[PATCH] keys: use long workqueue for garbage collection

[Eduard Zateev <hackerowskiy@gmail.com>]

The key garbage collector can wait for RCU grace periods. This can occupy a
normal events worker for a long time and contribute to workqueue lockups.

Queue key GC on system_long_wq because its work may wait for long periods.

Reported-by: syzbot+c15de43f1e7fffbb7b9b@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=c15de43f1e7fffbb7b9b
Signed-off-by: Eduard Zateev <hackerowskiy@gmail.com>
---
 security/keys/gc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index eda445f815d..b174b8c511b 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -19,6 +19,7 @@ unsigned key_gc_delay = 5 * 60;
  * Reaper for unused keys.
  */
 static void key_garbage_collector(struct work_struct *work);
+/* Key GC may wait for RCU grace periods, so queue it on system_long_wq. */
 DECLARE_WORK(key_gc_work, key_garbage_collector);
 
 /*
@@ -57,7 +58,7 @@ void key_schedule_gc(time64_t gc_at)
 
 	if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) {
 		kdebug("IMMEDIATE");
-		schedule_work(&key_gc_work);
+		queue_work(system_long_wq, &key_gc_work);
 	} else if (gc_at < key_gc_next_run) {
 		kdebug("DEFERRED");
 		key_gc_next_run = gc_at;
@@ -85,7 +86,7 @@ void key_set_expiry(struct key *key, time64_t expiry)
 void key_schedule_gc_links(void)
 {
 	set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags);
-	schedule_work(&key_gc_work);
+	queue_work(system_long_wq, &key_gc_work);
 }
 
 /*
@@ -119,7 +120,7 @@ void key_gc_keytype(struct key_type *ktype)
 	set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);
 
 	kdebug("schedule");
-	schedule_work(&key_gc_work);
+	queue_work(system_long_wq, &key_gc_work);
 
 	kdebug("sleep");
 	wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE,
@@ -322,7 +323,7 @@ static void key_garbage_collector(struct work_struct *work)
 	}
 
 	if (gc_state & KEY_GC_REAP_AGAIN)
-		schedule_work(&key_gc_work);
+		queue_work(system_long_wq, &key_gc_work);
 	kleave(" [end %x]", gc_state);
 	return;
 
-- 
2.55.0