Re: [BUG] 2.5.65-mm3 kernel BUG at fs/ext3/super.c:1795!

Alexander Hoogerhuis [off-list ref] wrote:

Andrew Morton [off-list ref] writes:

quoted

[SNIP]

Disk I/O on my machine froze up during very light work after a few
hours, luckily I had a window open on another machine so I could do a
simple capture and save the info:

kernel BUG at fs/ext3/super.c:1795!
invalid operand: 0000 [#1]
CPU:    0
EIP:    0060:[<c018b522>]    Not tainted VLI
EFLAGS: 00010246
EIP is at ext3_write_super+0x36/0x94
eax: 00000000   ebx: c8834000   ecx: efb5904c   edx: efb59000
esi: efb59000   edi: c8834000   ebp: c8835ecc   esp: c8835ec0
ds: 007b   es: 007b   ss: 0068
Process pdflush (pid: 7853, threadinfo=c8834000 task=ed0a5880)
Stack: c8835ee4 00000287 efb5904c c8835ee4 c0153148 efb59000 00000077 51eb851f
       c8835fcc c8835fa4 c0137fd0 c03892fc 007b9f47 007b168f 00000000 00000000
       c8835ef4 00000000 00000001 00000000 00000001 00000000 00000053 00000000
Call Trace:
 [<c0153148>] sync_supers+0xde/0xea
 [<c0137fd0>] wb_kupdate+0x68/0x161
 [<c0118985>] schedule+0x1a4/0x3ac
 [<c01386e8>] __pdflush+0xdc/0x1d8
 [<c01387e4>] pdflush+0x0/0x15
 [<c01387f5>] pdflush+0x11/0x15
 [<c0137f68>] wb_kupdate+0x0/0x161
 [<c0108e69>] kernel_thread_helper+0x5/0xb

How on earth did you do that?

sync_supers() does lock_super, then calls ext3_write_super.

ext3_write_super() does a down_trylock() on sb->s_lock and goes BUG
if it acquired the lock.

So you've effectively done this:

	down(&sem);
	if (down_trylock(&sem))
		BUG();

This can only be a random memory scribble, a hardware bug or a
preempt-related bug in down_trylock().

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