linux-kernel - Re: slab error in verify_redzone

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Date:	Mon, 2 Feb 2009 15:18:52 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrew Vasquez <andrew.vasquez@...gic.com>
Cc:	matthew@....cx, gregkh@...e.de, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, seokmann.ju@...gic.com
Subject: Re: slab error in verify_redzone_free() badness...

On Thu, 29 Jan 2009 14:55:32 -0800
Andrew Vasquez <andrew.vasquez@...gic.com> wrote:

> Matthew,
> 
> During some NPIV regression tests with .29-rc3, we are seeing some
> slab-corruption during vport tear-down:
> 
> 	# create vport off fc-host1
> 	$ echo "2001567890abcdab:2001ef12345678ab" > /sys/class/fc_host/host1/vport_create
> 	# delete vport
> 	$ echo "2001567890abcdab:2001ef12345678ab" > /sys/class/fc_host/host1/vport_delete
> 
> Here's the backtrace:
> 
> 	[  263.337035] slab error in verify_redzone_free(): cache `size-2048': memory outside object was overwritten
> 	[  263.340213] Pid: 7623, comm: bash Tainted: G   M       2.6.28 #32
> 	[  263.340213] Call Trace:
> 	[  263.340213]  [<ffffffff8027afd7>] __slab_error+0x1c/0x25
> 	[  263.340213]  [<ffffffff8027b43b>] cache_free_debugcheck+0x165/0x210
> 	[  263.340213]  [<ffffffff8027b672>] kfree+0x6b/0xc3
> 	[  263.340213]  [<ffffffff803947bb>] device_release+0x1a/0x6a
> 	[  263.340213]  [<ffffffff8032db9c>] kobject_release+0x33/0x63
> 	[  263.340213]  [<ffffffff8032db69>] kobject_release+0x0/0x63
> 	[  263.340213]  [<ffffffff8032e98e>] kref_put+0x32/0x6c
> 	[  263.340213]  [<ffffffffa002b73b>] qla24xx_vport_delete+0xc7/0x14f [qla2xxx]
> 	[  263.340213]  [<ffffffffa000061c>] fc_vport_terminate+0x81/0x1bb [scsi_transport_fc]
> 	[  263.340213]  [<ffffffffa0002a67>] store_fc_host_vport_delete+0x111/0x121 [scsi_transport_fc]
> 	[  263.340213]  [<ffffffff802bebea>] sysfs_write_file+0xb3/0x114
> 	[  263.340213]  [<ffffffff802803a3>] vfs_write+0xac/0x147
> 	[  263.340213]  [<ffffffff80280921>] sys_write+0x45/0x73
> 	[  263.340213]  [<ffffffff8020b45b>] system_call_fastpath+0x16/0x1b
> 	[  263.340213] ffff88007ddaad98: redzone 1:0xd84156c5635688c0, redzone 2:0x0.
> 
> We've bisected the problem down to:
> 
> 	commit 210272a28465a7a31bcd580d2f9529f924965aa5
> 	Author: Matthew Wilcox <matthew@....cx>
> 	Date:   Thu Oct 16 14:57:54 2008 -0600
> 
> 	    driver core: Remove completion from struct klist_node
> 
> 	    Removing the completion from klist_node reduces its size from 64 bytes
> 	    to 28 on x86-64.  To maintain the semantics of klist_remove(), we add
> 	    a single list of klist nodes which are pending deletion and scan them.
> 
> 	    Signed-off-by: Matthew Wilcox <willy@...ux.intel.com>
> 	    Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
> 
> At first glance the changes look fairly straight-forward...  Reverting
> the problem commit (currently off .29-rc3) appears to clean up the
> slab-badness.
> 
> Thoughts?

I'd be suspecting a bug in the caller.

Try setting CONFIG_DEBUG_PAGEALLOC, and use slab.c (not slub).  slab
will perform page unmapping for those 2k-sized slabs.  I don't know
whether slub does that.

All being well, you'll get a nice oops at the site of the improper
reference.

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