Commit 784a0830 authored by Thomas Gleixner's avatar Thomas Gleixner

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

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 e027ffff ("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: default avatarkernel test robot <>
Signed-off-by: default avatarThomas Gleixner <>
parent e027ffff
......@@ -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;
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