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

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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 e027fffff7 ("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: 2f75d9e1c9 ("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
This commit is contained in:
Thomas Gleixner 2020-08-30 19:07:53 +02:00
parent e027fffff7
commit 784a083037
1 changed files with 7 additions and 0 deletions
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7
kernel/irq/matrix.c
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@ -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;