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-rw-r--r--kernel/ipc/msg.c2
-rw-r--r--kernel/ipc/sem.c142
2 files changed, 82 insertions, 62 deletions
diff --git a/kernel/ipc/msg.c b/kernel/ipc/msg.c
index b8c5e7f2b..996d89023 100644
--- a/kernel/ipc/msg.c
+++ b/kernel/ipc/msg.c
@@ -666,7 +666,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
rcu_read_lock();
ipc_lock_object(&msq->q_perm);
- ipc_rcu_putref(msq, ipc_rcu_free);
+ ipc_rcu_putref(msq, msg_rcu_free);
/* raced with RMID? */
if (!ipc_valid_object(&msq->q_perm)) {
err = -EIDRM;
diff --git a/kernel/ipc/sem.c b/kernel/ipc/sem.c
index dc67f53c0..ef34d7376 100644
--- a/kernel/ipc/sem.c
+++ b/kernel/ipc/sem.c
@@ -155,14 +155,21 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
/*
* Locking:
+ * a) global sem_lock() for read/write
* sem_undo.id_next,
* sem_array.complex_count,
- * sem_array.pending{_alter,_cont},
- * sem_array.sem_undo: global sem_lock() for read/write
- * sem_undo.proc_next: only "current" is allowed to read/write that field.
+ * sem_array.complex_mode
+ * sem_array.pending{_alter,_const},
+ * sem_array.sem_undo
*
+ * b) global or semaphore sem_lock() for read/write:
* sem_array.sem_base[i].pending_{const,alter}:
- * global or semaphore sem_lock() for read/write
+ * sem_array.complex_mode (for read)
+ *
+ * c) special:
+ * sem_undo_list.list_proc:
+ * * undo_list->lock for write
+ * * rcu for read
*/
#define sc_semmsl sem_ctls[0]
@@ -263,24 +270,25 @@ static void sem_rcu_free(struct rcu_head *head)
#define ipc_smp_acquire__after_spin_is_unlocked() smp_rmb()
/*
- * Wait until all currently ongoing simple ops have completed.
+ * Enter the mode suitable for non-simple operations:
* Caller must own sem_perm.lock.
- * New simple ops cannot start, because simple ops first check
- * that sem_perm.lock is free.
- * that a) sem_perm.lock is free and b) complex_count is 0.
*/
-static void sem_wait_array(struct sem_array *sma)
+static void complexmode_enter(struct sem_array *sma)
{
int i;
struct sem *sem;
- if (sma->complex_count) {
- /* The thread that increased sma->complex_count waited on
- * all sem->lock locks. Thus we don't need to wait again.
- */
+ if (sma->complex_mode) {
+ /* We are already in complex_mode. Nothing to do */
return;
}
+ /* We need a full barrier after seting complex_mode:
+ * The write to complex_mode must be visible
+ * before we read the first sem->lock spinlock state.
+ */
+ smp_store_mb(sma->complex_mode, true);
+
for (i = 0; i < sma->sem_nsems; i++) {
sem = sma->sem_base + i;
spin_unlock_wait(&sem->lock);
@@ -289,6 +297,28 @@ static void sem_wait_array(struct sem_array *sma)
}
/*
+ * Try to leave the mode that disallows simple operations:
+ * Caller must own sem_perm.lock.
+ */
+static void complexmode_tryleave(struct sem_array *sma)
+{
+ if (sma->complex_count) {
+ /* Complex ops are sleeping.
+ * We must stay in complex mode
+ */
+ return;
+ }
+ /*
+ * Immediately after setting complex_mode to false,
+ * a simple op can start. Thus: all memory writes
+ * performed by the current operation must be visible
+ * before we set complex_mode to false.
+ */
+ smp_store_release(&sma->complex_mode, false);
+}
+
+#define SEM_GLOBAL_LOCK (-1)
+/*
* If the request contains only one semaphore operation, and there are
* no complex transactions pending, lock only the semaphore involved.
* Otherwise, lock the entire semaphore array, since we either have
@@ -304,56 +334,42 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
/* Complex operation - acquire a full lock */
ipc_lock_object(&sma->sem_perm);
- /* And wait until all simple ops that are processed
- * right now have dropped their locks.
- */
- sem_wait_array(sma);
- return -1;
+ /* Prevent parallel simple ops */
+ complexmode_enter(sma);
+ return SEM_GLOBAL_LOCK;
}
/*
* Only one semaphore affected - try to optimize locking.
- * The rules are:
- * - optimized locking is possible if no complex operation
- * is either enqueued or processed right now.
- * - The test for enqueued complex ops is simple:
- * sma->complex_count != 0
- * - Testing for complex ops that are processed right now is
- * a bit more difficult. Complex ops acquire the full lock
- * and first wait that the running simple ops have completed.
- * (see above)
- * Thus: If we own a simple lock and the global lock is free
- * and complex_count is now 0, then it will stay 0 and
- * thus just locking sem->lock is sufficient.
