ocfs2 fix o2dlm dlm run purgelist(bug 9094491) - rev3

There are two problems in dlm_run_purgelist

1. If a lockres is found to be in use, dlm_run_purgelist keeps trying to purge the same lockres instead of trying the next lockres.

2. When a lockres is found unused, dlm_run_purgelist releases lockres spinlock before setting DLM_LOCK_RES_DROPPING_REF and calls dlm_purge_lockres. spinlock is reacquired but in this window lockres can get reused. This leads to BUG.

This patch modifies dlm_run_purgelist to skip lockres if it's in use and purge
next lockres. It also sets DLM_LOCK_RES_DROPPING_REF before releasing the
lockres spinlock protecting it from getting reused.

Signed-off-by Srinivas Eeda<[email protected]>

---
  fs/ocfs2/dlm/dlmthread.c |   76 ++++++++++++++++++++--------------------------
  1 files changed, 33 insertions(+), 43 deletions(-)

fs/ocfs2/dlm/dlmthread.c +3 -23

index 11a6d1f..cb74689 100644
@@ -152,45 +152,26 @@ void dlm_lockres_calc_usage(struct dlm_ctxt *dlm,
  	spin_unlock(&dlm->spinlock);
  }
 
-static int dlm_purge_lockres(struct dlm_ctxt *dlm,
+static void dlm_purge_lockres(struct dlm_ctxt *dlm,
  			     struct dlm_lock_resource *res)
  {
  	int master;
  	int ret = 0;
 
-	spin_lock(&res->spinlock);
-	if (!__dlm_lockres_unused(res)) {
-		mlog(0, "%s:%.*s: tried to purge but not unused\n",
-		     dlm->name, res->lockname.len, res->lockname.name);
-		__dlm_print_one_lock_resource(res);
-		spin_unlock(&res->spinlock);
-		BUG();
-	}
-
-	if (res->state&  DLM_LOCK_RES_MIGRATING) {
-		mlog(0, "%s:%.*s: Delay dropref as this lockres is "
-		     "being remastered\n", dlm->name, res->lockname.len,
-		     res->lockname.name);
-		/* Re-add the lockres to the end of the purge list */
-		if (!list_empty(&res->purge)) {
-			list_del_init(&res->purge);
-			list_add_tail(&res->purge,&dlm->purge_list);
-		}
-		spin_unlock(&res->spinlock);
-		return 0;
-	}
+	assert_spin_locked(&dlm->spinlock);
+	assert_spin_locked(&res->spinlock);
 
  	master = (res->owner == dlm->node_num);
 
  	if (!master)
  		res->state |= DLM_LOCK_RES_DROPPING_REF;
-	spin_unlock(&res->spinlock);

fs/ocfs2/dlm/dlmthread.c +2 -4

@@ -208,31 +189,35 @@ static int dlm_purge_lockres(struct dlm_ctxt *dlm,
  		mlog(0, "%s:%.*s: dlm_deref_lockres returned %d\n",
  		     dlm->name, res->lockname.len, res->lockname.name, ret);
  		spin_lock(&dlm->spinlock);
+		spin_lock(&res->spinlock);
  	}
 
-	spin_lock(&res->spinlock);
  	if (!list_empty(&res->purge)) {
  		mlog(0, "removing lockres %.*s:%p from purgelist, "
  		     "master = %d\n", res->lockname.len, res->lockname.name,
  		     res, master);
  		list_del_init(&res->purge);
-		spin_unlock(&res->spinlock);
  		dlm_lockres_put(res);
  		dlm->purge_count--;
-	} else
-		spin_unlock(&res->spinlock);
+	}
 

fs/ocfs2/dlm/dlmthread.c +18 -13

  	/* lockres is not in the hash now.  drop the flag and wake up
  	 * any processes waiting in dlm_get_lock_resource. */
  	if (!master) {
-		spin_lock(&res->spinlock);
  		res->state&= ~DLM_LOCK_RES_DROPPING_REF;
  		spin_unlock(&res->spinlock);
  		wake_up(&res->wq);
-	}
-	return 0;
+	} else
+		spin_unlock(&res->spinlock);
  }
 
  static void dlm_run_purge_list(struct dlm_ctxt *dlm,

@@ -251,17 +236,7 @@ static void dlm_run_purge_list(struct dlm_ctxt *dlm,
  		lockres = list_entry(dlm->purge_list.next,
  				     struct dlm_lock_resource, purge);
 
-		/* Status of the lockres *might* change so double
-		 * check. If the lockres is unused, holding the dlm
-		 * spinlock will prevent people from getting and more
-		 * refs on it -- there's no need to keep the lockres
-		 * spinlock. */
  		spin_lock(&lockres->spinlock);
-		unused = __dlm_lockres_unused(lockres);
-		spin_unlock(&lockres->spinlock);
-
-		if (!unused)
-			continue;
 
  		purge_jiffies = lockres->last_used +
  			msecs_to_jiffies(DLM_PURGE_INTERVAL_MS);

@@ -273,15 +248,30 @@ static void dlm_run_purge_list(struct dlm_ctxt *dlm,
  			 * in tail order, we can stop at the first
  			 * unpurgable resource -- anyone added after
  			 * him will have a greater last_used value */
+			spin_unlock(&lockres->spinlock);
  			break;
  		}
 
+		/* Status of the lockres *might* change so double
+		 * check. If the lockres is unused, holding the dlm
+		 * spinlock will prevent people from getting and more
+		 * refs on it. */
+		unused = __dlm_lockres_unused(lockres);
+		if (!unused ||
+		    (lockres->state&  DLM_LOCK_RES_MIGRATING)) {
+			mlog(0, "lockres %s:%.*s: is in use or "
+			     "being remastered\n", dlm->name,
+			     lockres->lockname.len, lockres->lockname.name);
+			list_move_tail(&dlm->purge_list,&lockres->purge);
+			spin_unlock(&lockres->spinlock);
+			continue;
+		}
+