Commit 05258a0a authored by Chuck Lever's avatar Chuck Lever
Browse files

SUNRPC: Fix a slow server-side memory leak with RPC-over-TCP 



Jan Schunk reports that his small NFS servers suffer from memory
exhaustion after just a few days. A bisect shows that commit
e18e157b ("SUNRPC: Send RPC message on TCP with a single
sock_sendmsg() call") is the first bad commit.

That commit assumed that sock_sendmsg() releases all the pages in
the underlying bio_vec array, but the reality is that it doesn't.
svc_xprt_release() releases the rqst's response pages, but the
record marker page fragment isn't one of those, so it is never
released.

This is a narrow fix that can be applied to stable kernels. A
more extensive fix is in the works.

Reported-by: default avatarJan Schunk <scpcom@gmx.de>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218671


Fixes: e18e157b ("SUNRPC: Send RPC message on TCP with a single sock_sendmsg() call")
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Reviewed-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
parent 99dc2ef0

net/sunrpc/svcsock.c

+1 −9
Original line number Diff line number Diff line
@@ -1206,15 +1206,6 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp) 
 * MSG_SPLICE_PAGES is used exclusively to reduce the number of

 * copy operations in this path. Therefore the caller must ensure

 * that the pages backing @xdr are unchanging.

 *

 * Note that the send is non-blocking. The caller has incremented

 * the reference count on each page backing the RPC message, and

 * the network layer will "put" these pages when transmission is

 * complete.

 *

 * This is safe for our RPC services because the memory backing

 * the head and tail components is never kmalloc'd. These always

 * come from pages in the svc_rqst::rq_pages array.

 */

static int svc_tcp_sendmsg(struct svc_sock *svsk, struct svc_rqst *rqstp,

			   rpc_fraghdr marker, unsigned int *sentp)
@@ -1244,6 +1235,7 @@ static int svc_tcp_sendmsg(struct svc_sock *svsk, struct svc_rqst *rqstp, 
	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec,

		      1 + count, sizeof(marker) + rqstp->rq_res.len);

	ret = sock_sendmsg(svsk->sk_sock, &msg);

	page_frag_free(buf);

	if (ret < 0)

		return ret;

	*sentp += ret;