[PATCH v3 01/11] sunrpc: Remove backchannel check in svc_init_buffer()

[cel@kernel.org]

From: Chuck Lever <chuck.lever@oracle.com>

The server's backchannel uses struct svc_rqst, but does not use the
pages in svc_rqst::rq_pages. It's rq_arg::pages and rq_res::pages
comes from the RPC client's page allocator. Currently,
svc_init_buffer() skips allocating pages in rq_pages for that
reason.

Except that, svc_rqst::rq_pages is filled anyway when a backchannel
svc_rqst is passed to svc_recv() -> and then to svc_alloc_arg().

This isn't really a problem at the moment, except that these pages
are allocated but then never used, as far as I can tell.

The problem is that later in this series, in addition to populating
the entries of rq_pages[], svc_init_buffer() will also allocate the
memory underlying the rq_pages[] array itself. If that allocation is
skipped, then svc_alloc_args() chases a NULL pointer for ingress
backchannel requests.

I'm not sure the way proposed here is best, but it does avoid
introducing extra conditional logic in svc_alloc_args(), which is a
hot path.

Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/svc.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index e7f9c295d13c..8ce3e6b3df6a 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -640,10 +640,6 @@ svc_init_buffer(struct svc_rqst *rqstp, unsigned int size, int node)
 {
 	unsigned long pages, ret;
 
-	/* bc_xprt uses fore channel allocated buffers */
-	if (svc_is_backchannel(rqstp))
-		return true;
-
 	pages = size / PAGE_SIZE + 1; /* extra page as we hold both request and reply.
 				       * We assume one is at most one page
 				       */
-- 
2.49.0