From: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Date: Mon, 21 Jan 2013 21:15:23 +0000 (+0200)
Subject: LU-1602 ldlm: Fix flock deadlock detection race
X-Git-Tag: 2.4.51~3
X-Git-Url: https://git.whamcloud.com/?p=fs%2Flustre-release.git;a=commitdiff_plain;h=bbe7043202fa9750369e7f027f1b96393b49b1dc

LU-1602 ldlm: Fix flock deadlock detection race

Deadlock isn't detected if 2 threads are trying to
grant 2 locks which deadlock on each other.
They call ldlm_flock_deadlock() simultaneously
and deadlock ins't detected.

The soulition is to add lock to blocking list before
calling ldlm_flock_deadlock()

Xyratex-bug-id: MRP-412
Signed-off-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Reviewed-by: Bruce Korb <bruce_korb@xyratex.com>
Change-Id: I437c8b40a58de14bbac3da39d98d0f03d0f2e064
Reviewed-on: http://review.whamcloud.com/3277
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
---

diff --git a/lustre/ldlm/ldlm_flock.c b/lustre/ldlm/ldlm_flock.c
index c880dc0..5b40b3e 100644
--- a/lustre/ldlm/ldlm_flock.c
+++ b/lustre/ldlm/ldlm_flock.c
@@ -203,6 +203,7 @@ ldlm_flock_deadlock(struct ldlm_lock *req, struct ldlm_lock *bl_lock)
 		if (lock == NULL)
 			break;
 
+		LASSERT(req != lock);
 		flock = &lock->l_policy_data.l_flock;
 		LASSERT(flock->owner == bl_owner);
                 bl_owner = flock->blocking_owner;
@@ -334,18 +335,21 @@ reprocess:
                                 RETURN(LDLM_ITER_STOP);
                         }
 
-                        if (ldlm_flock_deadlock(req, lock)) {
-                                ldlm_flock_destroy(req, mode, *flags);
-                                *err = -EDEADLK;
-                                RETURN(LDLM_ITER_STOP);
-                        }
-
+			/* add lock to blocking list before deadlock
+			 * check to prevent race */
 			rc = ldlm_flock_blocking_link(req, lock);
 			if (rc) {
 				ldlm_flock_destroy(req, mode, *flags);
 				*err = rc;
 				RETURN(LDLM_ITER_STOP);
 			}
+			if (ldlm_flock_deadlock(req, lock)) {
+				ldlm_flock_blocking_unlink(req);
+				ldlm_flock_destroy(req, mode, *flags);
+				*err = -EDEADLK;
+				RETURN(LDLM_ITER_STOP);
+			}
+
                         ldlm_resource_add_lock(res, &res->lr_waiting, req);
                         *flags |= LDLM_FL_BLOCK_GRANTED;
                         RETURN(LDLM_ITER_STOP);