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From: NeilBrown <>
To: Linux NFS Mailing List <>
Subject: NFSv4.1 backchannel xprt problems.
Date: Wed, 09 Oct 2019 16:15:04 +1100
Message-ID: <> (raw)

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 I have a customer with a 4.12-based kernel who is experiencing memory

 There are over 100,000 rpc_rqst structures queue on sv_cb_list for
 handing by the NFSv4 callback, which is idle.

 The rpc_rqst.rq_xprt pointer points to freed memory.

 I notice that that server code calls svc_xprt_get() on the xprt
 before storing it in rq_xprt, but the client/backchannel code doesn't.

 I'm wondering if the following might be useful.

 I plan to explore the code a bit more tomorrow and if this  still seems
 likely I get the customer to test this change, but I thought I would
 ask here as well incase someone more knowledgeable can give me any


diff --git a/net/sunrpc/backchannel_rqst.c b/net/sunrpc/backchannel_rqst.c
index 339e8c077c2d..c95ca39688b6 100644
--- a/net/sunrpc/backchannel_rqst.c
+++ b/net/sunrpc/backchannel_rqst.c
@@ -61,6 +61,7 @@ static void xprt_free_allocation(struct rpc_rqst *req)
 	free_page((unsigned long)xbufp->head[0].iov_base);
 	xbufp = &req->rq_snd_buf;
 	free_page((unsigned long)xbufp->head[0].iov_base);
+	xprt_put(req->rq_xprt);
@@ -85,7 +86,7 @@ struct rpc_rqst *xprt_alloc_bc_req(struct rpc_xprt *xprt, gfp_t gfp_flags)
 	if (req == NULL)
 		return NULL;
-	req->rq_xprt = xprt;
+	req->rq_xprt = xprt_get(xprt);
 	/* Preallocate one XDR receive buffer */

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             reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09  5:15 NeilBrown [this message]
2019-10-11 16:56 ` bfields
2019-10-14 23:36   ` [PATCH] SUNRPC: backchannel RPC request must reference XPRT NeilBrown
2019-10-15 21:16     ` Trond Myklebust
2019-10-15 21:47       ` Chuck Lever
2019-10-15 23:23       ` NeilBrown
2019-10-16  3:04         ` Trond Myklebust
2019-10-16  4:38           ` NeilBrown

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