Chandru <[email protected]> writes:
> Eric W. Biederman wrote:
>> You certain seem to be in one of the proc stress conditions so this
>> may not be a unique bug.
>>
>> Digging through the disassembly and figuring out which access you died
>> on would be interesting, so we could know with precision which part
>> of tid_fd_revalidate we are dying in. My ppc64 isn't good enough especially
>> without the matching binaries to figure that out though.
>> All I know is that you are about 25 instructions into
>> tid_fd_revalidate.
>>
> From the disassembly in xmon, the code that failed while running was in
> fcheck_files() called from tid_fd_revalidate()
> Further the contents of 'struct files_struct *files' were all filled with
> '0x6b's. I tried to look in to for which task the lookup was being done and the
> task seemed to be 'execve04'. Also noticed that another cpu ( cpu #1) was
> running on an execve code path ( do not have the state of the system right now
> to copy it's backtrace :( ).
Which kernel version did you say you were running.
This appears to be a case of calling put_files_struct without changing
the pointer in the task_struct. So we are reading a stale pointer
in get_files_struct.
It looks like the patch below added fixed a bug that has the same symptoms
as what you are describing. So I suspect this is fixed in linus's tree
already.
>commit 3b9b8ab65d8eed784b9164d03807cb2bda7b5cd6
>Author: Kirill Korotaev <[email protected]>
>Date: Fri Sep 29 02:00:05 2006 -0700
>
> [PATCH] Fix unserialized task->files changing
>
> Fixed race on put_files_struct on exec with proc. Restoring files on
> current on error path may lead to proc having a pointer to already kfree-d
> files_struct.
>
> ->files changing at exit.c and khtread.c are safe as exit_files() makes all
> things under lock.
>
> Found during OpenVZ stress testing.
>
> [[email protected]: add export]
> Signed-off-by: Pavel Emelianov <[email protected]>
> Signed-off-by: Kirill Korotaev <[email protected]>
> Signed-off-by: Andrew Morton <[email protected]>
> Signed-off-by: Linus Torvalds <[email protected]>
Eric
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