smp_call_function_many: handle concurrent clearing of mask (723aae25) · Commits · 戴 / test

Mike Galbraith reported finding a lockup ("perma-spin bug") where the cpumask passed to smp_call_function_many was cleared by other cpu(s) while a cpu was preparing its call_data block, resulting in no cpu to clear the last ref and unlock the block. Having cpus clear their bit asynchronously could be useful on a mask of cpus that might have a translation context, or cpus that need a push to complete an rcu window. Instead of adding a BUG_ON and requiring yet another cpumask copy, just detect the race and handle it. Note: arch_send_call_function_ipi_mask must still handle an empty cpumask because the data block is globally visible before the that arch callback is made. And (obviously) there are no guarantees to which cpus are notified if the mask is changed during the call; only cpus that were online and had their mask bit set during the whole call are guaranteed to be called. Reported-by:

Mike Galbraith <efault@gmx.de> Reported-by:

Jan Beulich <JBeulich@novell.com> Acked-by:

Jan Beulich <jbeulich@novell.com> Cc: stable@kernel.org Signed-off-by:

Milton Miller <miltonm@bga.com> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/smp.c

+10 −3

Original line number	Diff line number	Diff line
		@@ -450,7 +450,7 @@ void smp_call_function_many(const struct cpumask *mask,
		{
		struct call_function_data *data;
		unsigned long flags;
		int cpu, next_cpu, this_cpu = smp_processor_id();
		int refs, cpu, next_cpu, this_cpu = smp_processor_id();

		/*
		* Can deadlock when called with interrupts disabled.
		@@ -461,7 +461,7 @@ void smp_call_function_many(const struct cpumask *mask,
		WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
		&& !oops_in_progress && !early_boot_irqs_disabled);

		/* So, what's a CPU they want? Ignoring this one. */
		/* Try to fastpath. So, what's a CPU they want? Ignoring this one. */
		cpu = cpumask_first_and(mask, cpu_online_mask);
		if (cpu == this_cpu)
		cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
		@@ -519,6 +519,13 @@ void smp_call_function_many(const struct cpumask *mask,
		/* We rely on the "and" being processed before the store */
		cpumask_and(data->cpumask, mask, cpu_online_mask);
		cpumask_clear_cpu(this_cpu, data->cpumask);
		refs = cpumask_weight(data->cpumask);

		/* Some callers race with other cpus changing the passed mask */
		if (unlikely(!refs)) {
		csd_unlock(&data->csd);
		return;
		}

		raw_spin_lock_irqsave(&call_function.lock, flags);
		/*
		@@ -532,7 +539,7 @@ void smp_call_function_many(const struct cpumask *mask,
		* to the cpumask before this write to refs, which indicates
		* data is on the list and is ready to be processed.
		*/
		atomic_set(&data->refs, cpumask_weight(data->cpumask));
		atomic_set(&data->refs, refs);
		raw_spin_unlock_irqrestore(&call_function.lock, flags);

		/*

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