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sunrpc: Remove backchannel check in svc_init_buffer()

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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.

This approach avoids introducing extra conditional logic in
svc_alloc_args(), which is a hot path.

Acked-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Chuck Lever 2025-04-28 15:36:51 -04:00
parent eff042ddf4
commit 1a58791292
1 changed files with 0 additions and 4 deletions
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4
net/sunrpc/svc.c
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@ -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
*/