svcrpc: fix svc_xprt_enqueue/svc_recv busy-looping (d10f27a7) · Commits · 戴 / test

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:

Michael Tokarev <mjt@tls.msk.ru> Tested-by:

Michael Tokarev <mjt@tls.msk.ru> Signed-off-by:

J. Bruce Fields <bfields@redhat.com>

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);

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