+ * Optimized locking is possible if no complex operation
+ * is either enqueued or processed right now.
+ *
+ * Both facts are tracked by complex_mode.
*/
sem = sma->sem_base + sops->sem_num;
- if (sma->complex_count == 0) {
+ /*
+ * Initial check for complex_mode. Just an optimization,
+ * no locking, no memory barrier.
+ */
+ if (!sma->complex_mode) {
/*
* It appears that no complex operation is around.
* Acquire the per-semaphore lock.
*/
spin_lock(&sem->lock);
- /* Then check that the global lock is free */
- if (!spin_is_locked(&sma->sem_perm.lock)) {
- /*
- * We need a memory barrier with acquire semantics,
- * otherwise we can race with another thread that does:
- * complex_count++;
- * spin_unlock(sem_perm.lock);
- */
- ipc_smp_acquire__after_spin_is_unlocked();
+ /*
+ * See 51d7d5205d33
+ * ("powerpc: Add smp_mb() to arch_spin_is_locked()"):
+ * A full barrier is required: the write of sem->lock
+ * must be visible before the read is executed
+ */
+ smp_mb();
- /*
- * Now repeat the test of complex_count:
- * It can't change anymore until we drop sem->lock.
- * Thus: if is now 0, then it will stay 0.
- */
- if (sma->complex_count == 0) {
- /* fast path successful! */
- return sops->sem_num;
- }
+ if (!smp_load_acquire(&sma->complex_mode)) {
+ /* fast path successful! */
+ return sops->sem_num;
}
spin_unlock(&sem->lock);
}
@@ -373,15 +389,16 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
/* Not a false alarm, thus complete the sequence for a
* full lock.
*/
- sem_wait_array(sma);
- return -1;
+ complexmode_enter(sma);
+ return SEM_GLOBAL_LOCK;
}
}
static inline void sem_unlock(struct sem_array *sma, int locknum)
{
- if (locknum == -1) {
+ if (locknum == SEM_GLOBAL_LOCK) {
unmerge_queues(sma);
+ complexmode_tryleave(sma);
ipc_unlock_object(&sma->sem_perm);
} else {
struct sem *sem = sma->sem_base + locknum;
@@ -442,7 +459,7 @@ static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns
static inline void sem_lock_and_putref(struct sem_array *sma)
{
sem_lock(sma, NULL, -1);
- ipc_rcu_putref(sma, ipc_rcu_free);
+ ipc_rcu_putref(sma, sem_rcu_free);
}
static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
@@ -533,6 +550,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
}
sma->complex_count = 0;
+ sma->complex_mode = true; /* dropped by sem_unlock below */
INIT_LIST_HEAD(&sma->pending_alter);
INIT_LIST_HEAD(&sma->pending_const);
INIT_LIST_HEAD(&sma->list_id);
@@ -1395,7 +1413,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
rcu_read_unlock();
sem_io = ipc_alloc(sizeof(ushort)*nsems);
if (sem_io == NULL) {
- ipc_rcu_putref(sma, ipc_rcu_free);
+ ipc_rcu_putref(sma, sem_rcu_free);
return -ENOMEM;
}
@@ -1429,20 +1447,20 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
if (nsems > SEMMSL_FAST) {
sem_io = ipc_alloc(sizeof(ushort)*nsems);
if (sem_io == NULL) {
- ipc_rcu_putref(sma, ipc_rcu_free);
+ ipc_rcu_putref(sma, sem_rcu_free);
return -ENOMEM;
}
}
if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) {
- ipc_rcu_putref(sma, ipc_rcu_free);
+ ipc_rcu_putref(sma, sem_rcu_free);
err = -EFAULT;
goto out_free;
}
for (i = 0; i < nsems; i++) {
if (sem_io[i] > SEMVMX) {
- ipc_rcu_putref(sma, ipc_rcu_free);
+ ipc_rcu_putref(sma, sem_rcu_free);
err = -ERANGE;
goto out_free;
}
@@ -1732,7 +1750,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
/* step 2: allocate new undo structure */
new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
if (!new) {
- ipc_rcu_putref(sma, ipc_rcu_free);
+ ipc_rcu_putref(sma, sem_rcu_free);
return ERR_PTR(-ENOMEM);
}
@@ -2196,10 +2214,10 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
/*
* The proc interface isn't aware of sem_lock(), it calls
* ipc_lock_object() directly (in sysvipc_find_ipc).
- * In order to stay compatible with sem_lock(), we must wait until
- * all simple semop() calls have left their critical regions.
+ * In order to stay compatible with sem_lock(), we must
+ * enter / leave complex_mode.
*/
- sem_wait_array(sma);
+ complexmode_enter(sma);
sem_otime = get_semotime(sma);
@@ -2216,6 +2234,8 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
sem_otime,
sma->sem_ctime);
+ complexmode_tryleave(sma);
+
return 0;
}
#endif