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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>
This commit is contained in:
J. Bruce Fields 2012-08-17 17:31:53 -04:00
parent f06f00a24d
commit d10f27a750
1 changed files with 2 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
net/sunrpc/svc_xprt.c
View File

@ -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);