Re: [patch] nfs: fix locking in nfs/inode.c in nfs_free_open_context

Arnd Bergmann
2007-07-26T11:24:21Z

On Wednesday 25 July 2007, Trond Myklebust wrote:
>
> On Wed, 2007-07-25 at 17:08 +0200, Christian Krafft wrote:
>
> > Obviously the locking code in nfs_free_open_context is wrong.
> > Checking the list for entries and removing the entry should be an atomic operation.
>
> Wrong. It is quite safe to test the structure member ctx->list for
> emptiness outside the spinlock because we have an explicit guarantee
> that nobody else has a reference to this structure, plus the
> atomic_dec_and_test() in kref_put() has acted as a memory barrier for
> us.

Well, the real question then is how the ctx can still be present in the
nfsi->open_files list. Since we are in nfs_free_open_context(), there
must not be any pointer to the ctx anywhere, but still we have this other
thread calling get_nfs_open_context() on it.