Patch "pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised" has been added to the 4.7-stable tree

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 4.7-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-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Trond Myklebust <[email protected]>
Date: Sat, 3 Sep 2016 10:39:51 -0400
Subject: pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised

From: Trond Myklebust <[email protected]>

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).

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

@@ -876,6 +876,9 @@ void pnfs_clear_layoutreturn_waitbit(str
 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 [email protected] are

queue-4.7/nfsv4.1-fix-oopsable-condition-in-server-callback-races.patch queue-4.7/pnfs-ensure-layoutget-and-layoutreturn-are-properly-serialised.patch queue-4.7/nfsv4.x-fix-a-refcount-leak-in-nfs_callback_up_net.patch queue-4.7/pnfs-flexfiles-fix-an-oopsable-condition-when-connection-to-the-ds-fails.patch queue-4.7/nfsv4.1-fix-the-create_session-slot-number-accounting.patch queue-4.7/pnfs-the-client-must-not-do-i-o-to-the-ds-if-it-s-lease-has-expired.patch