linux-kernel - Re: cpu stopper threads and load balancing leads to deadlock

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Date:   Thu, 3 May 2018 14:49:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mike Galbraith <efault@....de>
Cc:     Matt Fleming <matt@...eblueprint.co.uk>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: cpu stopper threads and load balancing leads to deadlock

On Thu, May 03, 2018 at 02:40:21PM +0200, Mike Galbraith wrote:
> On Thu, 2018-05-03 at 14:28 +0200, Peter Zijlstra wrote:
> > 
> > Hurm.. I don't see how this is 'new'. We moved the wakeup out from under
> > stopper lock, but that should not affect the RCU state.
> 
> No, not new, just an additional woes from same spot.

Ah, ok. Does somsething like this make it go away?


diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index f89014a2c238..a32518c2ba4a 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -650,8 +650,10 @@ int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
 	/* Schedule work on other CPUs and execute directly for local CPU */
 	set_state(&msdata, MULTI_STOP_PREPARE);
 	cpu_stop_init_done(&done, num_active_cpus());
-	queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
-			     &done);
+
+	RCU_NONIDLE(queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop,
+				         &msdata, &done));
+
 	ret = multi_cpu_stop(&msdata);
 
 	/* Busy wait for completion. */