ocfs2 fix o2dlm dlm run purgelist (rev 3)

This patch fixes 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 <srinivas.eeda@oracle.com>
Acked-by: Sunil Mushran <sunil.mushran@oracle.com>
Cc: stable@kernel.org
Signed-off-by: Joel Becker <joel.becker@oracle.com>

1 files changed, 34 insertions, 46 deletions

diff --git a/fs/ocfs2/dlm/dlmthread.c b/fs/ocfs2/dlm/dlmthread.c
index d4f73ca68fe5..dd78ca3f360f 100644
--- a/fs/ocfs2/dlm/dlmthread.c
+++ b/fs/ocfs2/dlm/dlmthread.c
@@ -152,45 +152,25 @@ 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);
 
         mlog(0, "purging lockres %.*s, master = %d\n", res->lockname.len,
              res->lockname.name, master);
 
         if (!master) {
+                res->state |= DLM_LOCK_RES_DROPPING_REF;
                 /* drop spinlock...  retake below */
+                spin_unlock(&res->spinlock);
                 spin_unlock(&dlm->spinlock);
 
                 spin_lock(&res->spinlock);
@@ -208,31 +188,35 @@ 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);
+        }
+
+        if (!__dlm_lockres_unused(res)) {
+                mlog(ML_ERROR, "found lockres %s:%.*s: in use after deref\n",
+                     dlm->name, res->lockname.len, res->lockname.name);
+                __dlm_print_one_lock_resource(res);
+                BUG();
+        }
 
         __dlm_unhash_lockres(res);
 
         /* 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 +235,7 @@ 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 +247,29 @@ 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, used %d, state %d\n",
+                             dlm->name, lockres->lockname.len,
+                             lockres->lockname.name, !unused, lockres->state);
+                        list_move_tail(&dlm->purge_list, &lockres->purge);
+                        spin_unlock(&lockres->spinlock);
+                        continue;
+                }
+
                 dlm_lockres_get(lockres);
 
-                /* This may drop and reacquire the dlm spinlock if it
-                 * has to do migration. */
-                if (dlm_purge_lockres(dlm, lockres))
-                        BUG();
+                dlm_purge_lockres(dlm, lockres);
 
                 dlm_lockres_put(lockres);