From 3ba10f9a6ae3c1b339fb7ff78a6bc9c314e3e08c Mon Sep 17 00:00:00 2001
From: Ryan Moeller <ryan@iXsystems.com>
Date: Mon, 29 Mar 2021 15:44:27 -0400
Subject: [PATCH] Atomically check and set dropped zevent count

ratelimit_dropped isn't protected by a lock and is expected to
be updated atomically.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #11822
---
 module/zfs/fm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/module/zfs/fm.c b/module/zfs/fm.c
index 3070cab1e4..c79d291ab1 100644
--- a/module/zfs/fm.c
+++ b/module/zfs/fm.c
@@ -657,8 +657,7 @@ zfs_zevent_next(zfs_zevent_t *ze, nvlist_t **event, uint64_t *event_size,
 
 #ifdef _KERNEL
 	/* Include events dropped due to rate limiting */
-	*dropped += ratelimit_dropped;
-	ratelimit_dropped = 0;
+	*dropped += atomic_swap_64(&ratelimit_dropped, 0);
 #endif
 	ze->ze_dropped = 0;
 out: