[PATCH net-next v2 2/2] ipv6: mcast: annotate igmp6 timer expiry race

[Yuyang Huang]

/proc/net/igmp6 walks IPv6 multicast memberships under RCU and reads
mca_work.timer.expires to print the remaining multicast timer. The
delayed-work timer can be updated concurrently.

Annotate the intentional lockless procfs snapshot with READ_ONCE().

Signed-off-by: Yuyang Huang <sigefriedhyy@xxxxxxxxx>
---
 net/ipv6/mcast.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index bd3972730aa0..04b811b3be97 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -2984,6 +2984,7 @@ static int igmp6_mc_seq_show(struct seq_file *seq, void *v)
 	struct ifmcaddr6 *im = (struct ifmcaddr6 *)v;
 	struct igmp6_mc_iter_state *state = igmp6_mc_seq_private(seq);
 	unsigned int mca_flags = READ_ONCE(im->mca_flags);
+	unsigned long expires = READ_ONCE(im->mca_work.timer.expires);
 
 	seq_printf(seq,
 		   "%-4d %-15s %pi6 %5d %08X %ld\n",
@@ -2991,7 +2992,7 @@ static int igmp6_mc_seq_show(struct seq_file *seq, void *v)
 		   &im->mca_addr,
 		   READ_ONCE(im->mca_users), mca_flags,
 		   (mca_flags & MAF_TIMER_RUNNING) ?
-		   jiffies_to_clock_t(im->mca_work.timer.expires - jiffies) : 0);
+		   jiffies_to_clock_t(expires - jiffies) : 0);
 	return 0;
 }
 
-- 
2.43.0