linux-kernel - Re: RFC: Reproducible oops with lockdep on count_matching

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Date:	Mon, 5 Nov 2007 15:56:22 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Michael Buesch" <mb@...sch.de>
Cc:	"Peter Zijlstra" <peterz@...radead.org>,
	"Luis R. Rodriguez" <mcgrof@...il.com>,
	"Michael Wu" <flamingice@...rmilk.net>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"John W. Linville" <linville@...driver.com>,
	"Ingo Molnar" <mingo@...hat.com>,
	"Johannes Berg" <johannes@...solutions.net>,
	linux-kernel@...r.kernel.org, "Michael Chan" <mchan@...adcom.com>,
	netdev@...r.kernel.org, "Christoph Lameter" <clameter@....com>
Subject: Re: RFC: Reproducible oops with lockdep on count_matching_names()

Hi Michael,

On Monday 05 November 2007 13:23:50 Pekka Enberg wrote:
> > Is CONFIG_DEBUG_SLAB enabled? Usually these kind of random corruptions
> > are caused by someone passing a bad pointer to kfree() or
> > kmem_cache_free().

On 11/5/07, Michael Buesch <mb@...sch.de> wrote:
> Yeah.
>
> What I also saw was random "one-bit-errors" once and then on rmmod of modules.
> I have absolutely no idea how they were caused, though (I read the freeing
> codes of the stuff hundreds of times). I don't have any of the oops messages
> anymore.
> But I do _not_ see this behaviour with slub anymore.

It is possible that the corruption is still there but SLUB doesn't
show it. Have you tried with slub_debug enabled?

Anyway, looking at the oops:

> BUG: unable to handle kernel paging request at virtual address f88a4a05
> printing eip: f88a4a05 *pde = 02000067 *pte = 00000000
>
> EIP: 0060:[<f88a4a05>] EFLAGS: 00010086 CPU: 0
> EIP is at 0xf88a4a05
> EAX: c20b75c8 EBX: c2f86f38 ECX: f88a4a05 EDX: c2f86f38
> ESI: c20b75c8 EDI: c2f89c00 EBP: c3897bfc ESP: c3897be0
>  DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
> Process modprobe (pid: 2908, ti=c3896000 task=c3935150 task.ti=c3896000)
> Stack: c01b2afc c2f82d98 c3897bf4 c01ba8b6 c2f86f38 c20b75c8 c2f82c00 c3897c24
>       c02186dd c2f86f38 c3897c24 c01b54c0 c20b75c8 00000001 c20b75c8 c2f86f38
>       c20b75c8 c3897c30 c01b54ed 00000001 c3897c54 c01b556c 00000001 c3897cd4
> Call Trace:
>  [<c0104cec>] show_trace_log_lvl+0x1a/0x2f
>  [<c0104d9e>] show_stack_log_lvl+0x9d/0xa5
>  [<c0104e53>] show_registers+0xad/0x17c
>  [<c0105017>] die+0xf5/0x1c6
>  [<c0112715>] do_page_fault+0x450/0x537
>  [<c02a835a>] error_code+0x6a/0x70
>  [<c02186dd>] scsi_request_fn+0x5f/0x2ec
>  [<c01b54ed>] __generic_unplug_device+0x20/0x23

We jump to a bogus address 0xf88a4a05 via a function pointer from
scsi_request_fn(). Can you work out the exact file and line for
scsi_request_fn+0x5f (look for "gdb vmlinux" in
Documentation/BUG-HUNTING) please?

                                                   Pekka
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