linux-kernel - Re: [PATCH] [RFC] mutex: w/w mutex slowpath debugging

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Date:	Tue, 30 Apr 2013 15:29:39 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
	peterz@...radead.org, x86@...nel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	robclark@...il.com, daniel@...ll.ch, tglx@...utronix.de,
	mingo@...e.hu, linux-media@...r.kernel.org
Subject: Re: [PATCH] [RFC] mutex: w/w mutex slowpath debugging

On Tue, 2013-04-30 at 20:45 +0200, Daniel Vetter wrote:
> /**
> diff --git a/kernel/mutex.c b/kernel/mutex.c
> index 66807c7..1cc3487 100644
> --- a/kernel/mutex.c
> +++ b/kernel/mutex.c
> @@ -827,6 +827,35 @@ int __sched mutex_trylock(struct mutex *lock)
>  EXPORT_SYMBOL(mutex_trylock);
>  
>  #ifndef CONFIG_DEBUG_LOCK_ALLOC
> +
> +#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
> +static int __sched
> +ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> +{
> +	if (ctx->deadlock_inject_countdown-- == 0) {
> +		tmp = ctx->deadlock_inject_interval;
> +		if (tmp > UINT_MAX/4)
> +			tmp = UINT_MAX;
> +		else
> +			tmp = tmp*2 + tmp + tmp/2;
> +
> +		ctx->deadlock_inject_interval = tmp;
> +		ctx->deadlock_inject_countdown = tmp;
> +
> +		ww_mutex_unlock(lock);
> +
> +		return -EDEADLK;
> +	}
> +
> +	return 0;
> +}
> +#else
> +static int __sched
> +ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> +{
> +	return 0;
> +}

This should be a static inline, and remove the __sched. There's no
reason to make this anything but a nop when disabled.

-- Steve


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