Re: [PATCH v2 1/4] cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC

[David Howells <dhowells@redhat.com>]

Frank Sorenson <sorenson@redhat.com> wrote:

> cifs_do_truncate() is invoked from cifs_open() without i_rwsem, so it
> cannot use cifs_resize_file_locked() to perform a proper fscache cookie
> resize.  Instead, add cifs_invalidate_cache() after cifs_setsize().
> 
> cifs_invalidate_cache() calls fscache_invalidate(), which works without
> holding i_rwsem: it unconditionally increments inval_counter and sets
> FSCACHE_COOKIE_NO_DATA_TO_READ, ensuring that stale cached data is not
> served once the cookie is later activated by fscache_use_cookie().
> Truncation to zero leaves no valid cached data, making invalidation the
> correct semantic here.

What happens if there's a concurrent read or write in another thread?
truncate(), buffered read/write and direct read/write() will play reasonably
with each other through a combination of i_rwsem and the stuff in
fs/netfs/locking.c.

But apart from that, I think that invalidating the cache should work.  It may
be slower, but since you're getting rid of all the data anyway...

David