* [PATCH RT] futex/rtmutex: Cure RT double blocking issue
@ 2017-05-09 15:11 Thomas Gleixner
2017-05-09 15:49 ` Steven Rostedt
2017-05-11 2:25 ` Wanpeng Li
0 siblings, 2 replies; 7+ messages in thread
From: Thomas Gleixner @ 2017-05-09 15:11 UTC (permalink / raw)
To: LKML
Cc: Sebastian Sewior, Peter Zijlstra, Steven Rostedt, linux-rt-users,
Engleder Gerhard
RT has a problem when the wait on a futex/rtmutex got interrupted by a
timeout or a signal. task->pi_blocked_on is still set when returning from
rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
after this.
If the hash bucket lock is contended then the
BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
task_blocks_on_rt_mutex() will trigger.
This can be avoided by clearing task->pi_blocked_on in the return path of
rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
of the rtmutex. That's correct because the task is not longer blocked on
it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Engleder Gerhard <eg@keba.com>
---
kernel/locking/rtmutex.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -2380,6 +2380,7 @@ int rt_mutex_wait_proxy_lock(struct rt_m
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter)
{
+ struct task_struct *tsk = current;
int ret;
raw_spin_lock_irq(&lock->wait_lock);
@@ -2389,6 +2390,22 @@ int rt_mutex_wait_proxy_lock(struct rt_m
/* sleep on the mutex */
ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
+ /*
+ * RT has a problem here when the wait got interrupted by a timeout
+ * or a signal. task->pi_blocked_on is still set. The task must
+ * acquire the hash bucket lock when returning from this function.
+ *
+ * If the hash bucket lock is contended then the
+ * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
+ * task_blocks_on_rt_mutex() will trigger. This can be avoided by
+ * clearing task->pi_blocked_on which removes the task from the
+ * boosting chain of the rtmutex. That's correct because the task
+ * is not longer blocked on it.
+ */
+ raw_spin_lock(&tsk->pi_lock);
+ tsk->pi_blocked_on = NULL;
+ raw_spin_unlock(&tsk->pi_lock);
+
raw_spin_unlock_irq(&lock->wait_lock);
return ret;
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH RT] futex/rtmutex: Cure RT double blocking issue
2017-05-09 15:11 [PATCH RT] futex/rtmutex: Cure RT double blocking issue Thomas Gleixner
@ 2017-05-09 15:49 ` Steven Rostedt
2017-05-11 2:25 ` Wanpeng Li
1 sibling, 0 replies; 7+ messages in thread
From: Steven Rostedt @ 2017-05-09 15:49 UTC (permalink / raw)
To: Thomas Gleixner
Cc: LKML, Sebastian Sewior, Peter Zijlstra, linux-rt-users, Engleder Gerhard
On Tue, 9 May 2017 17:11:10 +0200 (CEST)
Thomas Gleixner <tglx@linutronix.de> wrote:
> RT has a problem when the wait on a futex/rtmutex got interrupted by a
> timeout or a signal. task->pi_blocked_on is still set when returning from
> rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
> after this.
>
> If the hash bucket lock is contended then the
> BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
> task_blocks_on_rt_mutex() will trigger.
>
> This can be avoided by clearing task->pi_blocked_on in the return path of
> rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
> of the rtmutex. That's correct because the task is not longer blocked on
s/not/no/
> it.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reported-by: Engleder Gerhard <eg@keba.com>
> ---
> kernel/locking/rtmutex.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -2380,6 +2380,7 @@ int rt_mutex_wait_proxy_lock(struct rt_m
> struct hrtimer_sleeper *to,
> struct rt_mutex_waiter *waiter)
> {
> + struct task_struct *tsk = current;
> int ret;
>
> raw_spin_lock_irq(&lock->wait_lock);
> @@ -2389,6 +2390,22 @@ int rt_mutex_wait_proxy_lock(struct rt_m
> /* sleep on the mutex */
> ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
>
> + /*
> + * RT has a problem here when the wait got interrupted by a timeout
> + * or a signal. task->pi_blocked_on is still set. The task must
> + * acquire the hash bucket lock when returning from this function.
