staging/lustre/clio: Solve a race in cl_lock_put

It's not atomic to check the last reference and state of cl_lock
in cl_lock_put(). This can cause a problem that an using lock is
freed, if the process is preempted between atomic_dec_and_test()
and (lock->cll_state == CLS_FREEING).

This problem can be solved by holding a refcount by coh_locks. In
this case, it can be sure that if the lock refcount reaches zero,
nobody else can have any chance to use it again.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-on: http://review.whamcloud.com/9881
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4558
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/lustre/lustre/obdclass/cl_lock.c b/drivers/staging/lustre/lustre/obdclass/cl_lock.c
index 918f433b22d94fcac55d937f1b0e2049f78cfe4e..f8040a8923b27eb284a741673f4be6c2bbcd38fb 100644 (file)
--- a/drivers/staging/lustre/lustre/obdclass/cl_lock.c
+++ b/drivers/staging/lustre/lustre/obdclass/cl_lock.c
@@ -533,6 +533,7 @@ static struct cl_lock *cl_lock_find(const struct lu_env *env,
                        spin_lock(&head->coh_lock_guard);
                        ghost = cl_lock_lookup(env, obj, io, need);
                        if (ghost == NULL) {
+                               cl_lock_get_trust(lock);
                                list_add_tail(&lock->cll_linkage,
                                                  &head->coh_locks);
                                spin_unlock(&head->coh_lock_guard);
@@ -791,15 +792,22 @@ static void cl_lock_delete0(const struct lu_env *env, struct cl_lock *lock)
        LINVRNT(cl_lock_invariant(env, lock));
 
        if (lock->cll_state < CLS_FREEING) {
+               bool in_cache;
+
                LASSERT(lock->cll_state != CLS_INTRANSIT);
                cl_lock_state_set(env, lock, CLS_FREEING);
 
                head = cl_object_header(lock->cll_descr.cld_obj);
 
                spin_lock(&head->coh_lock_guard);
-               list_del_init(&lock->cll_linkage);
+               in_cache = !list_empty(&lock->cll_linkage);
+               if (in_cache)
+                       list_del_init(&lock->cll_linkage);
                spin_unlock(&head->coh_lock_guard);
 
+               if (in_cache) /* coh_locks cache holds a refcount. */
+                       cl_lock_put(env, lock);
+
                /*
                 * From now on, no new references to this lock can be acquired
                 * by cl_lock_lookup().