From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 29 Jan 2015 15:10:08 +0100
Subject: block/mq: don't complete requests via IPI
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.3-rt1.tar.xz

The IPI runs in hardirq context and there are sleeping locks. Assume caches are
shared and complete them on the local CPU.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 block/blk-mq.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -612,8 +612,16 @@ static void __blk_mq_complete_request(st
 	}
 
 	cpu = get_cpu_light();
+	/*
+	 * Avoid SMP function calls for completions because they acquire
+	 * sleeping spinlocks on RT.
+	 */
+#ifdef CONFIG_PREEMPT_RT
+	shared = true;
+#else
 	if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 		shared = cpus_share_cache(cpu, ctx->cpu);
+#endif
 
 	if (cpu != ctx->cpu && !shared && cpu_online(ctx->cpu)) {
 		rq->csd.func = __blk_mq_complete_request_remote;