Re: [locking/ww_mutex] 2a0c112828 WARNING: CPU: 0 PID: 18 at kernel/locking/mutex.c:305 __ww_mutex_wakeup_for_backoff

From: Fengguang Wu
Date: Wed Mar 01 2017 - 10:55:28 EST

On Wed, Mar 01, 2017 at 04:51:36PM +0100, Peter Zijlstra wrote:
On Wed, Mar 01, 2017 at 11:40:43PM +0800, Fengguang Wu wrote:
Thanks for the patch! I applied the patch on top of "locking/ww_mutex:
Add kselftests for ww_mutex stress", and find no "bad unlock balance
detected" but this warning. Attached is the new dmesg which is a bit
large due to lots of repeated errors.

[ 9.105427] Freeing initrd memory: 24852K
[ 9.121306] The force parameter has not been set to 1. The Iris poweroff handler will not be installed.
[ 9.141216] NatSemi SCx200 Driver
[ 9.724519] ------------[ cut here ]------------
[ 9.726795] WARNING: CPU: 0 PID: 22 at kernel/locking/mutex.c:305 __ww_mutex_wakeup_for_backoff+0x31/0x7a
[ 9.738281] CPU: 0 PID: 22 Comm: kworker/u2:1 Not tainted 4.10.0-rc3-00156-g7d81c50 #1
[ 9.741977] Workqueue: test-ww_mutex test_cycle_work
[ 9.745524] Call Trace:
[ 9.747610] dump_stack+0x16/0x18
[ 9.754619] __warn+0xa0/0xb7
[ 9.757553] ? __ww_mutex_wakeup_for_backoff+0x31/0x7a
[ 9.760881] warn_slowpath_null+0x11/0x16
[ 9.765222] __ww_mutex_wakeup_for_backoff+0x31/0x7a
[ 9.768028] __ww_mutex_lock+0x2f3/0xb63
[ 9.770979] ? wake_up_q+0x25/0x40
[ 9.773044] ? __might_sleep+0x6c/0x73
[ 9.774890] ww_mutex_lock+0x34/0x3b
[ 9.776001] ? test_cycle_work+0xf7/0x170
[ 9.777751] test_cycle_work+0xf7/0x170
[ 9.779036] process_one_work+0x1c0/0x33a
[ 9.780664] ? process_one_work+0x168/0x33a
[ 9.788924] worker_thread+0x22f/0x315
[ 9.791016] kthread+0xed/0xf2
[ 9.793255] ? process_scheduled_works+0x24/0x24
[ 9.795475] ? __kthread_create_on_node+0x11f/0x11f
[ 9.798741] ? __kthread_create_on_node+0x11f/0x11f
[ 9.802371] ret_from_fork+0x19/0x30
[ 9.804430] ---[ end trace 9036bbb174aed804 ]---

Do you have the below patch in?

Nope. I'll re-test with it added.

Regards,
Fengguang

---
commit b9c16a0e1f733c97e48798b2a9362c485bb3b731
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Tue Jan 17 16:06:09 2017 +0100

locking/mutex: Fix lockdep_assert_held() fail

In commit:

659cf9f5824a ("locking/ww_mutex: Optimize ww-mutexes by waking at most one waiter for backoff when acquiring the lock")

I replaced a comment with a lockdep_assert_held(). However it turns out
we hide that lock from lockdep for hysterical raisins, which results
in the assertion always firing.

Remove the old debug code as lockdep will easily spot the abuse it was
meant to catch, which will make the lock visible to lockdep and make
the assertion work as intended.

Reported-by: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Nicolai Haehnle <Nicolai.Haehnle@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 659cf9f5824a ("locking/ww_mutex: Optimize ww-mutexes by waking at most one waiter for backoff when acquiring the lock")
Link: http://lkml.kernel.org/r/20170117150609.GB32474@worktop
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>

