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

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Jan Schunk reports that his small NFS servers suffer from memory
exhaustion after just a few days. A bisect shows that commit
e18e157bb5 ("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: Jan Schunk <scpcom@gmx.de>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218671
Fixes: e18e157bb5 ("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: David Howells <dhowells@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Chuck Lever 2024-04-03 10:36:25 -04:00
parent 99dc2ef039
commit 05258a0a69
1 changed files with 1 additions and 9 deletions
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10
net/sunrpc/svcsock.c
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@ -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;