When a subrequest is marked for needing retry, netfs will call
cifs_prepare_write() which will make cifs repick the server for the op
before renegotiating credits; it then calls cifs_issue_write() which
invokes smb2_async_writev() - which re-repicks the server.
If a different server is then selected, this causes the increment of
server->in_flight to happen against one record and the decrement to happen
against another, leading to misaccounting.
Fix this by just removing the repick code in smb2_async_writev(). As this
is only called from netfslib-driven code, cifs_prepare_write() should
always have been called first, and so server should never be NULL and the
preparatory step is repeated in the event that we do a retry.
The problem manifests as a warning looking something like:
WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs]
...
RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs]
...
smb2_writev_callback+0x334/0x560 [cifs]
cifs_demultiplex_thread+0x77a/0x11b0 [cifs]
kthread+0x187/0x1d0
ret_from_fork+0x34/0x60
ret_from_fork_asm+0x1a/0x30
Which may be triggered by a number of different xfstests running against an
Azure server in multichannel mode. generic/249 seems the most repeatable,
but generic/215, generic/249 and generic/308 may also show it.
Fixes: 3ee1a1fc3981 ("cifs: Cut over to using netfslib")
Reported-by: Steve French <sfrench@xxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Reviewed-by: Paulo Alcantara (Red Hat) <pc@xxxxxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: Aurelien Aptel <aaptel@xxxxxxxx>
cc: linux-cifs@xxxxxxxxxxxxxxx
cc: netfs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
fs/smb/client/smb2pdu.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index 2ae2dbb6202b..bb84a89e5905 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -4859,9 +4859,6 @@ smb2_async_writev(struct cifs_io_subrequest *wdata)
struct cifs_io_parms *io_parms = NULL;
int credit_request;
- if (!wdata->server || test_bit(NETFS_SREQ_RETRYING, &wdata->subreq.flags))
- server = wdata->server = cifs_pick_channel(tcon->ses);
-
/*
* in future we may get cifs_io_parms passed in from the caller,
* but for now we construct it here...