> + *
> + * If the hash bucket lock is contended then the
> + * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
> + * task_blocks_on_rt_mutex() will trigger. This can be avoided by
> + * clearing task->pi_blocked_on which removes the task from the
> + * boosting chain of the rtmutex. That's correct because the task
> + * is not longer blocked on it.
s/not/no/
I looked at the users of pi_blocked_on, and this appears to be fine.
I don't see it used by remove_waiter() where it clears it at the start.
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
> + */
> + raw_spin_lock(&tsk->pi_lock);
> + tsk->pi_blocked_on = NULL;
> + raw_spin_unlock(&tsk->pi_lock);
> +
> raw_spin_unlock_irq(&lock->wait_lock);
>
> return ret;
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH RT] futex/rtmutex: Cure RT double blocking issue
2017-05-09 15:11 [PATCH RT] futex/rtmutex: Cure RT double blocking issue Thomas Gleixner
2017-05-09 15:49 ` Steven Rostedt
@ 2017-05-11 2:25 ` Wanpeng Li
2017-05-11 7:31 ` Thomas Gleixner
1 sibling, 1 reply; 7+ messages in thread
From: Wanpeng Li @ 2017-05-11 2:25 UTC (permalink / raw)
To: Thomas Gleixner
Cc: LKML, Sebastian Sewior, Peter Zijlstra, Steven Rostedt,
linux-rt-users, Engleder Gerhard
2017-05-09 23:11 GMT+08:00 Thomas Gleixner <tglx@linutronix.de>:
> RT has a problem when the wait on a futex/rtmutex got interrupted by a
> timeout or a signal. task->pi_blocked_on is still set when returning from
> rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
> after this.
>
> If the hash bucket lock is contended then the
> BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
> task_blocks_on_rt_mutex() will trigger.
>
> This can be avoided by clearing task->pi_blocked_on in the return path of
> rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
> of the rtmutex. That's correct because the task is not longer blocked on
> it.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reported-by: Engleder Gerhard <eg@keba.com>
> ---
> kernel/locking/rtmutex.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -2380,6 +2380,7 @@ int rt_mutex_wait_proxy_lock(struct rt_m
> struct hrtimer_sleeper *to,
> struct rt_mutex_waiter *waiter)
> {
> + struct task_struct *tsk = current;
> int ret;
>
> raw_spin_lock_irq(&lock->wait_lock);
> @@ -2389,6 +2390,22 @@ int rt_mutex_wait_proxy_lock(struct rt_m
> /* sleep on the mutex */
> ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
Why not check the ret value to avoid lock/unlock tsk->pi_lock when
acquires the rt_mutex successfully?
Regards,
Wanpeng Li
>
> + /*
> + * RT has a problem here when the wait got interrupted by a timeout
> + * or a signal. task->pi_blocked_on is still set. The task must
> + * acquire the hash bucket lock when returning from this function.
> + *
> + * If the hash bucket lock is contended then the
> + * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
> + * task_blocks_on_rt_mutex() will trigger. This can be avoided by
> + * clearing task->pi_blocked_on which removes the task from the
> + * boosting chain of the rtmutex. That's correct because the task
> + * is not longer blocked on it.
> + */
> + raw_spin_lock(&tsk->pi_lock);
> + tsk->pi_blocked_on = NULL;
> + raw_spin_unlock(&tsk->pi_lock);
> +
> raw_spin_unlock_irq(&lock->wait_lock);
>
> return ret;
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH RT] futex/rtmutex: Cure RT double blocking issue
2017-05-11 2:25 ` Wanpeng Li
@ 2017-05-11 7:31 ` Thomas Gleixner
2017-05-11 15:20 ` [PATCH RT v2] " Sebastian Sewior
0 siblings, 1 reply; 7+ messages in thread
From: Thomas Gleixner @ 2017-05-11 7:31 UTC (permalink / raw)
To: Wanpeng Li
Cc: LKML, Sebastian Sewior, Peter Zijlstra, Steven Rostedt,
linux-rt-users, Engleder Gerhard
On Thu, 11 May 2017, Wanpeng Li wrote:
> 2017-05-09 23:11 GMT+08:00 Thomas Gleixner <tglx@linutronix.de>:
> > RT has a problem when the wait on a futex/rtmutex got interrupted by a
> > timeout or a signal. task->pi_blocked_on is still set when returning from
> > rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
> > after this.
