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 0e18aa336897 ("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: 19930038774a ("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

diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
index 30cc217b863184989987f2fa76c76c8bc9a082b4..651a4ad6d711f82d8192d07a6b7616ef9337651f 100644 (file)
--- a/kernel/irq/matrix.c
+++ b/kernel/irq/matrix.c
@@ -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;