From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
tglx@linutronix.de, jason.low2@hp.com
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:core/locking] locking/mutexes: Unlock the mutex without the wait_lock
Date: Wed, 12 Mar 2014 13:24:42 +0100 [thread overview]
Message-ID: <20140312122442.GB27965@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <tip-1d8fe7dc8078b23e060ec62ccb4cdc1ac3c41bf8@git.kernel.org>
On Tue, Mar 11, 2014 at 05:41:23AM -0700, tip-bot for Jason Low wrote:
> kernel/locking/mutex.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index 82dad2c..dc3d6f2 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -671,10 +671,6 @@ __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
> struct mutex *lock = container_of(lock_count, struct mutex, count);
> unsigned long flags;
>
> - spin_lock_mutex(&lock->wait_lock, flags);
> - mutex_release(&lock->dep_map, nested, _RET_IP_);
> - debug_mutex_unlock(lock);
> -
> /*
> * some architectures leave the lock unlocked in the fastpath failure
> * case, others need to leave it locked. In the later case we have to
> @@ -683,6 +679,10 @@ __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
> if (__mutex_slowpath_needs_to_unlock())
> atomic_set(&lock->count, 1);
>
> + spin_lock_mutex(&lock->wait_lock, flags);
> + mutex_release(&lock->dep_map, nested, _RET_IP_);
> + debug_mutex_unlock(lock);
> +
> if (!list_empty(&lock->wait_list)) {
> /* get the first entry from the wait-list: */
> struct mutex_waiter *waiter =
OK, so this patch generates:
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)
for kernels with CONFIG_DEBUG_MUTEXES=y
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.
How about something like the below; will test after lunch.
---
Subject: locking/mutex: Fix debug checks
The mutex debug code requires the mutex to be unlocked after doing the
debug checks, otherwise it can find inconsistent state.
Fixes: 1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")
Almost-Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
kernel/locking/mutex-debug.c | 6 ++++++
kernel/locking/mutex.c | 7 +++++++
2 files changed, 13 insertions(+)
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index faf6f5b53e77..e1191c996c59 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -83,6 +83,12 @@ void debug_mutex_unlock(struct mutex *lock)
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 26c96142caac..e6fa88b64b17 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>
next prev parent reply other threads:[~2014-03-12 12:24 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-28 19:13 [PATCH v2 0/5] mutex: Mutex scalability patches Jason Low
2014-01-28 19:13 ` [PATCH v2 1/5] mutex: In mutex_can_spin_on_owner(), return false if task need_resched() Jason Low
2014-01-28 20:20 ` Paul E. McKenney
2014-01-28 22:01 ` Jason Low
2014-01-28 21:09 ` Davidlohr Bueso
2014-03-11 12:41 ` [tip:core/locking] locking/mutexes: Return false if task need_resched() in mutex_can_spin_on_owner() tip-bot for Jason Low
2014-01-28 19:13 ` [PATCH v2 2/5] mutex: Modify the way optimistic spinners are queued Jason Low
2014-01-28 20:23 ` Paul E. McKenney
2014-01-28 20:24 ` Paul E. McKenney
2014-01-28 21:17 ` Davidlohr Bueso
2014-01-28 22:10 ` Jason Low
2014-02-02 21:58 ` Paul E. McKenney
2014-03-11 12:41 ` [tip:core/locking] locking/mutexes: " tip-bot for Jason Low
2014-03-11 15:24 ` Jason Low
2014-03-11 15:33 ` Peter Zijlstra
2014-01-28 19:13 ` [PATCH v2 3/5] mutex: Unlock the mutex without the wait_lock Jason Low
2014-03-11 12:41 ` [tip:core/locking] locking/mutexes: " tip-bot for Jason Low
2014-03-12 12:24 ` Peter Zijlstra [this message]
2014-03-12 18:44 ` Jason Low
2014-03-13 7:28 ` [tip:core/locking] locking/mutex: Fix debug checks tip-bot for Peter Zijlstra
2014-01-28 19:13 ` [RFC][PATCH v2 4/5] mutex: Disable preemtion between modifying lock->owner and locking/unlocking mutex Jason Low
2014-01-28 20:54 ` Peter Zijlstra
2014-01-28 22:17 ` Jason Low
2014-01-28 19:13 ` [RFC][PATCH v2 5/5] mutex: Give spinners a chance to spin_on_owner if need_resched() triggered while queued Jason Low
2014-01-28 21:07 ` Peter Zijlstra
2014-01-28 22:51 ` Jason Low
2014-01-29 11:51 ` Peter Zijlstra
2014-01-31 3:29 ` Jason Low
2014-01-31 14:09 ` Peter Zijlstra
2014-01-31 20:01 ` Jason Low
2014-01-31 20:08 ` Peter Zijlstra
2014-02-02 21:01 ` Jason Low
2014-02-02 21:12 ` Peter Zijlstra
2014-02-03 18:39 ` Jason Low
2014-02-03 19:25 ` Peter Zijlstra
2014-02-03 20:55 ` Jason Low
2014-02-03 21:06 ` Peter Zijlstra
2014-02-03 21:56 ` Jason Low
2014-02-04 7:13 ` Jason Low
2014-02-02 22:02 ` Paul E. McKenney
2014-02-02 20:02 ` Peter Zijlstra
2014-02-05 21:44 ` Waiman Long
2014-02-06 14:04 ` Peter Zijlstra
2014-02-06 18:45 ` Waiman Long
2014-02-06 20:10 ` Norton, Scott J
2014-02-10 17:01 ` Peter Zijlstra
2014-02-06 17:44 ` Jason Low
2014-02-06 18:37 ` Waiman Long
2014-01-28 21:08 ` [PATCH v2 0/5] mutex: Mutex scalability patches Davidlohr Bueso
2014-01-28 23:11 ` Jason Low
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