> >
> > If the hash bucket lock is contended then the
> > BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
> > task_blocks_on_rt_mutex() will trigger.
> >
> > This can be avoided by clearing task->pi_blocked_on in the return path of
> > rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
> > of the rtmutex. That's correct because the task is not longer blocked on
> > it.
> >
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > Reported-by: Engleder Gerhard <eg@keba.com>
> > ---
> > kernel/locking/rtmutex.c | 17 +++++++++++++++++
> > 1 file changed, 17 insertions(+)
> >
> > --- a/kernel/locking/rtmutex.c
> > +++ b/kernel/locking/rtmutex.c
> > @@ -2380,6 +2380,7 @@ int rt_mutex_wait_proxy_lock(struct rt_m
> > struct hrtimer_sleeper *to,
> > struct rt_mutex_waiter *waiter)
> > {
> > + struct task_struct *tsk = current;
> > int ret;
> >
> > raw_spin_lock_irq(&lock->wait_lock);
> > @@ -2389,6 +2390,22 @@ int rt_mutex_wait_proxy_lock(struct rt_m
> > /* sleep on the mutex */
> > ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
>
> Why not check the ret value to avoid lock/unlock tsk->pi_lock when
> acquires the rt_mutex successfully?
Make sense.
Thanks,
tglx
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH RT v2] futex/rtmutex: Cure RT double blocking issue
2017-05-11 7:31 ` Thomas Gleixner
@ 2017-05-11 15:20 ` Sebastian Sewior
2017-05-11 15:54 ` Steven Rostedt
0 siblings, 1 reply; 7+ messages in thread
From: Sebastian Sewior @ 2017-05-11 15:20 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Wanpeng Li, LKML, Peter Zijlstra, Steven Rostedt, linux-rt-users,
Engleder Gerhard
RT has a problem when the wait on a futex/rtmutex got interrupted by a
timeout or a signal. task->pi_blocked_on is still set when returning from
rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
after this.
If the hash bucket lock is contended then the
BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
task_blocks_on_rt_mutex() will trigger.
This can be avoided by clearing task->pi_blocked_on in the return path of
rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
of the rtmutex. That's correct because the task is not longer blocked on
it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Engleder Gerhard <eg@keba.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
v1…v2: reset ->pi_blocked_on only in the error case.
kernel/locking/rtmutex.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 314fc65a35b1..4675f1197f33 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -2400,6 +2400,7 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter)
{
+ struct task_struct *tsk = current;
int ret;
raw_spin_lock_irq(&lock->wait_lock);
@@ -2409,6 +2410,24 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
/* sleep on the mutex */
ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
+ /*
+ * RT has a problem here when the wait got interrupted by a timeout
+ * or a signal. task->pi_blocked_on is still set. The task must
+ * acquire the hash bucket lock when returning from this function.
+ *
+ * If the hash bucket lock is contended then the
+ * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
+ * task_blocks_on_rt_mutex() will trigger. This can be avoided by
+ * clearing task->pi_blocked_on which removes the task from the
+ * boosting chain of the rtmutex. That's correct because the task
+ * is not longer blocked on it.
