On Thu, 11 May 2017, Wanpeng Li wrote:
> 2017-05-09 23:11 GMT+08:00 Thomas Gleixner <[email protected]>:
> > 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 <[email protected]>
> > Reported-by: Engleder Gerhard <[email protected]>
> > ---
> > 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
