locking/mutex: Initialize mutex_waiter::ww_ctx with poison when debugging

Help catch cases where mutex_lock is used directly on w/w mutexes, which
otherwise result in the w/w tasks reading uninitialized data.

Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-12-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/poison.h b/include/linux/poison.h
index 51334edec506815a70868dd451d5c72944ed0a59..a39540326417960b586cdba4985cf09c131fe086 100644 (file)
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -80,6 +80,7 @@
 /********** kernel/mutexes **********/
 #define MUTEX_DEBUG_INIT       0x11
 #define MUTEX_DEBUG_FREE       0x22
+#define MUTEX_POISON_WW_CTX    ((void *) 0x500 + POISON_POINTER_DELTA)
 
 /********** lib/flex_array.c **********/
 #define FLEX_ARRAY_FREE        0x6c    /* for use-after-free poisoning */

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index cd8598aa04262e741270f185fb3ac688f02707f7..935116723a3d4c06fa5c63369c545a8fdbb07033 100644 (file)
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -785,6 +785,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
        if (!use_ww_ctx) {
                /* add waiting tasks to the end of the waitqueue (FIFO): */
                list_add_tail(&waiter.list, &lock->wait_list);
+
+#ifdef CONFIG_DEBUG_MUTEXES
+               waiter.ww_ctx = MUTEX_POISON_WW_CTX;
+#endif
        } else {
                /* Add in stamp order, waking up waiters that must back off. */
                ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);