Re: 2.6.39-rc7 BUG in fs/namei.c:1362, bisected -- BKL, symlinks, and rename

[Arnd Bergmann <arnd@arndb.de>]

On Saturday 14 May 2011, Erez Zadok wrote:
> 
> Today 18:56:09
>    
> Easily reproducible bug found in v2.6.39-rc7-174-gddb503b. This line in fs/namei.c:nested_symlink() is triggered:
> 
>         BUG_ON(nd->depth >= MAX_NESTED_LINKS);
> 
> To reproduce: run racer on any f/s.  I narrowed it down to just 'rename' and 'symlink' ops (verified that other ops aren't involved).
> 
> Bisection narrowed the bug down to this one commit:

Hi Erez,

Thanks for the report and the work you put into bisecting it.

> commit f74b9444192c60603020c61d7915b72893137edc
> Merge: 7a63628 4ba8216
> Author: Linus Torvalds <torvalds@linux-foundation.org>
> Date:   Wed Mar 16 17:21:00 2011 -0700
> 
>     Merge branch 'config' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl
>     
>     * 'config' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl:
>       BKL: That's all, folks
>       fs/locks.c: Remove stale FIXME left over from BKL conversion
>       ipx: remove the BKL
>       appletalk: remove the BKL
>       x25: remove the BKL
>       ufs: remove the BKL
>       hpfs: remove the BKL
>       drivers: remove extraneous includes of smp_lock.h
>       tracing: don't trace the BKL
>       adfs: remove the big kernel lock
> 
> I'm happy to test a fix if someone has one for me.  I suspect that once BKL was removed, some lock might
> now be missing somewhere in the VFS that relates to rename/symlink/lookup.  I'll keep digging.

As the above commit is a merge commit, it seems an unlikely candidate for causing the bug. That would
indicate that something went wrong with Linus merging my patches, which I find less likely than
a bug in one of my patches.

Are you 100% sure that 4ba8216cd9 "BKL: That's all, folks" is actually working while the merged
commit f74b94441 is broken?

	Arnd