Re: [PATCH] mpls: Add missing RCU-bh read side critical section locking in output path

On 20/06/16 19:05, Lennert Buytenhek wrote:

From: David Barroso <redacted>

When locally originated IP traffic hits a route that says to push
MPLS labels, we'll get a call chain dst_output() -> lwtunnel_output()
-> mpls_output() -> neigh_xmit() -> ___neigh_lookup_noref() where the
last function in this chain accesses a RCU-bh protected struct
neigh_table pointer without us ever having declared an RCU-bh read
side critical section.

As in case of locally originated IP traffic we'll be running in process
context, with softirqs enabled, we can be preempted by a softirq at any
time, and RCU-bh considers the completion of a softirq as signaling
the end of any pending read-side critical sections, so if we do get a
softirq here, we can end up with an unexpected RCU grace period and
all the nastiness that that comes with.

This patch makes neigh_xmit() take rcu_read_{,un}lock_bh() around the
code that expects to be treated as an RCU-bh read side critical section.

Signed-off-by: David Barroso <redacted>
Signed-off-by: Lennert Buytenhek <redacted>

LGTM too.

Acked-by: Robert Shearman <redacted>