linux-kernel - [PATCH 3.16 091/136] NFS: Avoid RCU usage in tracepoints

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Date:   Sun, 11 Feb 2018 04:31:11 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Dave Jones" <davej@...emonkey.org.uk>,
        "Anna Schumaker" <Anna.Schumaker@...app.com>
Subject: [PATCH 3.16 091/136] NFS: Avoid RCU usage in tracepoints

3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Anna Schumaker <Anna.Schumaker@...app.com>

commit 3944369db701f075092357b511fd9f5755771585 upstream.

There isn't an obvious way to acquire and release the RCU lock during a
tracepoint, so we can't use the rpc_peeraddr2str() function here.
Instead, rely on the client's cl_hostname, which should have similar
enough information without needing an rcu_dereference().

Reported-by: Dave Jones <davej@...emonkey.org.uk>
Signed-off-by: Anna Schumaker <Anna.Schumaker@...app.com>
[bwh: Backported to 3.16: Drop changes in
 nfs4_inode{,_stateid}_callback_event()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/nfs/nfs4trace.h | 24 ++++++------------------
 1 file changed, 6 insertions(+), 18 deletions(-)

--- a/fs/nfs/nfs4trace.h
+++ b/fs/nfs/nfs4trace.h
@@ -201,17 +201,13 @@ DECLARE_EVENT_CLASS(nfs4_clientid_event,
 		TP_ARGS(clp, error),
 
 		TP_STRUCT__entry(
-			__string(dstaddr,
-				rpc_peeraddr2str(clp->cl_rpcclient,
-					RPC_DISPLAY_ADDR))
+			__string(dstaddr, clp->cl_hostname)
 			__field(int, error)
 		),
 
 		TP_fast_assign(
 			__entry->error = error;
-			__assign_str(dstaddr,
-				rpc_peeraddr2str(clp->cl_rpcclient,
-						RPC_DISPLAY_ADDR));
+			__assign_str(dstaddr, clp->cl_hostname);
 		),
 
 		TP_printk(