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: Michael Tokarev <mjt@tls.msk.ru> Tested-by: Michael Tokarev <mjt@tls.msk.ru> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
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@ -316,7 +316,6 @@ static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt)
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*/
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void svc_xprt_enqueue(struct svc_xprt *xprt)
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{
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struct svc_serv *serv = xprt->xpt_server;
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struct svc_pool *pool;
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struct svc_rqst *rqstp;
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int cpu;
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@ -362,8 +361,6 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)
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rqstp, rqstp->rq_xprt);
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rqstp->rq_xprt = xprt;
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svc_xprt_get(xprt);
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rqstp->rq_reserved = serv->sv_max_mesg;
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atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
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pool->sp_stats.threads_woken++;
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wake_up(&rqstp->rq_wait);
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} else {
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@ -640,8 +637,6 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
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if (xprt) {
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rqstp->rq_xprt = xprt;
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svc_xprt_get(xprt);
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rqstp->rq_reserved = serv->sv_max_mesg;
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atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
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/* As there is a shortage of threads and this request
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* had to be queued, don't allow the thread to wait so
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@ -738,6 +733,8 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
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else
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len = xprt->xpt_ops->xpo_recvfrom(rqstp);
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dprintk("svc: got len=%d\n", len);
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rqstp->rq_reserved = serv->sv_max_mesg;
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atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
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}
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svc_xprt_received(xprt);
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