From: J. Bruce Fields Date: Fri, 17 Aug 2012 21:31:53 +0000 (-0400) Subject: svcrpc: fix svc_xprt_enqueue/svc_recv busy-looping X-Git-Tag: v2.6.34.15~18 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2b718efa69f2431de9df4b35e725316fa25d5310;p=thirdparty%2Fkernel%2Fstable.git svcrpc: fix svc_xprt_enqueue/svc_recv busy-looping commit d10f27a750312ed5638c876e4bd6aa83664cccd8 upstream. 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. Reported-by: Michael Tokarev Tested-by: Michael Tokarev Signed-off-by: J. Bruce Fields Signed-off-by: Paul Gortmaker --- diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index 957a7e88e8273..afa0bceb67ad1 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -310,7 +310,6 @@ static void svc_thread_dequeue(struct svc_pool *pool, struct svc_rqst *rqstp) */ 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; @@ -384,8 +383,6 @@ 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++; BUG_ON(xprt->xpt_pool != pool); wake_up(&rqstp->rq_wait); @@ -663,8 +660,6 @@ 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); } else { /* No data pending. Go to sleep */ svc_thread_enqueue(pool, rqstp); @@ -754,6 +749,8 @@ 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); } /* No data, incomplete (TCP) read, or accept() */