[PATCH 2/4] afs: Fix post-setattr file edit to do truncation correctly

[David Howells]

At the end of an kAFS RPC operation, there is an "edit" phase (originally
intended for post-directory modification ops to edit the local image) that
the setattr VFS op uses to fix up the pagecache if the RPC that requested
truncation of a file was successful.

afs_setattr_edit_file() calls truncate_setsize() which sets i_size, expands
the pagecache if needed and truncates the pagecache.  The first two of
those, however, are redundant as they've already been done by
afs_setattr_success() under the io_lock and the first is also done under
the callback lock (cb_lock).

Fix afs_setattr_edit_file() to call truncate_pagecache() instead (which is
called by truncate_setsize(), thereby skipping the redundant parts.

Fixes: 100ccd18bb41 ("netfs: Optimise away reads above the point at which there can be no data")
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Matthew Wilcox (Oracle) <willy at infradead.org>
cc: Pankaj Raghav <p.raghav at samsung.com>
cc: Jeff Layton <jlayton at kernel.org>
cc: Marc Dionne <marc.dionne at auristor.com>
cc: linux-afs at lists.infradead.org
cc: netfs at lists.linux.dev
cc: linux-mm at kvack.org
cc: linux-fsdevel at vger.kernel.org
---
 fs/afs/inode.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 3acf5e050072..a95e77670b49 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -695,13 +695,18 @@ static void afs_setattr_edit_file(struct afs_operation *op)
 {
 	struct afs_vnode_param *vp = &op->file[0];
 	struct afs_vnode *vnode = vp->vnode;
+	struct inode *inode = &vnode->netfs.inode;
 
 	if (op->setattr.attr->ia_valid & ATTR_SIZE) {
 		loff_t size = op->setattr.attr->ia_size;
-		loff_t i_size = op->setattr.old_i_size;
+		loff_t old = op->setattr.old_i_size;
+
+		/* Note: inode->i_size was updated by afs_apply_status() inside
+		 * the I/O and callback locks.
+		 */
 
-		if (size != i_size) {
-			truncate_setsize(&vnode->netfs.inode, size);
+		if (size != old) {
+			truncate_pagecache(inode, size);
 			netfs_resize_file(&vnode->netfs, size, true);
 			fscache_resize_cookie(afs_vnode_cache(vnode), size);
 		}