Patch "pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pnfs-ensure-layoutget-and-layoutreturn-are-properly-serialised.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From bf0291dd2267a2b9a4cd74d65249553d11bb45d6 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <trond.myklebust@primarydata.com>
Date: Sat, 3 Sep 2016 10:39:51 -0400
Subject: pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised

From: Trond Myklebust <trond.myklebust@primarydata.com>

commit bf0291dd2267a2b9a4cd74d65249553d11bb45d6 upstream.

According to RFC5661, the client is responsible for serialising
LAYOUTGET and LAYOUTRETURN to avoid ambiguity. Consider the case
where we send both in parallel.

Client					Server
======					======
LAYOUTGET(seqid=X)
LAYOUTRETURN(seqid=X)
					LAYOUTGET return seqid=X+1
					LAYOUTRETURN return seqid=X+2
Process LAYOUTRETURN
          Forget layout stateid
Process LAYOUTGET
          Set seqid=X+1

The client processes the layoutget/layoutreturn in the wrong order,
and since the result of the layoutreturn was to clear the only
existing layout segment, the client forgets the layout stateid.

When the LAYOUTGET comes in, it is treated as having a completely
new stateid, and so the client sets the wrong sequence id...

Fix is to check if there are outstanding LAYOUTGET requests
before we send the LAYOUTRETURN (note that LAYOUGET will already
wait if it sees an outstanding LAYOUTRETURN).

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/nfs/pnfs.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -365,6 +365,9 @@ pnfs_layout_need_return(struct pnfs_layo
 static bool
 pnfs_prepare_layoutreturn(struct pnfs_layout_hdr *lo)
 {
+	/* Serialise LAYOUTGET/LAYOUTRETURN */
+	if (atomic_read(&lo->plh_outstanding) != 0)
+		return false;
 	if (test_and_set_bit(NFS_LAYOUT_RETURN, &lo->plh_flags))
 		return false;
 	lo->plh_return_iomode = 0;


Patches currently in stable-queue which might be from trond.myklebust@primarydata.com are

queue-4.4/nfsv4.1-fix-oopsable-condition-in-server-callback-races.patch
queue-4.4/pnfs-ensure-layoutget-and-layoutreturn-are-properly-serialised.patch
queue-4.4/nfsv4.x-fix-a-refcount-leak-in-nfs_callback_up_net.patch
queue-4.4/nfsv4.1-fix-the-create_session-slot-number-accounting.patch
queue-4.4/pnfs-the-client-must-not-do-i-o-to-the-ds-if-it-s-lease-has-expired.patch