linux-kernel - Re: kernel BUG at lib/radix-tree.c:473!

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Message-ID: <Pine.LNX.4.64.0808141347480.11013@blonde.site>
Date:	Thu, 14 Aug 2008 14:06:56 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Ian Campbell <ijc@...lion.org.uk>
cc:	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Kel Modderman <kel@...ku42.de>
Subject: Re: kernel BUG at lib/radix-tree.c:473!

On Thu, 14 Aug 2008, Ian Campbell wrote:
> Jeremy first noticed this
> http://marc.info/?l=linux-kernel&m=121783008503477&w=2
> 
> [    3.132333] ------------[ cut here ]------------
> [    3.132343] kernel BUG at /home/ijc/development/kernel/2.6.git/lib/radix-tree.c:473!
> [    3.132348] invalid opcode: 0000 [#1] SMP 
> [    3.132352] Modules linked in:
> [    3.132356] 
> [    3.132363] Pid: 580, comm: debconf Tainted: G        W (2.6.26 #27)
> [    3.132368] EIP: 0061:[<c01f5279>] EFLAGS: 00010002 CPU: 0
> [    3.132375] EIP is at radix_tree_tag_set+0x1d/0x9f
> [    3.132379] EAX: c203af30 EBX: c261b8c0 ECX: 00000000 EDX: 00000001
> [    3.132383] ESI: 00000000 EDI: 00000001 EBP: c7977ce8 ESP: c7977cc8
> [    3.132387]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0069
> [    3.132392] Process debconf (pid: 580, ti=c7976000 task=c538a240 task.ti=c7976000)
> [    3.132396] Stack: fffede22 00000000 00000001 c203af30 c203af2c c261b8c0 c203af2c 00000001 
> [    3.132406]        c7977cfc c01a1570 c261b8c0 c203af2c c2563000 c7977d0c c01a1a24 c261b8c0 
> [    3.132416]        00000001 c7977d1c c01682fc c261b8c0 00000001 c7977d2c c0169185 c261b8c0 
> [    3.132425] Call Trace:
> [    3.132428]  [<c01a1570>] ? __set_page_dirty+0xdf/0x11f
> [    3.132434]  [<c01a1a24>] ? __set_page_dirty_buffers+0x68/0x6c
> [    3.132441]  [<c01682fc>] ? set_page_dirty+0x34/0x94
> [    3.132446]  [<c0169185>] ? set_page_dirty_balance+0xe/0x3c
> [    3.132452]  [<c016eec6>] ? __do_fault+0x35d/0x37e
> [    3.132458]  [<c01707a4>] ? handle_mm_fault+0x45d/0x9c9
> [    3.132463]  [<c01939a0>] ? __d_lookup+0xb7/0xeb
> [    3.132469]  [<c0180d18>] ? kfree+0x81/0x88
> [    3.132474]  [<c02dfaf7>] ? _spin_unlock_irqrestore+0x19/0x1f
> [    3.132481]  [<c02dfaf7>] ? _spin_unlock_irqrestore+0x19/0x1f
> [    3.132487]  [<c011b5ee>] ? do_page_fault+0x3be/0x8d0
> [    3.132493]  [<c02061ef>] ? fb_ioctl+0x1a2/0x2de
> [    3.132499]  [<c011ad1c>] ? pvclock_clocksource_read+0x48/0xa3
> [    3.132506]  [<c02dfaf7>] ? _spin_unlock_irqrestore+0x19/0x1f
> [    3.132512]  [<c013e02b>] ? hrtimer_start+0x12a/0x144
> [    3.132519]  [<c0104682>] ? xen_mc_flush+0x123/0x160
> [    3.132525]  [<c0104699>] ? xen_mc_flush+0x13a/0x160
> [    3.136027]  [<c010436c>] ? xen_leave_lazy+0x12/0x14
> [    3.136027]  [<c01075bc>] ? __switch_to+0xec/0x126
> [    3.136027]  [<c012755c>] ? finish_task_switch+0x32/0xa5
> [    3.136027]  [<c02de601>] ? schedule+0x6cc/0x735
> [    3.136027]  [<c018e377>] ? vfs_ioctl+0x57/0x69
> [    3.136027]  [<c018e636>] ? sys_ioctl+0x50/0x5a
> [    3.136027]  [<c011b230>] ? do_page_fault+0x0/0x8d0
> [    3.136027]  [<c02dfd3a>] ? error_code+0x72/0x78
> [    3.136027]  =======================
> [    3.136027] Code: b4 89 42 04 83 c4 50 89 d8 5b 5e 5f 5d c3 55 89 e5 57 56 53 83 ec 14 89 45 ec 89 55 e8 89 4d e4 8b 30 3b 14 b5 88 52 3a c0 76 04 <0f> 0b eb fe 8b 45 ec 8b 4d e4 8b 58 08 6b c6 06 c1 e1 03 
> [    3.136027] EIP: [<c01f5279>] radix_tree_tag_set+0x1d/0x9f SS:ESP 0069:c7977cc8
> [    3.136027] ---[ end trace 991579adcab01bbf ]---
> 
> I've bisected it down to:
> commit 14fcc23fdc78e9d32372553ccf21758a9bd56fa1
> Author: Hugh Dickins <hugh@...itas.com>
> Date:   Mon Jul 28 15:46:19 2008 -0700
> 
>     tmpfs: fix kernel BUG in shmem_delete_inode
> 
> Reverting this patch from current Linus tree
> (b635acec48bcaa9183fcbf4e3955616b0d4119b5) causes the problem to go
> away. I haven't yet seen the link between the backtrace and this
> changeset though.

Nor I!  Thanks a lot for doing the bisection, but all I can say so far
is that I'm utterly flummoxed.  (And I do wonder if it's a pvfb bug
which has previously been masked; but that's premature, we can't
say until we understand how it got here at all.)

There's a lot of "?" entries in your backtrace, Jeremy's ones
look clearer: CONFIG_FRAME_POINTER=y ought to improve yours.

In both cases it's handling a page fault: I'm curious as to what kind
of vma this fault is occurring on.  Could you devise a way of getting
us /proc/<pid>/maps output, together with the faulting address, when
it hits one of these BUGs?  Or should I try to put together a patch
for that?

Hugh
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