From 779eafab06036fe1e06dea9bbd97cc4b12f0138f Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Fri, 18 Aug 2017 17:12:52 +1000 Subject: [PATCH] NFS: flush data when locking a file to ensure cache coherence for mmap. When a byte range lock (or flock) is taken out on an NFS file, the validity of the cached data is checked and the inode is marked NFS_INODE_INVALID_DATA. However the cached data isn't flushed from the page cache. This is sufficient for future read() requests or mmap() requests as they call nfs_revalidate_mapping() which performs the flush if necessary. However an existing mapping is not affected. Accessing data through that mapping will continue to return old data even though the inode is marked NFS_INODE_INVALID_DATA. This can easily be confirmed using the 'nfs' tool in git://github.com/okirch/twopence-nfs.git and running nfs coherence FILENAME on one client, and nfs coherence -r FILENAME on another client. It appears that prior to Linux 2.6.0 this worked correctly. However commit: http://git.kernel.org/cgit/linux/kernel/git/history/history.git/commit/?id=ca9268fe3ddd075714005adecd4afbd7f9ab87d0 removed the call to inode_invalidate_pages() from nfs_zap_caches(). I haven't tested this code, but inspection suggests that prior to this commit, file locking would invalidate all inode pages. This patch adds a call to nfs_revalidate_mapping() after a successful SETLK so that invalid data is flushed. With this patch the above test passes. To minimize impact (and possibly avoid a GETATTR call) this only happens if the mapping might be mapped into userspace. Cc: Olaf Kirch Signed-off-by: NeilBrown Signed-off-by: Trond Myklebust --- fs/nfs/file.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/nfs/file.c b/fs/nfs/file.c index af330c31f627..1d71472d239d 100644 --- a/fs/nfs/file.c +++ b/fs/nfs/file.c @@ -744,15 +744,18 @@ do_setlk(struct file *filp, int cmd, struct file_lock *fl, int is_local) goto out; /* - * Revalidate the cache if the server has time stamps granular - * enough to detect subsecond changes. Otherwise, clear the - * cache to prevent missing any changes. + * Invalidate cache to prevent missing any changes. If + * the file is mapped, clear the page cache as well so + * those mappings will be loaded. * * This makes locking act as a cache coherency point. */ nfs_sync_mapping(filp->f_mapping); - if (!NFS_PROTO(inode)->have_delegation(inode, FMODE_READ)) + if (!NFS_PROTO(inode)->have_delegation(inode, FMODE_READ)) { nfs_zap_caches(inode); + if (mapping_mapped(filp->f_mapping)) + nfs_revalidate_mapping(inode, filp->f_mapping); + } out: return status; } -- 2.30.2