On Wed, 2007-11-14 at 16:41 -0500, Trond Myklebust wrote: > On Wed, 2007-11-14 at 22:31 +0100, Peter Zijlstra wrote: > > On Wed, 2007-11-14 at 22:22 +0100, Nick Piggin wrote: > > > On Wed, Nov 14, 2007 at 09:01:39PM +0100, Peter Zijlstra wrote: > > > > Normal locking order is: > > > > > > > > i_mutex > > > > mmap_sem > > > > > > > > However NFS's ->mmap hook, which is called under mmap_sem, can take i_mutex. > > > > Avoid this potential deadlock by doing the work that requires i_mutex from > > > > the new ->mmap_prepare(). > > > > > > > > [ Is this sufficient, or does it introduce a race? ] > > > > > > Seems like an OK patchset in my opinion. I don't know much about NFS > > > unfortunately, but I wonder what prevents the condition fixed by > > > nfs_revalidate_mapping from happening again while the mmap is active...? > > > > As the changelog might have suggested, I'm not overly sure of the nfs > > requirements myself. I think it just does a best effort at getting the > > pages coherent with other clients, and then hopes for the best. > > > > I'll let Trond enlighten us further before I make an utter fool of > > myself :-) > > The NFS client needs to check the validity of already cached data before > it allows those pages to be mmapped. If it finds out that the cache is > stale, then we need to call invalidate_inode_pages2() to clear out the > cache and refresh it from the server. The inode->i_mutex is necessary in > order to prevent races between the new writes and the cache invalidation > code. Right, but I guess what Nick asked is, if pages could be stale to start with, how is that avoided in the future. The way I understand it, this re-validate is just a best effort at getting a coherent image. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
