Re: [PATCH] cifs: Fix oops due to uncleared server->smbd_conn in reconnect

From: David Howells <dhowells@redhat.com>
To: Tom Talpey <tom@talpey.com>
Cc: dhowells@redhat.com, Steve French <sfrench@samba.org>,
	Shyam Prasad N <nspmangalore@gmail.com>,
	Rohith Surabattula <rohiths.msft@gmail.com>,
	Long Li <longli@microsoft.com>,
	Namjae Jeon <linkinjeon@kernel.org>,
	Stefan Metzmacher <metze@samba.org>,
	Jeff Layton <jlayton@kernel.org>,
	linux-cifs@vger.kernel.org
Subject: Re: [PATCH] cifs: Fix oops due to uncleared server->smbd_conn in reconnect
Date: Wed, 25 Jan 2023 20:41:19 +0000	[thread overview]
Message-ID: <2302242.1674679279@warthog.procyon.org.uk> (raw)
In-Reply-To: <fa35788a-c858-11c5-5d9a-1d5c837020b6@talpey.com>

Hi Tom,

Steve suggested I should ask you about this.

I have IWarp RDMA mostly working with my iteratorisation patches - certainly
better than without them, but I think that's mostly due to the patch that
Stefan Metzmacher so dislikes ("cifs: Fix problem with encrypted RDMA data
read").

However, fallocate doesn't work:

   # rdma link add siw0 type siw netdev enp6s0 # andromeda, softIWarp
   # mount //192.168.6.1/test /xfstest.test -o user=shares,pass=foobar,rdma
   # fallocate -l 1M /xfstest.test/hello
   fallocate: fallocate failed: Resource temporarily unavailable

Because smb3_simple_fallocate_write_range() calls SMB2_write(), which calls
cifs_send_recv() then compound_send_recv() and thence to smb_send_rqst().

smb_send_rqst() encrypts the buffer it is given and smbd_send() attempts to
shovel it to the server using Direct Data Placement - which I think might fail
because the data is encrypted.

In one run of the above commands, the data in the kvec array looked like:

fe534d42400001000000000009000a0000000000000000001600000000000000a01300000200
0000000000000000000000000000000000000000000000000000000000000000000000000000

before the smb_send_rqst() gets to ->init_transform_rq() and like:

98eddc1bc31da7c55c00341e4dc769fa4c8b2b0ecdacbad33eb31855ec162fa2458b8437edc7
88ee0a033c84aa857b65ab31ce553594d412719cc3daf925e873e80062ec16b97c855721a42d

after.  The encrypted data is seen on the wire in DDP/RDMA packets.

Any thoughts as to how to fix this?

Does it need to pass a flag down to suppress the encryption or suppress the
use of direct data placement?  Or should it perhaps go through something like
->write_iter()?

Note also that it encrypts the buffer in place and then
smb3_simple_fallocate_write_range() reuses the buffer multiple times without
clearing it.

I've pushed my cifs iteratorisation patches to:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-cifs

I can post them by email a bit later.

David