Re: [PATCH] vfs namespace: Don't assume mount namespace has valid root

[Sasha Levin]

On Wed, Mar 14, 2012 at 11:37 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> On Wed, Mar 14, 2012 at 11:03:43PM +0200, Sasha Levin wrote:
>> > And that's all pointers to mnt_namespace that ever exist, aside of function
>> > arguments and local variables. ?I'm not saying that I couldn't have possibly
>> > fucked it up, but from rereading that code it doesn't look like we could
>> > end up with dangling pointers to already freed instances...
>>
>> I'm trying to find the exact chain of events leading it it at the
>> moment, but it reproduces rather easily - so if you have any ideas on
>> figuring it out I'm happy to try anything.
>
> Which kernel, for starters?  I'd probably add dumping call chain +
> return value in alloc_mnt_ns(), call chain + pointer being freed in
> final put_mnt_ns() and failure exit of dup_mnt_ns(), address of
> mnt_ns and value assigned to ->root on assignments to ->root in
> create_mnt_ns() and dup_mnt_ns() and mnt_ns in dup_mnt_ns() if it
> happens to have NULL ->root.
>
> That should give you full history of allocation/freeing mnt_namespace
> instances and of assignments to anyone's ->root.  Ought to make a sane
> starting point...

I'm running 3.3.0-rc6-next-20120309-sasha-00002-g8fd19a0.

I found that if I revert f8b88187 ("brlocks/lglocks: cleanups") it
seems that the problem is gone.
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