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Commit d10f27a7 authored by J. Bruce Fields's avatar J. Bruce Fields
Browse files

svcrpc: fix svc_xprt_enqueue/svc_recv busy-looping 



The rpc server tries to ensure that there will be room to send a reply
before it receives a request.

It does this by tracking, in xpt_reserved, an upper bound on the total
size of the replies that is has already committed to for the socket.

Currently it is adding in the estimate for a new reply *before* it
checks whether there is space available.  If it finds that there is not
space, it then subtracts the estimate back out.

This may lead the subsequent svc_xprt_enqueue to decide that there is
space after all.

The results is a svc_recv() that will repeatedly return -EAGAIN, causing
server threads to loop without doing any actual work.

Cc: stable@vger.kernel.org
Reported-by: default avatarMichael Tokarev <mjt@tls.msk.ru>
Tested-by: default avatarMichael Tokarev <mjt@tls.msk.ru>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent f06f00a2

net/sunrpc/svc_xprt.c

+2 −5
Original line number Diff line number Diff line
@@ -316,7 +316,6 @@ static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt) 
 */

void svc_xprt_enqueue(struct svc_xprt *xprt)

{

	struct svc_serv	*serv = xprt->xpt_server;

	struct svc_pool *pool;

	struct svc_rqst	*rqstp;

	int cpu;
@@ -362,8 +361,6 @@ void svc_xprt_enqueue(struct svc_xprt *xprt) 
				rqstp, rqstp->rq_xprt);

		rqstp->rq_xprt = xprt;

		svc_xprt_get(xprt);

		rqstp->rq_reserved = serv->sv_max_mesg;

		atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);

		pool->sp_stats.threads_woken++;

		wake_up(&rqstp->rq_wait);

	} else {
@@ -640,8 +637,6 @@ int svc_recv(struct svc_rqst *rqstp, long timeout) 
	if (xprt) {

		rqstp->rq_xprt = xprt;

		svc_xprt_get(xprt);

		rqstp->rq_reserved = serv->sv_max_mesg;

		atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);



		/* As there is a shortage of threads and this request

		 * had to be queued, don't allow the thread to wait so
@@ -738,6 +733,8 @@ int svc_recv(struct svc_rqst *rqstp, long timeout) 
		else

			len = xprt->xpt_ops->xpo_recvfrom(rqstp);

		dprintk("svc: got len=%d\n", len);

		rqstp->rq_reserved = serv->sv_max_mesg;

		atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);

	}

	svc_xprt_received(xprt);