linux-kernel - Re: [PATCH v2] mm/slub: introduce SLAB_WARN_ON

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Message-Id: <20190128122954.949c2e6699d6e5ef060a325c@linux-foundation.org>
Date:   Mon, 28 Jan 2019 12:29:54 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     <miles.chen@...iatek.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        "David Rientjes" <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Jonathan Corbet <corbet@....net>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2] mm/slub: introduce SLAB_WARN_ON_ERROR

On Thu, 24 Jan 2019 15:00:23 +0800 <miles.chen@...iatek.com> wrote:

> From: Miles Chen <miles.chen@...iatek.com>
> 
> When debugging slab errors in slub.c, sometimes we have to trigger
> a panic in order to get the coredump file. Add a debug option
> SLAB_WARN_ON_ERROR to toggle WARN_ON() when the option is set.
> 
> Change since v1:
> 1. Add a special debug option SLAB_WARN_ON_ERROR and toggle WARN_ON()
> if it is set.
> 2. SLAB_WARN_ON_ERROR can be set by kernel parameter slub_debug.
> 

Hopefully the slab developers will have an opinion on this.

> --- a/Documentation/vm/slub.rst
> +++ b/Documentation/vm/slub.rst
> @@ -52,6 +52,7 @@ Possible debug options are::
>  	A		Toggle failslab filter mark for the cache
>  	O		Switch debugging off for caches that would have
>  			caused higher minimum slab orders
> +	W		Toggle WARN_ON() on slab errors
>  	-		Switch all debugging off (useful if the kernel is
>  			configured with CONFIG_SLUB_DEBUG_ON)

This documentation is poorly phrased.  The term "toggle" means to
invert the value of a boolean: if it was 1, make it 0 and if it was 0,
make it 1.  But that isn't what these options do.  Something like
"enable/disable" would be better.   So...

--- a/Documentation/vm/slub.rst~mm-slub-introduce-slab_warn_on_error-fix
+++ a/Documentation/vm/slub.rst
@@ -49,10 +49,10 @@ Possible debug options are::
 	P		Poisoning (object and padding)
 	U		User tracking (free and alloc)
 	T		Trace (please only use on single slabs)
-	A		Toggle failslab filter mark for the cache
+	A		Enable/disable failslab filter mark for the cache
 	O		Switch debugging off for caches that would have
 			caused higher minimum slab orders
-	W		Toggle WARN_ON() on slab errors
+	W		Enable/disable WARN_ON() on slab errors
 	-		Switch all debugging off (useful if the kernel is
 			configured with CONFIG_SLUB_DEBUG_ON)
 
_