[PATCH v1 7/7] sunrpc: assign RQ_LOCAL from the transport on every receive

[Chuck Lever <cel@kernel.org>]

Only svc_tcp_recvfrom() assigns RQ_LOCAL. A request that arrives
over UDP or RDMA, or that svc_deferred_recv() replays, leaves the
svc_rqst with the value from the last TCP request its thread
received. When RQ_LOCAL is set, nfsd_vfs_write() sets
PF_LOCAL_THROTTLE, and dirty throttling considers only the backing
device being written. A stale RQ_LOCAL relaxes throttling that way
for a WRITE from a remote client. A stale clear bit withholds the
relaxation from a replayed WRITE that did arrive over loopback, and
NFSD can lock up behind the NFS client's dirty pages.

Assign RQ_LOCAL from XPT_LOCAL in svc_handle_xprt() before the
request is received. A deferred request is replayed on the
transport it arrived on, so struct svc_deferred_req needs no copy
of the flag. Only svc_tcp_accept() sets XPT_LOCAL. After the
change, RQ_LOCAL is clear for every UDP and RDMA request, including
one that arrives over loopback.

Fixes: ef11ce24875a ("SUNRPC: track whether a request is coming from a loop-back interface.")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 net/sunrpc/svc_xprt.c | 2 ++
 net/sunrpc/svcsock.c  | 2 --
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 031cbac2a612..acb6e58dc522 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -884,6 +884,8 @@ static void svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
 		svc_xprt_received(xprt);
 	} else if (svc_xprt_reserve_slot(rqstp, xprt)) {
 		/* XPT_DATA|XPT_DEFERRED case: */
+		assign_bit(RQ_LOCAL, &rqstp->rq_flags,
+			   test_bit(XPT_LOCAL, &xprt->xpt_flags));
 		rqstp->rq_deferred = svc_deferred_dequeue(xprt);
 		if (rqstp->rq_deferred)
 			len = svc_deferred_recv(rqstp);
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 1814e49c671d..b226bb3cd287 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1287,8 +1287,6 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
 
 	rqstp->rq_xprt_ctxt   = NULL;
 	rqstp->rq_prot	      = IPPROTO_TCP;
-	assign_bit(RQ_LOCAL, &rqstp->rq_flags,
-		   test_bit(XPT_LOCAL, &svsk->sk_xprt.xpt_flags));
 
 	/* Completing one message stops ->read_sock with whatever
 	 * follows still queued, and no path from here re-arms XPT_DATA.
-- 
2.55.0