afs: Fix post-setattr file edit to do truncation correctly

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@redhat.com>
Link: https://lore.kernel.org/r/20240823200819.532106-3-dhowells@redhat.com
cc: Matthew Wilcox (Oracle) <willy@infradead.org>
cc: Pankaj Raghav <p.raghav@samsung.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: netfs@lists.linux.dev
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 3acf5e0500728b44805fa3a8b0d18cf2e7a4bd0d..a95e77670b49450541ce6234fb8732586baf4608 100644 (file)
--- 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);
                }