stop_machine: Change cpu_stop_queue_two_works() to rely on stopper->enabled (d8bc8535) · Commits · 戴 / test

Change cpu_stop_queue_two_works() to ensure that both CPU's have stopper->enabled == T or fail otherwise. This way stop_two_cpus() no longer needs to check cpu_active() to avoid the deadlock. This patch doesn't remove these checks, we will do this later. Note: we need to take both stopper->lock's at the same time, but this will also help to remove lglock from stop_machine.c, so I hope this is fine. Signed-off-by:

Oleg Nesterov <oleg@redhat.com> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Tejun Heo <tj@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: heiko.carstens@de.ibm.com Link: http://lkml.kernel.org/r/20151008170141.GA25537@redhat.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/stop_machine.c

+20 −9

Original line number	Diff line number	Diff line
		@@ -219,12 +219,27 @@ static int multi_cpu_stop(void *data)
		static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
		int cpu2, struct cpu_stop_work *work2)
		{
		struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
		struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
		int err;

		lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
		cpu_stop_queue_work(cpu1, work1);
		cpu_stop_queue_work(cpu2, work2);
		spin_lock_irq(&stopper1->lock);
		spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);

		err = -ENOENT;
		if (!stopper1->enabled \|\| !stopper2->enabled)
		goto unlock;

		err = 0;
		__cpu_stop_queue_work(stopper1, work1);
		__cpu_stop_queue_work(stopper2, work2);
		unlock:
		spin_unlock(&stopper2->lock);
		spin_unlock_irq(&stopper1->lock);
		lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);

		return 0;
		return err;
		}
		/**
		* stop_two_cpus - stops two cpus
		@@ -261,12 +276,8 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
		set_state(&msdata, MULTI_STOP_PREPARE);

		/*
		* If we observe both CPUs active we know _cpu_down() cannot yet have
		* queued its stop_machine works and therefore ours will get executed
		* first. Or its not either one of our CPUs that's getting unplugged,
		* in which case we don't care.
		*
		* This relies on the stopper workqueues to be FIFO.
		* We do not want to migrate to inactive CPU. FIXME: move this
		* into migrate_swap_stop() callback.
		*/
		if (!cpu_active(cpu1) \|\| !cpu_active(cpu2)) {
		preempt_enable();

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