signals: annotate lock_task_sighand()

lock_task_sighand() grabs sighand->siglock in case of returning non-NULL
but unlock_task_sighand() releases it unconditionally.  This leads sparse
to complain about the lock context imbalance.  Rename and wrap
lock_task_sighand() using __cond_lock() macro to make sparse happy.

Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 393ce94e54b7..3ff5c8519abd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2236,9 +2236,16 @@ static inline void task_unlock(struct task_struct *p)
         spin_unlock(&p->alloc_lock);
 }
 
-extern struct sighand_struct *lock_task_sighand(struct task_struct *tsk,
+extern struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
                                                         unsigned long *flags);
 
+#define lock_task_sighand(tsk, flags)                                   \
+({      struct sighand_struct *__ss;                                    \
+        __cond_lock(&(tsk)->sighand->siglock,                           \
+                    (__ss = __lock_task_sighand(tsk, flags)));          \
+        __ss;                                                           \
+})                                                                      \
+
 static inline void unlock_task_sighand(struct task_struct *tsk,
                                                 unsigned long *flags)
 {
diff --git a/kernel/signal.c b/kernel/signal.c
index 919562c3d6b7..e921409b85a9 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1105,7 +1105,8 @@ int zap_other_threads(struct task_struct *p)
         return count;
 }
 
-struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long *flags)
+struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
+                                           unsigned long *flags)
 {
         struct sighand_struct *sighand;