[1/4] pNFS: Ensure LAYOUTGET and LAYOUTRETURN are properly serialised
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Message ID 1473083162-4697-2-git-send-email-trond.myklebust@primarydata.com
State New
Headers show

Commit Message

Trond Myklebust Sept. 5, 2016, 1:45 p.m. UTC
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

Patch
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======					======
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>
Cc: stable@vger.kernel.org # v4.5+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
---
 fs/nfs/pnfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index 6daf034645c8..519ad320f5cd 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -899,6 +899,9 @@  pnfs_prepare_layoutreturn(struct pnfs_layout_hdr *lo,
 		nfs4_stateid *stateid,
 		enum pnfs_iomode *iomode)
 {
+	/* 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;
 	pnfs_get_layout_hdr(lo);