[1/3] smp: Process pending softirqs in flush_smp_call_function_from_idle()
diff mbox series

Message ID 20210123201027.3262800-2-bigeasy@linutronix.de
State New, archived
Headers show
Series
  • blk-mq: Don't complete in IRQ, use llist_head
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Commit Message

Sebastian Andrzej Siewior Jan. 23, 2021, 8:10 p.m. UTC
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>
---
 kernel/smp.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Sebastian Andrzej Siewior Feb. 1, 2021, 7:35 p.m. UTC | #1
On 2021-01-23 21:10:25 [+0100], To linux-block@vger.kernel.org wrote:
> 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>

A gentle ping.
This isn't just a requirement for the series: rps_trigger_softirq() is
invoked from smp_call_function_single_async() and raises a softirq.

Sebastian
Peter Zijlstra Feb. 9, 2021, 10:02 a.m. UTC | #2
On Sat, Jan 23, 2021 at 09:10:25PM +0100, Sebastian Andrzej Siewior wrote:
> 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>

Fair enough. I'll stick this in tip/sched/smp for Jens and merge that
into tip/sched/core.

Thanks!
Sebastian Andrzej Siewior Feb. 9, 2021, 11:35 a.m. UTC | #3
On 2021-02-09 11:02:10 [+0100], Peter Zijlstra wrote:
> Fair enough. I'll stick this in tip/sched/smp for Jens and merge that
> into tip/sched/core.

Thank you.

> Thanks!

Sebastian

Patch
diff mbox series

diff --git a/kernel/smp.c b/kernel/smp.c
index 1b6070bf97bb0..aeb0adfa06063 100644
--- 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);
 }