Commit d9eeca1e authored Aug 30, 2020 by Thomas Gleixner Committed by Greg Kroah-Hartman Sep 03, 2020

genirq/matrix: Deal with the sillyness of for_each_cpu() on UP



commit 784a0830377d0761834e385975bc46861fea9fa0 upstream.

Most of the CPU mask operations behave the same way, but for_each_cpu() and
it's variants ignore the cpumask argument and claim that CPU0 is always in
the mask. This is historical, inconsistent and annoying behaviour.

The matrix allocator uses for_each_cpu() and can be called on UP with an
empty cpumask. The calling code does not expect that this succeeds but
until commit e027fffff799 ("x86/irq: Unbreak interrupt affinity setting")
this went unnoticed. That commit added a WARN_ON() to catch cases which
move an interrupt from one vector to another on the same CPU. The warning
triggers on UP.

Add a check for the cpumask being empty to prevent this.

Fixes: 2f75d9e1 ("genirq: Implement bitmap matrix allocator")
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 9d57313c

kernel/irq/matrix.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -380,6 +380,13 @@ int irq_matrix_alloc(struct irq_matrix m, const struct cpumask msk,
		unsigned int cpu, bit;
		struct cpumap *cm;

		/*
		* Not required in theory, but matrix_find_best_cpu() uses
		* for_each_cpu() which ignores the cpumask on UP .
		*/
		if (cpumask_empty(msk))
		return -EINVAL;

		cpu = matrix_find_best_cpu(m, msk);
		if (cpu == UINT_MAX)
		return -ENOSPC;