+ */
+ if (ret) {
+ raw_spin_lock(&tsk->pi_lock);
+ tsk->pi_blocked_on = NULL;
+ raw_spin_unlock(&tsk->pi_lock);
+ }
+
raw_spin_unlock_irq(&lock->wait_lock);
return ret;
--
2.11.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH RT v2] futex/rtmutex: Cure RT double blocking issue
2017-05-11 15:20 ` [PATCH RT v2] " Sebastian Sewior
@ 2017-05-11 15:54 ` Steven Rostedt
2017-05-11 16:05 ` Sebastian Sewior
0 siblings, 1 reply; 7+ messages in thread
From: Steven Rostedt @ 2017-05-11 15:54 UTC (permalink / raw)
To: Sebastian Sewior
Cc: Thomas Gleixner, Wanpeng Li, LKML, Peter Zijlstra,
linux-rt-users, Engleder Gerhard
On Thu, 11 May 2017 17:20:54 +0200
Sebastian Sewior <bigeasy@linutronix.de> wrote:
This is the same patch that Thomas wrote, right? Shouldn't this start
with:
From: Thomas Gleixner <tglx@linutronix.de>
?
-- Steve
> RT has a problem when the wait on a futex/rtmutex got interrupted by a
> timeout or a signal. task->pi_blocked_on is still set when returning from
> rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
> after this.
>
> If the hash bucket lock is contended then the
> BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
> task_blocks_on_rt_mutex() will trigger.
>
> This can be avoided by clearing task->pi_blocked_on in the return path of
> rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
> of the rtmutex. That's correct because the task is not longer blocked on
> it.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reported-by: Engleder Gerhard <eg@keba.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> v1…v2: reset ->pi_blocked_on only in the error case.
>
> kernel/locking/rtmutex.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 314fc65a35b1..4675f1197f33 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -2400,6 +2400,7 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
> struct hrtimer_sleeper *to,
> struct rt_mutex_waiter *waiter)
> {
> + struct task_struct *tsk = current;
> int ret;
>
> raw_spin_lock_irq(&lock->wait_lock);
> @@ -2409,6 +2410,24 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
> /* sleep on the mutex */
> ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
>
> + /*
> + * RT has a problem here when the wait got interrupted by a timeout
> + * or a signal. task->pi_blocked_on is still set. The task must
> + * acquire the hash bucket lock when returning from this function.
> + *
> + * If the hash bucket lock is contended then the
> + * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
> + * task_blocks_on_rt_mutex() will trigger. This can be avoided by
> + * clearing task->pi_blocked_on which removes the task from the
> + * boosting chain of the rtmutex. That's correct because the task
> + * is not longer blocked on it.
> + */
> + if (ret) {
> + raw_spin_lock(&tsk->pi_lock);
> + tsk->pi_blocked_on = NULL;
> + raw_spin_unlock(&tsk->pi_lock);
> + }
> +
> raw_spin_unlock_irq(&lock->wait_lock);
>
> return ret;
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH RT v2] futex/rtmutex: Cure RT double blocking issue
2017-05-11 15:54 ` Steven Rostedt
@ 2017-05-11 16:05 ` Sebastian Sewior
0 siblings, 0 replies; 7+ messages in thread
From: Sebastian Sewior @ 2017-05-11 16:05 UTC (permalink / raw)
To: Steven Rostedt
Cc: Thomas Gleixner, Wanpeng Li, LKML, Peter Zijlstra,
linux-rt-users, Engleder Gerhard
On 2017-05-11 11:54:47 [-0400], Steven Rostedt wrote:
> This is the same patch that Thomas wrote, right? Shouldn't this start
> with:
>
> From: Thomas Gleixner <tglx@linutronix.de>
>
> ?
correct. It made its way properly into the patch queue, I just managed
to get it wrong while sending it to the list…
> -- Steve
Sebastian
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2017-05-11 16:05 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2017-05-09 15:11 [PATCH RT] futex/rtmutex: Cure RT double blocking issue Thomas Gleixner
2017-05-09 15:49 ` Steven Rostedt
2017-05-11 2:25 ` Wanpeng Li
2017-05-11 7:31 ` Thomas Gleixner
2017-05-11 15:20 ` [PATCH RT v2] " Sebastian Sewior
2017-05-11 15:54 ` Steven Rostedt
2017-05-11 16:05 ` Sebastian Sewior
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