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Date: Sat, 19 Feb 2011 23:54:31 -0500
From: Mark Lord <kernel@teksavvy.com>
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To: "Ted Ts'o" <tytso@mit.edu>, Linux Kernel <linux-kernel@vger.kernel.org>,
        linux-ext4@vger.kernel.org
Subject: Re: ext4 crash on 2.6.37: NULL ptr in ext4_discard_preallocations
References: <4D604620.9060204@teksavvy.com> <20110220000550.GA8765@thunk.org>
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On 11-02-19 07:05 PM, Ted Ts'o wrote:
> On Sat, Feb 19, 2011 at 05:37:20PM -0500, Mark Lord wrote:
>> 32-bit x86 system, 2.6.37 SMP kernel, Core2duo, 3.3GB RAM, no swap.
>>
>> The system just suddenly switched to fbconsole and dumped a traceback.
>> Here's the screen-shot photo:  http://rtr.ca/ext4_crash.jpg
>>
>> Is this a known bug that got fixed in 2.6.37.1 ?
> 
> No, this looks like a new one.
> 
> And I can't make the Code: line make sense.  Can you send me the
> fs/ext4/mballoc.s file after running the command "make
> fs/ext4/mballoc.s" in your build tree where you built this kernel?

Sent.  And here's an extract:

.globl ext4_discard_preallocations
        .type   ext4_discard_preallocations, @function
ext4_discard_preallocations:
        pushl   %ebp    #
        pushl   %edi    #
        leal    -136(%eax), %edi        #, ei
        pushl   %esi    #
        pushl   %ebx    #
        subl    $80, %esp       #,
        movl    172(%eax), %esi # <variable>.i_sb, sb
        movl    $0, 76(%esp)    #, group
        movzwl  122(%eax), %edx # <variable>.i_mode, tmp85
        andl    $61440, %edx    #, tmp85
        cmpl    $32768, %edx    #, tmp85
        jne     .L875   #,
        leal    68(%esp), %edx  #, tmp86
        leal    380(%eax), %ebx #, D.45176
        movl    %edx, 68(%esp)  # tmp86, list.next
        addl    $372, %eax      #,
        movl    %edx, 72(%esp)  # tmp86, list.prev
        movl    %eax, 28(%esp)  #, %sfp
.L876:
        movl    %ebx, %eax      # D.45176,
        call    _raw_spin_lock  #
        jmp     .L861   #
.L867:
        cmpl    %ebx, 60(%ebp)  # D.45176, <variable>.pa_obj_lock
        je      .L862   #,
#APP
# 3810 "fs/ext4/mballoc.c" 1
        1:      ud2

I wonder if the 003c offset is that "cmpl %ebx, 60(%ebp)" line?

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