| Date | Tue, 02 Oct 2012 00:54:08 +0200 | From | Willy Tarreau <> | Subject | [ 131/180] svcrpc: fix svc_xprt_enqueue/svc_recv busy-looping |
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2.6.32-longterm review patch. If anyone has any objections, please let me know.
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From: J. Bruce Fields <bfields@redhat.com>
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 <mjt@tls.msk.ru> Tested-by: Michael Tokarev <mjt@tls.msk.ru> Signed-off-by: J. Bruce Fields <bfields@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> --- net/sunrpc/svc_xprt.c | 7 ++----- 1 files changed, 2 insertions(+), 5 deletions(-)
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index 314320a..0ab2fed 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -304,7 +304,6 @@ 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; @@ -381,8 +380,6 @@ 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); rqstp->rq_waking = 1; pool->sp_nwaking++; pool->sp_stats.threads_woken++; @@ -667,8 +664,6 @@ 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); @@ -758,6 +753,8 @@ 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() */ -- 1.7.2.1.45.g54fbc
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