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>
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 0d693a8..bac973a 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -316,7 +316,6 @@
*/
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 @@
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 @@
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 @@
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);