[PATCH RT 28/36] locking: ww_mutex: fix ww_mutex vs self-deadlock

Steven Rostedt
2015-03-12T19:26:20Z

[-- Attachment #1: 0028-locking-ww_mutex-fix-ww_mutex-vs-self-deadlock.patch --]
[-- Type: text/plain, Size: 3158 bytes --]

3.12.38-rt53-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Mike Galbraith <umgwanakikbuti@gmail.com>

If the caller already holds the mutex, task_blocks_on_rt_mutex()
returns -EDEADLK, we proceed directly to rt_mutex_handle_deadlock()
where it's instant game over.

Let ww_mutexes return EDEADLK/EALREADY as they want to instead.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/rtmutex.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index e8a6555a670a..7601c1332a88 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -1621,13 +1621,20 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,

if (likely(!ret))
ret = __rt_mutex_slowlock(lock, state, timeout, &waiter, ww_ctx);
+ else if (ww_ctx) {
+ /* ww_mutex received EDEADLK, let it become EALREADY */
+ ret = __mutex_lock_check_stamp(lock, ww_ctx);
+ BUG_ON(!ret);
+ }

set_current_state(TASK_RUNNING);

if (unlikely(ret)) {
if (rt_mutex_has_waiters(lock))
remove_waiter(lock, &waiter);
- rt_mutex_handle_deadlock(ret, chwalk, &waiter);
+ /* ww_mutex want to report EDEADLK/EALREADY, let them */
+ if (!ww_ctx)
+ rt_mutex_handle_deadlock(ret, chwalk, &waiter);
} else if (ww_ctx) {
ww_mutex_account_lock(lock, ww_ctx);
}
@@ -2166,8 +2173,7 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ww_c
might_sleep();

mutex_acquire_nest(&lock->base.dep_map, 0, 0, &ww_ctx->dep_map, _RET_IP_);
- ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL,
- RT_MUTEX_FULL_CHAINWALK, ww_ctx);
+ ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL, 0, ww_ctx);
if (ret)
mutex_release(&lock->base.dep_map, 1, _RET_IP_);
else if (!ret && ww_ctx->acquired > 1)
@@ -2185,8 +2191,7 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx)
might_sleep();

mutex_acquire_nest(&lock->base.dep_map, 0, 0, &ww_ctx->dep_map, _RET_IP_);
- ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL,
- RT_MUTEX_FULL_CHAINWALK, ww_ctx);
+ ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL, 0, ww_ctx);
if (ret)
mutex_release(&lock->base.dep_map, 1, _RET_IP_);
else if (!ret && ww_ctx->acquired > 1)
@@ -2198,11 +2203,13 @@ EXPORT_SYMBOL_GPL(__ww_mutex_lock);

void __sched ww_mutex_unlock(struct ww_mutex *lock)
{
+ int nest = !!lock->ctx;
+
/*
* The unlocking fastpath is the 0->1 transition from 'locked'
* into 'unlocked' state:
*/
- if (lock->ctx) {
+ if (nest) {
#ifdef CONFIG_DEBUG_MUTEXES
DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
#endif
@@ -2211,7 +2218,7 @@ void __sched ww_mutex_unlock(struct ww_mutex *lock)
lock->ctx = NULL;
}

- mutex_release(&lock->base.dep_map, 1, _RET_IP_);
+ mutex_release(&lock->base.dep_map, nest, _RET_IP_);
rt_mutex_unlock(&lock->base.lock);
}
EXPORT_SYMBOL(ww_mutex_unlock);
--
2.1.4