Merge remote-tracking branch 'acme/perf/urgent' into perf/core

To pick up fixes.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 14 insertions, 9 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 9ad8dea93dbb..5b2396350dd1 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -413,27 +413,32 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t flags, int override_rlimi
 {
 	struct sigqueue *q = NULL;
 	struct user_struct *user;
+	int sigpending;
 
 	/*
 	 * Protect access to @t credentials. This can go away when all
 	 * callers hold rcu read lock.
+	 *
+	 * NOTE! A pending signal will hold on to the user refcount,
+	 * and we get/put the refcount only when the sigpending count
+	 * changes from/to zero.
 	 */
 	rcu_read_lock();
-	user = get_uid(__task_cred(t)->user);
-	atomic_inc(&user->sigpending);
+	user = __task_cred(t)->user;
+	sigpending = atomic_inc_return(&user->sigpending);
+	if (sigpending == 1)
+		get_uid(user);
 	rcu_read_unlock();
 
-	if (override_rlimit ||
-	    atomic_read(&user->sigpending) <=
-			task_rlimit(t, RLIMIT_SIGPENDING)) {
+	if (override_rlimit || likely(sigpending <= task_rlimit(t, RLIMIT_SIGPENDING))) {
 		q = kmem_cache_alloc(sigqueue_cachep, flags);
 	} else {
 		print_dropped_signal(sig);
 	}
 
 	if (unlikely(q == NULL)) {
-		atomic_dec(&user->sigpending);
-		free_uid(user);
+		if (atomic_dec_and_test(&user->sigpending))
+			free_uid(user);
 	} else {
 		INIT_LIST_HEAD(&q->list);
 		q->flags = 0;
@@ -447,8 +452,8 @@ static void __sigqueue_free(struct sigqueue *q)
 {
 	if (q->flags & SIGQUEUE_PREALLOC)
 		return;
-	atomic_dec(&q->user->sigpending);
-	free_uid(q->user);
+	if (atomic_dec_and_test(&q->user->sigpending))
+		free_uid(q->user);
 	kmem_cache_free(sigqueue_cachep, q);
 }