Kernel bump from 4.1.3-rt to 4.1.7-rt.

[kvmfornfv.git] / kernel / ipc / sem.c

diff --git a/kernel/ipc/sem.c b/kernel/ipc/sem.c
index 8f99bac..d6261be 100644 (file)
--- a/kernel/ipc/sem.c
+++ b/kernel/ipc/sem.c
@@ -252,6 +252,16 @@ static void sem_rcu_free(struct rcu_head *head)
        ipc_rcu_free(head);
 }
 
+/*
+ * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
+ * are only control barriers.
+ * The code must pair with spin_unlock(&sem->lock) or
+ * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient.
+ *
+ * smp_rmb() is sufficient, as writes cannot pass the control barrier.
+ */
+#define ipc_smp_acquire__after_spin_is_unlocked()      smp_rmb()
+
 /*
  * Wait until all currently ongoing simple ops have completed.
  * Caller must own sem_perm.lock.
@@ -275,6 +285,7 @@ static void sem_wait_array(struct sem_array *sma)
                sem = sma->sem_base + i;
                spin_unlock_wait(&sem->lock);
        }
+       ipc_smp_acquire__after_spin_is_unlocked();
 }
 
 /*
@@ -327,13 +338,12 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
                /* Then check that the global lock is free */
                if (!spin_is_locked(&sma->sem_perm.lock)) {
                        /*
-                        * The ipc object lock check must be visible on all
-                        * cores before rechecking the complex count.  Otherwise
-                        * we can race with  another thread that does:
+                        * We need a memory barrier with acquire semantics,
+                        * otherwise we can race with another thread that does:
                         *      complex_count++;
                         *      spin_unlock(sem_perm.lock);
                         */
-                       smp_rmb();
+                       ipc_smp_acquire__after_spin_is_unlocked();
 
                        /*
                         * Now repeat the test of complex_count:
@@ -2084,17 +2094,28 @@ void exit_sem(struct task_struct *tsk)
                rcu_read_lock();
                un = list_entry_rcu(ulp->list_proc.next,
                                    struct sem_undo, list_proc);
-               if (&un->list_proc == &ulp->list_proc)
-                       semid = -1;
-                else
-                       semid = un->semid;
+               if (&un->list_proc == &ulp->list_proc) {
+                       /*
+                        * We must wait for freeary() before freeing this ulp,
+                        * in case we raced with last sem_undo. There is a small
+                        * possibility where we exit while freeary() didn't
+                        * finish unlocking sem_undo_list.
+                        */
+                       spin_unlock_wait(&ulp->lock);
+                       rcu_read_unlock();
+                       break;
+               }
+               spin_lock(&ulp->lock);
+               semid = un->semid;
+               spin_unlock(&ulp->lock);
 
+               /* exit_sem raced with IPC_RMID, nothing to do */
                if (semid == -1) {
                        rcu_read_unlock();
-                       break;
+                       continue;
                }
 
-               sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->semid);
+               sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid);
                /* exit_sem raced with IPC_RMID, nothing to do */
                if (IS_ERR(sma)) {
                        rcu_read_unlock();