fsdb->fsdb_flags);
+
+			ldlm_lock2handle(lock, &lockh);
+			ldlm_lock_decref_and_cancel(&lockh, LCK_EX);
+		}
+	}
+
+	RETURN(ldlm_completion_ast(lock, flags, cbdata));
 }
 
 static int mgs_completion_ast_ir(struct ldlm_lock *lock, __u64 flags,