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Date: Sat, 21 Mar 2015 19:02:23 +0100
From: Mike Galbraith <umgwanakikbuti@...il.com>
To: Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com>
Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
linux-rt-users <linux-rt-users@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Carsten Emde <C.Emde@...dl.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
John Kacur <jkacur@...hat.com>,
Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH RT 2/4] Revert "timers: do not raise softirq
unconditionally"
On Thu, 2015-03-19 at 10:42 -0600, Thavatchai Makphaibulchoke wrote:
> On 03/19/2015 10:26 AM, Steven Rostedt wrote:
> > On Thu, 19 Mar 2015 09:17:09 +0100
> > Mike Galbraith <umgwanakikbuti@...il.com> wrote:
> >
> >
> >> (aw crap, let's go shopping)... so why is the one in timer.c ok?
> >
> > It's not. Sebastian, you said there were no other cases of rt_mutexes
> > being taken in hard irq context. Looks like timer.c has one.
> >
> > So perhaps the real fix is to get that special case of ownership in
> > hard interrupt context?
> >
> > -- Steve
> >
>
> Steve, I'm still working on the fix we discussed using dummy irq_task.
> I should be able to submit some time next week, if still interested.
>
> Either that, or I think we should remove the function
> spin_do_trylock_in_interrupt() to prevent any possibility of running
> into similar problems in the future.
Why can't we just Let swapper be the owner when in irq with no dummy?
I have "don't raise timer unconditionally" re-applied, the check for a
running callback bits of my nohz_full fixlet, and the below on top of
that, and all _seems_ well.
---
include/linux/spinlock_rt.h | 1
kernel/locking/rtmutex.c | 58 ++++++++++++++++++--------------------------
kernel/time/timer.c | 4 +--
3 files changed, 27 insertions(+), 36 deletions(-)
--- a/include/linux/spinlock_rt.h
+++ b/include/linux/spinlock_rt.h
@@ -22,7 +22,6 @@ extern void __lockfunc rt_spin_lock(spin
extern unsigned long __lockfunc rt_spin_lock_trace_flags(spinlock_t *lock);
extern void __lockfunc rt_spin_lock_nested(spinlock_t *lock, int subclass);
extern void __lockfunc rt_spin_unlock(spinlock_t *lock);
-extern void __lockfunc rt_spin_unlock_after_trylock_in_irq(spinlock_t *lock);
extern void __lockfunc rt_spin_unlock_wait(spinlock_t *lock);
extern int __lockfunc rt_spin_trylock_irqsave(spinlock_t *lock, unsigned long *flags);
extern int __lockfunc rt_spin_trylock_bh(spinlock_t *lock);
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -934,8 +934,10 @@ static inline void rt_spin_lock_fastlock
static inline void rt_spin_lock_fastunlock(struct rt_mutex *lock,
void (*slowfn)(struct rt_mutex *lock))
{
- if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
- rt_mutex_deadlock_account_unlock(current);
+ struct task_struct *owner = rt_mutex_owner(lock);
+
+ if (likely(rt_mutex_cmpxchg(lock, owner, NULL)))
+ rt_mutex_deadlock_account_unlock(owner);
else
slowfn(lock);
}
@@ -1072,11 +1074,16 @@ static void wakeup_next_waiter(struct rt
/*
* Slow path to release a rt_mutex spin_lock style
*/
-static void __sched __rt_spin_lock_slowunlock(struct rt_mutex *lock)
+static void noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
{
+ struct task_struct *owner;
+
+ raw_spin_lock(&lock->wait_lock);
+
debug_rt_mutex_unlock(lock);
- rt_mutex_deadlock_account_unlock(current);
+ owner = rt_mutex_owner(lock);
+ rt_mutex_deadlock_account_unlock(owner);
if (!rt_mutex_has_waiters(lock)) {
lock->owner = NULL;
@@ -1089,24 +1096,8 @@ static void __sched __rt_spin_lock_slowu
raw_spin_unlock(&lock->wait_lock);
/* Undo pi boosting.when necessary */
- rt_mutex_adjust_prio(current);
-}
-
-static void noinline __sched rt_spin_lock_slowunlock(struct rt_mutex *lock)
-{
- raw_spin_lock(&lock->wait_lock);
- __rt_spin_lock_slowunlock(lock);
-}
-
-static void noinline __sched rt_spin_lock_slowunlock_hirq(struct rt_mutex *lock)
-{
- int ret;
-
- do {
- ret = raw_spin_trylock(&lock->wait_lock);
- } while (!ret);
-
- __rt_spin_lock_slowunlock(lock);
+ if (likely(!is_idle_task(owner)))
+ rt_mutex_adjust_prio(owner);
}
void __lockfunc rt_spin_lock(spinlock_t *lock)
@@ -1139,13 +1130,6 @@ void __lockfunc rt_spin_unlock(spinlock_
}
EXPORT_SYMBOL(rt_spin_unlock);
-void __lockfunc rt_spin_unlock_after_trylock_in_irq(spinlock_t *lock)
-{
- /* NOTE: we always pass in '1' for nested, for simplicity */
- spin_release(&lock->dep_map, 1, _RET_IP_);
- rt_spin_lock_fastunlock(&lock->lock, rt_spin_lock_slowunlock_hirq);
-}
-
void __lockfunc __rt_spin_unlock(struct rt_mutex *lock)
{
rt_spin_lock_fastunlock(lock, rt_spin_lock_slowunlock);
@@ -1341,7 +1325,7 @@ static int task_blocks_on_rt_mutex(struc
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
- if (!owner)
+ if (!owner || is_idle_task(owner))
return 0;
raw_spin_lock_irqsave(&owner->pi_lock, flags);
@@ -1746,6 +1730,7 @@ rt_mutex_slowlock(struct rt_mutex *lock,
*/
static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
{
+ struct task_struct *owner;
int ret;
/*
@@ -1763,7 +1748,9 @@ static inline int rt_mutex_slowtrylock(s
if (!raw_spin_trylock(&lock->wait_lock))
return 0;
- ret = try_to_take_rt_mutex(lock, current, NULL);
+ owner = in_irq() ? idle_task(raw_smp_processor_id()) : current;
+
+ ret = try_to_take_rt_mutex(lock, owner, NULL);
/*
* try_to_take_rt_mutex() sets the lock waiters bit
@@ -1886,8 +1873,13 @@ static inline int
rt_mutex_fasttrylock(struct rt_mutex *lock,
int (*slowfn)(struct rt_mutex *lock))
{
- if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
- rt_mutex_deadlock_account_lock(lock, current);
+ struct task_struct *owner = current;
+
+ if (unlikely(in_irq()))
+ owner = idle_task(raw_smp_processor_id());
+
+ if (likely(rt_mutex_cmpxchg(lock, NULL, owner))) {
+ rt_mutex_deadlock_account_lock(lock, owner);
return 1;
}
return slowfn(lock);
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1425,7 +1425,7 @@ unsigned long get_next_timer_interrupt(u
expires = base->next_timer;
}
#ifdef CONFIG_PREEMPT_RT_FULL
- rt_spin_unlock_after_trylock_in_irq(&base->lock);
+ rt_spin_unlock(&base->lock);
#else
spin_unlock(&base->lock);
#endif
@@ -1518,7 +1518,7 @@ void run_local_timers(void)
raise_softirq(TIMER_SOFTIRQ);
out:
#ifdef CONFIG_PREEMPT_RT_FULL
- rt_spin_unlock_after_trylock_in_irq(&base->lock);
+ rt_spin_unlock(&base->lock);
#endif
/* The ; ensures that gcc won't complain in the !RT case */
;
--
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