linux-kernel - Re: [PATCH-tip v3 06/11] locking/rwsem: Enhance DEBUG_RWSEMS_WARN

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Message-ID: <20190403130934.GH4038@hirez.programming.kicks-ass.net>
Date:   Wed, 3 Apr 2019 15:09:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH-tip v3 06/11] locking/rwsem: Enhance
 DEBUG_RWSEMS_WARN_ON() macro

On Thu, Feb 28, 2019 at 02:09:36PM -0500, Waiman Long wrote:
> diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
> index 1d8f722..c8fd3f1 100644
> --- a/kernel/locking/rwsem.h
> +++ b/kernel/locking/rwsem.h
> @@ -27,9 +27,13 @@
>  #define RWSEM_ANONYMOUSLY_OWNED	(1UL << 1)
>  
>  #ifdef CONFIG_DEBUG_RWSEMS
> -# define DEBUG_RWSEMS_WARN_ON(c)	DEBUG_LOCKS_WARN_ON(c)
> +# define DEBUG_RWSEMS_WARN_ON(c, sem)				\
> +	WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
> +		#c, atomic_long_read(&(sem)->count),		\
> +		(long)((sem)->owner), (long)current,		\
> +		list_empty(&(sem)->wait_list) ? "" : "not ")

This changes DEBUG_LOCKS_WARN_ON() to WARN_ONCE(), the difference being
that you now fail to kill lockdep on a rwsem error, which seems
unfortunate.

>  #else
> -# define DEBUG_RWSEMS_WARN_ON(c)
> +# define DEBUG_RWSEMS_WARN_ON(c, sem)
>  #endif