linux-kernel - Re: 2.6.21-git11: BUG in loop.ko

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Message-Id: <20070509170521.ec2c9ae7.akpm@linux-foundation.org>
Date:	Wed, 9 May 2007 17:05:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ken Chen <kenchen@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Alexey Dobriyan <adobriyan@...ru>
Subject: Re: 2.6.21-git11: BUG in loop.ko

On Wed, 09 May 2007 16:52:41 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Seems to be getting a 0 refcount.  I don't see anything in the recent
> changes which might cause this, but this is relatively new behaviour. 
> It was working for me in the 2.6.21-pre time period, but I haven't tried
> this since 2.6.21 was released.
> 
> The BUG is actually triggered by the __module_get(THIS_MODULE) in
> loop_set_fd.
> 
>     J
> 
> loop: module loaded
> device-mapper: ioctl: 4.11.0-ioctl (2006-10-12) initialised: dm-devel@...hat.com
> ------------[ cut here ]------------
> kernel BUG at /home/jeremy/hg/xen/paravirt/linux/include/linux/module.h:396!
> invalid opcode: 0000 [#1]
> PREEMPT SMP 
> Modules linked in: dm_snapshot dm_mod loop
> CPU:    1
> EIP:    0061:[<d085a911>]    Not tainted VLI
> EFLAGS: 00010246   (2.6.21-paravirt #1339)
> EIP is at lo_ioctl+0x65/0xa52 [loop]
> eax: 00000000   ebx: cfb92c98   ecx: d085e480   edx: 00000200
> esi: 00004c00   edi: cf8ad428   ebp: cf37fdc0   esp: cf37fbf8
> ds: 007b   es: 007b   fs: 00d8  gs: 0033  ss: 0069
> Process losetup (pid: 440, ti=cf37e000 task=cf30b4d0 task.ti=cf37e000)
> Stack: c1390080 c1390080 cf37fc10 00000008 cf8ad428 cfbb2258 00000000 cf37fc34 
>        c01458c5 cfb92c98 c1392a40 cf30ba70 cf30b4d0 cf30ba54 00000002 cf30ba70 
>        cf30b4d0 cf30ba54 00000002 00000003 c134c088 c134c088 cf37fc90 c01215b8 
> Call Trace:
>  [<c0109173>] show_trace_log_lvl+0x1a/0x30
>  [<c0109226>] show_stack_log_lvl+0x9d/0xa5
>  [<c0109425>] show_registers+0x1f7/0x336
>  [<c010967d>] die+0x119/0x21b
>  [<c0382c78>] do_trap+0x8a/0xa4
>  [<c0109ad1>] do_invalid_op+0x88/0x92
>  [<c0382a42>] error_code+0x72/0x78
>  [<c0211c79>] blkdev_driver_ioctl+0x4c/0x5d
>  [<c02123de>] blkdev_ioctl+0x754/0x7a2
>  [<c0198840>] block_ioctl+0x1b/0x1f
>  [<c0182e2e>] do_ioctl+0x22/0x68
>  [<c01830a6>] vfs_ioctl+0x232/0x245
>  [<c0183102>] sys_ioctl+0x49/0x63
>  [<c0108080>] syscall_call+0x7/0xb
>  =======================
> Code: ff 83 f8 06 0f 87 5a 09 00 00 ff 24 85 5c bc 85 d0 8b 9b cc 01 00 00 b8 80 e4 85 d0 89 9d 5c fe ff ff e8 37 0a 8f ef 85 c0 75 04 <0f> 0b eb fe b8 01 00 00 00 e8 79 9f 8c ef e8 ec 4b 9c ef c1 e0 
> EIP: [<d085a911>] lo_ioctl+0x65/0xa52 [loop] SS:ESP 0069:cf37fbf8
> 

A few people have been playing with module refcounting lately.  Did you
work out a reproduce-it recipe?
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