linux-kernel - Re: 2.6.20.3: kernel BUG at mm/slab.c:597 try#2

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Date:	Mon, 19 Mar 2007 10:32:00 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Andreas Steinmetz" <ast@...dv.de>,
	"Linux Kernel Mailinglist" <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org
Subject: Re: 2.6.20.3: kernel BUG at mm/slab.c:597 try#2

On 3/19/07, Pekka Enberg <penberg@...helsinki.fi> wrote:
> EIP is at kmem_cache_free+0x29/0x5a
> eax: c1800000   ebx: f0ae12c0   ecx: c18f73c0   edx: c1800000
> esi: c1919de0   edi: 00000000   ebp: 00001000   esp: f1fe7e14
> ds: 007b   es: 007b   ss: 0068
>
> But somehow eax and edx have the same value 0xc1800000 here. Hmm?

Aah, but if you look at contents of the stack:

Stack: f0ae12c0 c1919de0 ffffffea c0137f97 00000000 f0ae12c0 c1919e20 c0168d45
       f0ae12c0 00001000 c0168fb9 c02a77e3 00001000 00000000 00000000 00000000
       00000000 c17bb6e0 00001000 00000000 f1b38be8 00000003 f54ac050 c1b9d6e8
Call Trace:
 [<c0137f97>] mempool_free+0x48/0x4c
 [<c0168d45>] bio_free+0x21/0x2c
 [<c0168fb9>] bio_put+0x22/0x23

You can see that mempool_free is passing a NULL pointer to
kmem_cache_free() which doesn't handle it properly. The NULL pointer
comes from bio_free() where ->bi_io_vec is  NULL because nr_iovecs
passed to bio_alloc_bioset() was zero.

The question is, why is nr_pages zero in scsi_req_map_sg()?
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