linux-kernel - Re: [ipc/sem.c] 6394de3b86: BUG:kernel_NULL_pointer

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Message-ID: <d49d1940-a704-d79e-b44f-79db9f096d5c@colorfullife.com>
Date:   Wed, 23 Oct 2019 20:28:52 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     kernel test robot <rong.a.chen@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Waiman Long <longman@...hat.com>, 1vier1@....de,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jonathan Corbet <corbet@....net>, lkp@...ts.01.org,
        ltp@...ts.linux.it
Subject: Re: [ipc/sem.c] 6394de3b86:
 BUG:kernel_NULL_pointer_dereference,address

Hello,

On 10/21/19 10:35 AM, kernel test robot wrote:
> FYI, we noticed the following commit (built with gcc-7):
>
> commit: 6394de3b868537a90dd9128607192b0e97109f6b ("[PATCH 4/5] ipc/sem.c: Document and update memory barriers")
> url: https://github.com/0day-ci/linux/commits/Manfred-Spraul/wake_q-Cleanup-Documentation-update/20191014-055627

Yes, known issue:

> @@ -2148,9 +2176,11 @@ static long do_semtimedop(int semid, struct 
> sembuf __user *tsops,
>         }
>
>         do {
> -               WRITE_ONCE(queue.status, -EINTR);
> +               /* memory ordering ensured by the lock in sem_lock() */
> +               queue.status = EINTR;
>                 queue.sleeper = current;
>
> +               /* memory ordering is ensured by the lock in sem_lock() */
>                 __set_current_state(TASK_INTERRUPTIBLE);
>                 sem_unlock(sma, locknum);
>                 rcu_read_unlock();
It must be "-EINTR", not "EINTR".

If there is a timeout or a spurious wakeup, then the do_semtimedop() 
returns to user space without unlinking everything properly.

I was able to reproduce the issue: V1 of the series ends up with the 
shown error.

V3 as now merged doesn't fail.

--

     Manfred