[PATCH net] mctp: perform route destruction under RCU read lock

The kernel test robot reports:

  [  843.509974][  T345] =============================
  [  843.524220][  T345] WARNING: suspicious RCU usage
  [  843.538791][  T345] 5.14.0-rc2-00606-g889b7da23abf #1 Not tainted
  [  843.553617][  T345] -----------------------------
  [  843.567412][  T345] net/mctp/route.c:310 RCU-list traversed in non-reader section!!

- we're missing the rcu read lock acquire around the destruction path.

This change adds the acquire/release - the path is already atomic, and
we're using the _rcu list iterators.

Reported-by: kernel test robot <redacted>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
---
 net/mctp/route.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mctp/route.c b/net/mctp/route.c
index 5265525011ad..5ca186d53cb0 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c

@@ -1083,8 +1083,10 @@ static void __net_exit mctp_routes_net_exit(struct net *net)
 {
 	struct mctp_route *rt;
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(rt, &net->mctp.routes, list)
 		mctp_route_release(rt);
+	rcu_read_unlock();
 }
 
 static struct pernet_operations mctp_net_ops = {

-- 
2.30.2

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Wed,  8 Sep 2021 12:13:10 +0800 you wrote:

The kernel test robot reports:

  [  843.509974][  T345] =============================
  [  843.524220][  T345] WARNING: suspicious RCU usage
  [  843.538791][  T345] 5.14.0-rc2-00606-g889b7da23abf #1 Not tainted
  [  843.553617][  T345] -----------------------------
  [  843.567412][  T345] net/mctp/route.c:310 RCU-list traversed in non-reader section!!

[...]

Here is the summary with links:
  - [net] mctp: perform route destruction under RCU read lock
    https://git.kernel.org/netdev/net/c/581edcd0c8a0

You are awesome, thank you!
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