linux-kernel - Re: [PATCH] futex: move debug_rt_mutex_free

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Message-ID: <20170308112059.64e06683@gandalf.local.home>
Date:   Wed, 8 Mar 2017 11:20:59 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
        mingo@...nel.org, juri.lelli@....com, xlpang@...hat.com,
        linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
        jdesfossez@...icios.com, bristot@...hat.com, dvhart@...radead.org
Subject: Re: [PATCH] futex: move debug_rt_mutex_free_waiter() further down

On Wed, 8 Mar 2017 16:29:02 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> Without this, futex_requeue_pi_signal_restart will trigger
> 
> |kernel BUG at locking/rtmutex_common.h:55!
> |Call Trace:
> | rt_mutex_cleanup_proxy_lock+0x54/0x90
> | futex_wait_requeue_pi.constprop.21+0x387/0x4d0
> | do_futex+0x289/0xbf0
> |RIP: remove_waiter+0x157/0x170 RSP: ffffc90000e0fbe0
> 
> with BUG 2222222222222222 != pointer once this patch is applied.

This sentence makes no sense. It's a no-sensetence ;-)

-- Steve

> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  kernel/futex.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 00ec4a01d3f5..73abfe0da4d0 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -3046,11 +3046,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
>  		WARN_ON(!q.pi_state);
>  		pi_mutex = &q.pi_state->pi_mutex;
>  		ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
> -		debug_rt_mutex_free_waiter(&rt_waiter);
>  
>  		spin_lock(q.lock_ptr);
>  		if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
>  			ret = 0;
> +		debug_rt_mutex_free_waiter(&rt_waiter);
>  
>  		/*
>  		 * Fixup the pi_state owner and possibly acquire the lock if we