[PATCH v1 2/5] SUNRPC: fire svc_defer_queue tracepoint before publishing the request

[Chuck Lever <cel@kernel.org>]

svc_revisit() adds the deferred request to xpt_deferred, drops
xpt_lock, and then fires trace_svc_defer_queue(), which reads the
request's XID and source address. Once the request is on the list,
an nfsd thread already servicing that transport can dequeue it in
svc_deferred_dequeue(), process it, and free it in
svc_xprt_release() before the tracepoint reads it. The window is
narrow, but nothing keeps the request alive across it.

Fire the tracepoint before the list_add(), while svc_revisit()
still owns the request.

Fixes: 8954c5c212d3 ("SUNRPC: Clean up request deferral tracepoints")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 net/sunrpc/svc_xprt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 908569035e57..713f4ba19ba1 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1271,9 +1271,9 @@ static void svc_revisit(struct cache_deferred_req *dreq, int too_many)
 		return;
 	}
 	dr->xprt = NULL;
+	trace_svc_defer_queue(dr);
 	list_add(&dr->handle.recent, &xprt->xpt_deferred);
 	spin_unlock(&xprt->xpt_lock);
-	trace_svc_defer_queue(dr);
 	svc_xprt_enqueue(xprt);
 	svc_xprt_put(xprt);
 }
-- 
2.55.0