smp: Process pending softirqs in flush_smp_call_function_from_idle()

send_call_function_single_ipi() may wake an idle CPU without sending an
IPI. The woken up CPU will process the SMP-functions in
flush_smp_call_function_from_idle(). Any raised softirq from within the
SMP-function call will not be processed.
Should the CPU have no tasks assigned, then it will go back to idle with
pending softirqs and the NOHZ will rightfully complain.

Process pending softirqs on return from flush_smp_call_function_queue().

Fixes: b2a02fc43a1f4 ("smp: Optimize send_call_function_single_ipi()")
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210123201027.3262800-2-bigeasy@linutronix.de

diff --git a/kernel/smp.c b/kernel/smp.c
index 1b6070bf97bb01f76cea0a7a51bee0c59f3c15ec..aeb0adfa060637fbbef23bebcf15e26c93bd046e 100644 (file)
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -14,6 +14,7 @@
 #include <linux/export.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
+#include <linux/interrupt.h>
 #include <linux/gfp.h>
 #include <linux/smp.h>
 #include <linux/cpu.h>
@@ -449,6 +450,9 @@ void flush_smp_call_function_from_idle(void)
 
        local_irq_save(flags);
        flush_smp_call_function_queue(true);
+       if (local_softirq_pending())
+               do_softirq();
+
        local_irq_restore(flags);
 }