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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/ # v1
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

authored by

David Howells and committed by
Linus Torvalds 2aeb8c86 978df3e1

+13 -1
+13 -1
fs/afs/inode.c
··· 740 740 { 741 741 struct inode *inode = d_inode(path->dentry); 742 742 struct afs_vnode *vnode = AFS_FS_I(inode); 743 - int seq = 0; 743 + struct key *key; 744 + int ret, seq = 0; 744 745 745 746 _enter("{ ino=%lu v=%u }", inode->i_ino, inode->i_generation); 747 + 748 + if (!(query_flags & AT_STATX_DONT_SYNC) && 749 + !test_bit(AFS_VNODE_CB_PROMISED, &vnode->flags)) { 750 + key = afs_request_key(vnode->volume->cell); 751 + if (IS_ERR(key)) 752 + return PTR_ERR(key); 753 + ret = afs_validate(vnode, key); 754 + key_put(key); 755 + if (ret < 0) 756 + return ret; 757 + } 746 758 747 759 do { 748 760 read_seqbegin_or_lock(&vnode->cb_lock, &seq);