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Date:   Tue, 31 Aug 2021 20:46:36 +0200
From:   Jiri Olsa <jolsa@redhat.com>
To:     =?utf-8?B?5Y+25r6E6ZSL?= <dg573847474@gmail.com>
Cc:     peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
        mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
        namhyung@kernel.org, linux-perf-users@vger.kernel.org,
        linux-kernel@vger.kernel.org, CAI Yuandao <ycaibb@cse.ust.hk>
Subject: Re: Possible deadlock errors in tools/perf/builtin-sched.c
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References: <CAAo+4rXNLdgvAiT2-B8cWtLNPnWoGo9RWMW=8SPchzRgxJ4BhA@mail.gmail.com>
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On Sat, Aug 28, 2021 at 03:57:17PM +0800, 叶澄锋 wrote:
> Dear developers:
> 
> Thank you for your checking.
> 
> It seems there are two deadlock errors on the lock
> *sched->work_done_wait_mutex*and*sched->start_work_mutex.*
> 
> They are triggered due to one thread(A) runs function *run_one_test* locating
> in a loop and unreleasing the two locks in the*wait_for_tasks*function, and
> another thread(B) runs function *thread_func *acquiring the two locks.
> 
> Because the two locks are not properly released in thread A, there will be
> a  deadlock problem if thread B acquires the two locks.

hi,
do you have a way to reproduce this?

thanks,
jirka

> 
> The related codes are below:
> 
> Thread A:
> 
> static void create_tasks(struct perf_sched *sched)
> {
>      ...;
>   err = pthread_mutex_lock(&sched->start_work_mutex);
>     ...;
>  err = pthread_mutex_lock(&sched->work_done_wait_mutex);
>        ...;
> }
> static int perf_sched__replay(struct perf_sched *sched)
> {
>    ...;
> 
>         create_tasks(sched);
>      printf("------------------------------------------------------------\n");
>      for (i = 0; i < sched->replay_repeat; i++)
>           run_one_test(sched);   // multiple reacquisition on the lock
> sched->work_done_wait_mutex and sched->start_work_mutex
> 
>    return 0;
> }
> 
> static void run_one_test(struct perf_sched *sched)
> {
>  ...;
>       wait_for_tasks(sched);
>         ...;
> }
> static void wait_for_tasks(struct perf_sched *sched)
> {
>        ...;
>     pthread_mutex_unlock(&sched->work_done_wait_mutex);
> 
>   ...;
>        ret = pthread_mutex_lock(&sched->work_done_wait_mutex);
>      ...;
>   pthread_mutex_unlock(&sched->start_work_mutex);
> 
>     ...;
> 
>  ret = pthread_mutex_lock(&sched->start_work_mutex);
>    ....;
> }
> 
> Thread B:
> 
> static void *thread_func(void *ctx)
> {
> 
> ...;
> ret = pthread_mutex_lock(&sched->start_work_mutex);
> ...;
> ret = pthread_mutex_unlock(&sched->start_work_mutex);
> 
> ...;
> 
> ret = pthread_mutex_lock(&sched->work_done_wait_mutex);
> ...;
> ret = pthread_mutex_unlock(&sched->work_done_wait_mutex);
> ..;
> 
> }
> 
> 
> Thanks,