Re: [autofs] Re: umount() and NFS races in 2.4.26

[Greg Banks <gnb@sgi.com>]

On Sat, Jul 10, 2004 at 02:57:46PM +0800, raven@themaw.net wrote:
> On Thu, 8 Jul 2004, Thomas Moestl wrote:
> > I believe that I have found two problems:
> > 
> > - The NFS async unlink code (fs/nfs/unlink.c) does keep a dentry for
> >   later asynchronous processing, but the mount point is unbusied via
> >   path_release() once sys_unlink() returns (fs/namei.c). [...]

This used to be a bug.  It was fixed in 2.4.26 with

http://linux.bkbits.net:8080/linux-2.4/diffs/fs/nfs/dir.c@1.13

What happens now is that the dentry and its inode are cleaned up
when the async unlink task is deleted in nfs_put_super() between
the first and second calls to invalidate_inodes() in kill_super().

> > - There is a SMP race between the shrink_dcache_parent() (fs/dcache.c)
> >   called from kill_super() and prune_dache() called via
> >   shrink_dache_memory() (called by kswapd), as follows: [...]

Your scenario sounds plausible and might explain at least some 
of the autofs unmount races we've been seeing.

> >   In the attached patch, I have used a semaphore to serialize purging
> >   accesses to the dentry_unused list. [...]

Can we see the patch please?

Greg.
-- 
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.