linux-kernel - Re: [PATCH] mm/slub: Switch slub_debug kernel option to early

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Message-ID: <000001422ed8406b-14bef091-eee0-4e0e-bcdd-a8909c605910-000000@email.amazonses.com>
Date:	Wed, 6 Nov 2013 19:16:33 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Andreas Herrmann <andreas.herrmann@...xeda.com>
cc:	Pekka Enberg <penberg@...nel.org>, Matt Mackall <mpm@...enic.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: Switch slub_debug kernel option to early_param
 to avoid boot panic

On Wed, 6 Nov 2013, Andreas Herrmann wrote:

> When I've used slub_debug kernel option (e.g.
> "slub_debug=,skbuff_fclone_cache" or similar) on a debug session I've
> seen a panic like:

Hmmm.. That looks like its due to some slabs not having names
during early boot. kmem_cache_flags is called with NULL as a parameter.

Are you sure that this fixes the issue? Looks like the
kmem_cache_flag function should fail regardless of how early you set it.

AFAICT the right fix would be:


Subject: slub: Handle NULL parameter in kmem_cache_flags

kmem_cache_flags may be called with NULL parameter during early boot.
Skip the test in that case.

Signed-off-by: Christoph Lameter <cl@...ux.com>

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c	2013-10-15 13:55:44.000000000 -0500
+++ linux/mm/slub.c	2013-11-06 13:09:21.810583134 -0600
@@ -1217,7 +1217,7 @@ static unsigned long kmem_cache_flags(un
 	/*
 	 * Enable debugging if selected on the kernel commandline.
 	 */
-	if (slub_debug && (!slub_debug_slabs ||
+	if (slub_debug && name && (!slub_debug_slabs ||
 		!strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs))))
 		flags |= slub_debug;



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