locking/mutex: Fix debug checks
OK, so commit:
1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")
generates this boot warning when CONFIG_DEBUG_MUTEXES=y:
WARNING: CPU: 0 PID: 139 at /usr/src/linux-2.6/kernel/locking/mutex-debug.c:82 debug_mutex_unlock+0x155/0x180() DEBUG_LOCKS_WARN_ON(lock->owner != current)
And that makes sense, because as soon as we release the lock a
new owner can come in...
One would think that !__mutex_slowpath_needs_to_unlock()
implementations suffer the same, but for DEBUG we fall back to
mutex-null.h which has an unconditional 1 for that.
The mutex debug code requires the mutex to be unlocked after
doing the debug checks, otherwise it can find inconsistent
state.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: jason.low2@hp.com
Link: http://lkml.kernel.org/r/20140312122442.GB27965@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index faf6f5b..e1191c9 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -83,6 +83,12 @@
DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
mutex_clear_owner(lock);
+
+ /*
+ * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug
+ * mutexes so that we can do it here after we've verified state.
+ */
+ atomic_set(&lock->count, 1);
}
void debug_mutex_init(struct mutex *lock, const char *name,
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 02c61a9..14fe72c 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -34,6 +34,13 @@
#ifdef CONFIG_DEBUG_MUTEXES
# include "mutex-debug.h"
# include <asm-generic/mutex-null.h>
+/*
+ * Must be 0 for the debug case so we do not do the unlock outside of the
+ * wait_lock region. debug_mutex_unlock() will do the actual unlock in this
+ * case.
+ */
+# undef __mutex_slowpath_needs_to_unlock
+# define __mutex_slowpath_needs_to_unlock() 0
#else
# include "mutex.h"
# include <asm/mutex.h>