linux/fs/afs
David Howells 22650f1481 afs: Fix speculative status fetches
The generic/464 xfstest causes kAFS to emit occasional warnings of the
form:

        kAFS: vnode modified {100055:8a} 30->31 YFS.StoreData64 (c=6015)

This indicates that the data version received back from the server did not
match the expected value (the DV should be incremented monotonically for
each individual modification op committed to a vnode).

What is happening is that a lookup call is doing a bulk status fetch
speculatively on a bunch of vnodes in a directory besides getting the
status of the vnode it's actually interested in.  This is racing with a
StoreData operation (though it could also occur with, say, a MakeDir op).

On the client, a modification operation locks the vnode, but the bulk
status fetch only locks the parent directory, so no ordering is imposed
there (thereby avoiding an avenue to deadlock).

On the server, the StoreData op handler doesn't lock the vnode until it's
received all the request data, and downgrades the lock after committing the
data until it has finished sending change notifications to other clients -
which allows the status fetch to occur before it has finished.

This means that:

 - a status fetch can access the target vnode either side of the exclusive
   section of the modification

 - the status fetch could start before the modification, yet finish after,
   and vice-versa.

 - the status fetch and the modification RPCs can complete in either order.

 - the status fetch can return either the before or the after DV from the
   modification.

 - the status fetch might regress the locally cached DV.

Some of these are handled by the previous fix[1], but that's not sufficient
because it checks the DV it received against the DV it cached at the start
of the op, but the DV might've been updated in the meantime by a locally
generated modification op.

Fix this by the following means:

 (1) Keep track of when we're performing a modification operation on a
     vnode.  This is done by marking vnode parameters with a 'modification'
     note that causes the AFS_VNODE_MODIFYING flag to be set on the vnode
     for the duration.

 (2) Alter the speculation race detection to ignore speculative status
     fetches if either the vnode is marked as being modified or the data
     version number is not what we expected.

Note that whilst the "vnode modified" warning does get recovered from as it
causes the client to refetch the status at the next opportunity, it will
also invalidate the pagecache, so changes might get lost.

Fixes: a9e5c87ca7 ("afs: Fix speculative status fetch going out of order wrt to modifications")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-and-reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/160605082531.252452.14708077925602709042.stgit@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/linux-fsdevel/161961335926.39335.2552653972195467566.stgit@warthog.procyon.org.uk/ # v1
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-01 11:55:36 -07:00
..
addr_list.c afs: Use kfree_rcu() instead of casting kfree() to rcu_callback_t 2020-03-13 10:47:33 -07:00
afs_cm.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
afs_fs.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
afs_vl.h afs: Implement client support for the YFSVL.GetCellName RPC op 2020-06-04 15:37:57 +01:00
afs.h afs: Implement client support for the YFSVL.GetCellName RPC op 2020-06-04 15:37:57 +01:00
cache.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
callback.c afs: Fix the by-UUID server tree to allow servers with the same UUID 2020-06-04 15:37:57 +01:00
cell.c afs: Fix tracing deref-before-check 2020-10-27 22:05:56 +00:00
cmservice.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
dir_edit.c afs: Fix directory entry size calculation 2021-01-04 12:25:19 +00:00
dir_silly.c afs: Fix speculative status fetches 2021-05-01 11:55:36 -07:00
dir.c afs: Fix speculative status fetches 2021-05-01 11:55:36 -07:00
dynroot.c afs: Add tracing for cell refcount and active user count 2020-10-16 14:39:21 +01:00
file.c afs: Use the netfs_write_begin() helper 2021-04-23 10:17:28 +01:00
flock.c afs: Remove erroneous fallthough annotation 2020-08-27 14:33:01 -05:00
fs_operation.c afs: Fix speculative status fetches 2021-05-01 11:55:36 -07:00
fs_probe.c rxrpc: Make rxrpc_kernel_get_srtt() indicate validity 2020-08-20 18:21:28 +01:00
fsclient.c afs: Use new netfs lib read helper API 2021-04-23 10:17:28 +01:00
inode.c afs: Fix speculative status fetches 2021-05-01 11:55:36 -07:00
internal.h afs: Fix speculative status fetches 2021-05-01 11:55:36 -07:00
Kconfig afs: Use new netfs lib read helper API 2021-04-23 10:17:28 +01:00
main.c rxrpc: Fix deadlock around release of dst cached on udp tunnel 2021-01-29 21:38:11 -08:00
Makefile afs: Detect cell aliases 1 - Cells with root volumes 2020-06-04 15:37:57 +01:00
misc.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
mntpt.c afs: Stop listxattr() from listing "afs.*" attributes 2021-03-15 17:09:54 +00:00
proc.c afs: Add tracing for cell refcount and active user count 2020-10-16 14:39:21 +01:00
protocol_uae.h afs: Add support for the UAE error table 2019-06-28 18:37:53 +01:00
protocol_yfs.h afs: Implement client support for the YFSVL.GetCellName RPC op 2020-06-04 15:37:57 +01:00
rotate.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
rxrpc.c afs: Use ITER_XARRAY for writing 2021-04-23 10:17:27 +01:00
security.c fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
server_list.c afs: Reorganise volume and server trees to be rooted on the cell 2020-06-04 15:37:57 +01:00
server.c afs: Don't assert on unpurgeable server records 2020-10-16 14:39:34 +01:00
super.c afs: Fix memory leak when mounting with multiple source parameters 2020-12-08 15:59:25 -08:00
vl_alias.c afs: Add tracing for cell refcount and active user count 2020-10-16 14:39:21 +01:00
vl_list.c afs: Don't use VL probe running state to make decisions outside probe code 2020-08-20 18:21:28 +01:00
vl_probe.c afs: Don't use VL probe running state to make decisions outside probe code 2020-08-20 18:21:28 +01:00
vl_rotate.c afs: Add tracing for cell refcount and active user count 2020-10-16 14:39:21 +01:00
vlclient.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
volume.c afs: Add tracing for cell refcount and active user count 2020-10-16 14:39:21 +01:00
write.c afs: Fix speculative status fetches 2021-05-01 11:55:36 -07:00
xattr.c afs: Stop listxattr() from listing "afs.*" attributes 2021-03-15 17:09:54 +00:00
xdr_fs.h afs: Fix directory entry size calculation 2021-01-04 12:25:19 +00:00
yfsclient.c afs: Use the fs operation ops to handle FetchData completion 2021-04-23 10:17:28 +01:00