diff --git a/kernel/locking/mutex-debug.h b/kernel/locking/mutex-debug.h
index a459faa48987..4174417d5309 100644
--- a/kernel/locking/mutex-debug.h
+++ b/kernel/locking/mutex-debug.h
@@ -26,20 +26,3 @@ extern void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
extern void debug_mutex_unlock(struct mutex *lock);
extern void debug_mutex_init(struct mutex *lock, const char *name,
struct lock_class_key *key);
-
-#define spin_lock_mutex(lock, flags) \
- do { \
- struct mutex *l = container_of(lock, struct mutex, wait_lock); \
- \
- DEBUG_LOCKS_WARN_ON(in_interrupt()); \
- local_irq_save(flags); \
- arch_spin_lock(&(lock)->rlock.raw_lock);\
- DEBUG_LOCKS_WARN_ON(l->magic != l); \
- } while (0)
-
-#define spin_unlock_mutex(lock, flags) \
- do { \
- arch_spin_unlock(&(lock)->rlock.raw_lock); \
- local_irq_restore(flags); \
- preempt_check_resched(); \
- } while (0)
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 935116723a3d..705e06fe5e6c 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -325,8 +325,6 @@ __ww_mutex_wakeup_for_backoff(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
static __always_inline void
ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
- unsigned long flags;
-
ww_mutex_lock_acquired(lock, ctx);

lock->ctx = ctx;
@@ -350,9 +348,9 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
* Uh oh, we raced in fastpath, wake up everyone in this case,
* so they can see the new lock->ctx.
*/
- spin_lock_mutex(&lock->base.wait_lock, flags);
+ spin_lock(&lock->base.wait_lock);
__ww_mutex_wakeup_for_backoff(&lock->base, ctx);
- spin_unlock_mutex(&lock->base.wait_lock, flags);
+ spin_unlock(&lock->base.wait_lock);
}

/*
@@ -740,7 +738,6 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
{
struct mutex_waiter waiter;
- unsigned long flags;
bool first = false;
struct ww_mutex *ww;
int ret;
@@ -766,7 +763,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
return 0;
}

- spin_lock_mutex(&lock->wait_lock, flags);
+ spin_lock(&lock->wait_lock);
/*
* After waiting to acquire the wait_lock, try again.
*/
@@ -830,7 +827,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
goto err;
}

- spin_unlock_mutex(&lock->wait_lock, flags);
+ spin_unlock(&lock->wait_lock);
schedule_preempt_disabled();

/*
@@ -853,9 +850,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
(first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
break;

- spin_lock_mutex(&lock->wait_lock, flags);
+ spin_lock(&lock->wait_lock);
}
- spin_lock_mutex(&lock->wait_lock, flags);
+ spin_lock(&lock->wait_lock);
acquired:
__set_current_state(TASK_RUNNING);

@@ -872,7 +869,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
if (use_ww_ctx && ww_ctx)
ww_mutex_set_context_slowpath(ww, ww_ctx);

- spin_unlock_mutex(&lock->wait_lock, flags);
+ spin_unlock(&lock->wait_lock);
preempt_enable();
return 0;

@@ -880,7 +877,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
__set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, current);
err_early_backoff:
- spin_unlock_mutex(&lock->wait_lock, flags);
+ spin_unlock(&lock->wait_lock);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, 1, ip);
preempt_enable();
@@ -999,8 +996,8 @@ EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
{
struct task_struct *next = NULL;
- unsigned long owner, flags;
DEFINE_WAKE_Q(wake_q);
+ unsigned long owner;

mutex_release(&lock->dep_map, 1, ip);

@@ -1035,7 +1032,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
owner = old;
}

- spin_lock_mutex(&lock->wait_lock, flags);
+ spin_lock(&lock->wait_lock);
debug_mutex_unlock(lock);
if (!list_empty(&lock->wait_list)) {
/* get the first entry from the wait-list: */
@@ -1052,7 +1049,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
if (owner & MUTEX_FLAG_HANDOFF)
__mutex_handoff(lock, next);

- spin_unlock_mutex(&lock->wait_lock, flags);
+ spin_unlock(&lock->wait_lock);

wake_up_q(&wake_q);
}
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 4410a4af42a3..6ebc1902f779 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -9,10 +9,6 @@
* !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:
*/

-#define spin_lock_mutex(lock, flags) \
- do { spin_lock(lock); (void)(flags); } while (0)
-#define spin_unlock_mutex(lock, flags) \
- do { spin_unlock(lock); (void)(flags); } while (0)
#define mutex_remove_waiter(lock, waiter, task) \
__list_del((waiter)->list.prev, (waiter)->list.next)