rtmutex: Handle deadlock detection smarter

Even in the case when deadlock detection is not requested by the
caller, we can detect deadlocks. Right now the code stops the lock
chain walk and keeps the waiter enqueued, even on itself. Silly not to
yell when such a scenario is detected and to keep the waiter enqueued.

Return -EDEADLK unconditionally and handle it at the call sites.

The futex calls return -EDEADLK. The non futex ones dequeue the
waiter, throw a warning and put the task into a schedule loop.

Tagged for stable as it makes the code more robust.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brad Mouring <bmouring@ni.com>
Link: http://lkml.kernel.org/r/20140605152801.836501969@linutronix.de
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/locking/rtmutex-debug.h b/kernel/locking/rtmutex-debug.h
index 14193d596d7858c1db04baeebc55c3e665e01208..ab29b6a2266973662ec43d1b4238b3ef0ce1c126 100644 (file)
--- a/kernel/locking/rtmutex-debug.h
+++ b/kernel/locking/rtmutex-debug.h
@@ -31,3 +31,8 @@ static inline int debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *waiter,
 {
        return (waiter != NULL);
 }
+
+static inline void rt_mutex_print_deadlock(struct rt_mutex_waiter *w)
+{
+       debug_rt_mutex_print_deadlock(w);
+}

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index a620d4d08ca6c17580f0bbb76d7c3ac9129330b9..eb7a4632779861553709d0df2ab2ae00f9a78899 100644 (file)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -314,7 +314,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
                }
                put_task_struct(task);
 
-               return deadlock_detect ? -EDEADLK : 0;
+               return -EDEADLK;
        }
  retry:
        /*
@@ -377,7 +377,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
        if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
                debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
                raw_spin_unlock(&lock->wait_lock);
-               ret = deadlock_detect ? -EDEADLK : 0;
+               ret = -EDEADLK;
                goto out_unlock_pi;
        }
 
@@ -548,7 +548,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
         * which is wrong, as the other waiter is not in a deadlock
         * situation.
         */
-       if (detect_deadlock && owner == task)
+       if (owner == task)
                return -EDEADLK;
 
        raw_spin_lock_irqsave(&task->pi_lock, flags);
@@ -763,6 +763,26 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
        return ret;
 }
 
+static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
+                                    struct rt_mutex_waiter *w)
+{
+       /*
+        * If the result is not -EDEADLOCK or the caller requested
+        * deadlock detection, nothing to do here.
+        */
+       if (res != -EDEADLOCK || detect_deadlock)
+               return;
+
+       /*
+        * Yell lowdly and stop the task right here.
+        */
+       rt_mutex_print_deadlock(w);
+       while (1) {
+               set_current_state(TASK_INTERRUPTIBLE);
+               schedule();
+       }
+}
+
 /*
  * Slow path lock function:
  */
@@ -802,8 +822,10 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
 
        set_current_state(TASK_RUNNING);
 
-       if (unlikely(ret))
+       if (unlikely(ret)) {
                remove_waiter(lock, &waiter);
+               rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
+       }
 
        /*
         * try_to_take_rt_mutex() sets the waiter bit
@@ -1112,7 +1134,8 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
                return 1;
        }
 
-       ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
+       /* We enforce deadlock detection for futexes */
+       ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
 
        if (ret && !rt_mutex_owner(lock)) {
                /*

diff --git a/kernel/locking/rtmutex.h b/kernel/locking/rtmutex.h
index a1a1dd06421d05742e9e5a612b2b010cbdfa096c..f6a1f3c133b12bbd3b0917f712d64f936615af0f 100644 (file)
--- a/kernel/locking/rtmutex.h
+++ b/kernel/locking/rtmutex.h
@@ -24,3 +24,8 @@
 #define debug_rt_mutex_print_deadlock(w)               do { } while (0)
 #define debug_rt_mutex_detect_deadlock(w,d)            (d)
 #define debug_rt_mutex_reset_waiter(w)                 do { } while (0)
+
+static inline void rt_mutex_print_deadlock(struct rt_mutex_waiter *w)
+{
+       WARN(1, "rtmutex deadlock detected\n");
+}