Messages in this thread | | | Date | Tue, 14 Jun 2016 13:08:13 +0100 | From | Juri Lelli <> | Subject | Re: [RFC][PATCH 5/8] rtmutex: Clean up |
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Hi,
On 07/06/16 21:56, Peter Zijlstra wrote: > Previous patches changed the meaning of the return value of > rt_mutex_slowunlock(); update comments and code to reflect this. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > kernel/futex.c | 12 ++++++------ > kernel/locking/rtmutex.c | 20 +++++++++----------- > kernel/locking/rtmutex_common.h | 2 +- > 3 files changed, 16 insertions(+), 18 deletions(-) > > --- a/kernel/futex.c > +++ b/kernel/futex.c > @@ -1261,7 +1261,7 @@ static int wake_futex_pi(u32 __user *uad > struct futex_pi_state *pi_state = this->pi_state; > u32 uninitialized_var(curval), newval; > WAKE_Q(wake_q); > - bool deboost; > + bool postunlock; > int ret = 0; > > if (!pi_state) > @@ -1327,17 +1327,17 @@ static int wake_futex_pi(u32 __user *uad > > raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); > > - deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q); > + postunlock = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q); > > /* > * First unlock HB so the waiter does not spin on it once he got woken > - * up. Second wake up the waiter before the priority is adjusted. If we > - * deboost first (and lose our higher priority), then the task might get > - * scheduled away before the wake up can take place. > + * up. Then wakeup the waiter by calling rt_mutex_postunlock(). Priority > + * is already adjusted and preemption is disabled to avoid inversion. > */ > spin_unlock(&hb->lock); > > - rt_mutex_postunlock(&wake_q, deboost); > + if (postunlock) > + rt_mutex_postunlock(&wake_q);
I'm most probably missing something, but don't we still need to call wake_up_q() even when postunlock is false? IIUC, we were always doing that, rt_mutex_postunlock(), before this change (only calling preempt_enable() was conditional).
Best,
- Juri
> > return 0; > } > --- a/kernel/locking/rtmutex.c > +++ b/kernel/locking/rtmutex.c > @@ -1254,7 +1254,8 @@ static inline int rt_mutex_slowtrylock(s > > /* > * Slow path to release a rt-mutex. > - * Return whether the current task needs to undo a potential priority boosting. > + * > + * Return whether the current task needs to call rt_mutex_postunlock(). > */ > static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock, > struct wake_q_head *wake_q) > @@ -1327,7 +1328,7 @@ static bool __sched rt_mutex_slowunlock( > > raw_spin_unlock_irqrestore(&lock->wait_lock, flags); > > - /* check PI boosting */ > + /* call rt_mutex_postunlock() */ > return true; > } > > @@ -1378,15 +1379,14 @@ rt_mutex_fasttrylock(struct rt_mutex *lo > } > > /* > - * Undo pi boosting (if necessary) and wake top waiter. > + * Performs the wakeup of the the top-waiter and re-enables preemption. > */ > -void rt_mutex_postunlock(struct wake_q_head *wake_q, bool deboost) > +void rt_mutex_postunlock(struct wake_q_head *wake_q) > { > wake_up_q(wake_q); > > /* Pairs with preempt_disable() in rt_mutex_slowunlock() */ > - if (deboost) > - preempt_enable(); > + preempt_enable(); > } > > /** > @@ -1489,9 +1489,8 @@ void __sched rt_mutex_unlock(struct rt_m > rt_mutex_deadlock_account_unlock(current); > > } else { > - bool deboost = rt_mutex_slowunlock(lock, &wake_q); > - > - rt_mutex_postunlock(&wake_q, deboost); > + if (rt_mutex_slowunlock(lock, &wake_q)) > + rt_mutex_postunlock(&wake_q); > } > } > EXPORT_SYMBOL_GPL(rt_mutex_unlock); > @@ -1500,8 +1499,7 @@ EXPORT_SYMBOL_GPL(rt_mutex_unlock); > * rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock > * @lock: the rt_mutex to be unlocked > * > - * Returns: true/false indicating whether priority adjustment is > - * required or not. > + * Returns: true/false indicating whether we should call rt_mutex_postunlock(). > */ > bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock, > struct wake_q_head *wqh) > --- a/kernel/locking/rtmutex_common.h > +++ b/kernel/locking/rtmutex_common.h > @@ -111,7 +111,7 @@ extern int rt_mutex_finish_proxy_lock(st > extern int rt_mutex_timed_futex_lock(struct rt_mutex *l, struct hrtimer_sleeper *to); > extern bool rt_mutex_futex_unlock(struct rt_mutex *lock, > struct wake_q_head *wqh); > -extern void rt_mutex_postunlock(struct wake_q_head *wake_q, bool deboost); > +extern void rt_mutex_postunlock(struct wake_q_head *wake_q); > extern void rt_mutex_adjust_prio(struct task_struct *task); > > #ifdef CONFIG_DEBUG_RT_MUTEXES > >
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