afs: Fix afs_getattr() to refetch file status if callback break occurred

If a callback break occurs (change notification), afs_getattr() needs to
issue an FS.FetchStatus RPC operation to update the status of the file
being examined by the stat-family of system calls.

Fix afs_getattr() to do this if AFS_VNODE_CB_PROMISED has been cleared
on a vnode by a callback break.  Skip this if AT_STATX_DONT_SYNC is set.

This can be tested by appending to a file on one AFS client and then
using "stat -L" to examine its length on a machine running kafs.  This
can also be watched through tracing on the kafs machine.  The callback
break is seen:

     kworker/1:1-46      [001] .....   978.910812: afs_cb_call: c=0000005f YFSCB.CallBack
     kworker/1:1-46      [001] ...1.   978.910829: afs_cb_break: 100058:23b4c:242d2c2 b=2 s=1 break-cb
     kworker/1:1-46      [001] .....   978.911062: afs_call_done:    c=0000005f ret=0 ab=0 [0000000082994ead]

And then the stat command generated no traffic if unpatched, but with
this change a call to fetch the status can be observed:

            stat-4471    [000] .....   986.744122: afs_make_fs_call: c=000000ab 100058:023b4c:242d2c2 YFS.FetchStatus
            stat-4471    [000] .....   986.745578: afs_call_done:    c=000000ab ret=0 ab=0 [0000000087fc8c84]

Fixes: 08e0e7c82eea ("[AF_RXRPC]: Make the in-kernel AFS filesystem use AF_RXRPC.")
Reported-by: Markus Suvanto <markus.suvanto@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Tested-by: Markus Suvanto <markus.suvanto@gmail.com>
Tested-by: kafs-testing+fedora34_64checkkafs-build-496@auristor.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216010
Link: https://lore.kernel.org/r/165308359800.162686.14122417881564420962.stgit@warthog.procyon.org.uk/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 2fe402483ad5bbc59750e2096f7127a3ba2152c0..30b066299d39f70a450539823dbe75602427e81a 100644 (file)
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -740,10 +740,22 @@ int afs_getattr(struct user_namespace *mnt_userns, const struct path *path,
 {
        struct inode *inode = d_inode(path->dentry);
        struct afs_vnode *vnode = AFS_FS_I(inode);
-       int seq = 0;
+       struct key *key;
+       int ret, seq = 0;
 
        _enter("{ ino=%lu v=%u }", inode->i_ino, inode->i_generation);
 
+       if (!(query_flags & AT_STATX_DONT_SYNC) &&
+           !test_bit(AFS_VNODE_CB_PROMISED, &vnode->flags)) {
+               key = afs_request_key(vnode->volume->cell);
+               if (IS_ERR(key))
+                       return PTR_ERR(key);
+               ret = afs_validate(vnode, key);
+               key_put(key);
+               if (ret < 0)
+                       return ret;
+       }
+
        do {
                read_seqbegin_or_lock(&vnode->cb_lock, &seq);
                generic_fillattr(&init_user_ns, inode, stat);