linux-kernel - [PATCH] smp: Do not warn if smp_call_function

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Date:   Fri, 12 Apr 2019 23:53:57 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "riel@...riel.com" <riel@...riel.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "luto@...nel.org" <luto@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>
CC:     "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "apw@...onical.com" <apw@...onical.com>,
        "olaf@...fle.de" <olaf@...fle.de>, vkuznets <vkuznets@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        Dexuan Cui <decui@...rosoft.com>
Subject: [PATCH] smp: Do not warn if smp_call_function_single() is doing a
 self call.

If smp_call_function_single() is calling the function for itself, it's safe
to run with irqs_disabled() == true.

I hit the warning because I'm in the below path in the .suspend callback of
a "syscore_ops" to support hibernation for a VM running on Hyper-V:

  hv_synic_cleanup() ->
    clockevents_unbind_device() ->
      clockevents_unbind() ->
        smp_call_function_single().

When the .suspend callback runs, only CPU0 is online and irqs_disabled() is
true.

Signed-off-by: Dexuan Cui <decui@...rosoft.com>
---
 kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index f4cf1b0bb3b8..4fdf6a378def 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -288,7 +288,7 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
 	 * can't happen.
 	 */
 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
-		     && !oops_in_progress);
+		     && cpu != smp_processor_id() && !oops_in_progress);
 
 	csd = &csd_stack;
 	if (!wait) {
-- 
2.19.1