[GIT pull] irq fix for 4.15

[Thomas Gleixner <tglx@linutronix.de>]

Linus,

please pull the latest irq-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git irq-urgent-for-linus

A single fix for the new matrix allocator to prevent vector exhaustion by
certain network drivers which allocate gazillions of unused vectors which
cannot be put into reservation mode due to MSI and the lack of MSI entry
masking. The fix/workaround is to spread the vectors across CPUs by
searching the supplied target CPU mask for the CPU with the smallest number
of allocated vectors.

Thanks,

	tglx

------------------>
Thomas Gleixner (1):
      irq/matrix: Spread interrupts on allocation


 kernel/irq/matrix.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
index 0ba0dd8863a7..5187dfe809ac 100644
--- a/kernel/irq/matrix.c
+++ b/kernel/irq/matrix.c
@@ -321,15 +321,23 @@ void irq_matrix_remove_reserved(struct irq_matrix *m)
 int irq_matrix_alloc(struct irq_matrix *m, const struct cpumask *msk,
 		     bool reserved, unsigned int *mapped_cpu)
 {
-	unsigned int cpu;
+	unsigned int cpu, best_cpu, maxavl = 0;
+	struct cpumap *cm;
+	unsigned int bit;
 
+	best_cpu = UINT_MAX;
 	for_each_cpu(cpu, msk) {
-		struct cpumap *cm = per_cpu_ptr(m->maps, cpu);
-		unsigned int bit;
+		cm = per_cpu_ptr(m->maps, cpu);
 
-		if (!cm->online)
+		if (!cm->online || cm->available <= maxavl)
 			continue;
 
+		best_cpu = cpu;
+		maxavl = cm->available;
+	}
+
+	if (maxavl) {
+		cm = per_cpu_ptr(m->maps, best_cpu);
 		bit = matrix_alloc_area(m, cm, 1, false);
 		if (bit < m->alloc_end) {
 			cm->allocated++;
@@ -338,8 +346,8 @@ int irq_matrix_alloc(struct irq_matrix *m, const struct cpumask *msk,
 			m->global_available--;
 			if (reserved)
 				m->global_reserved--;
-			*mapped_cpu = cpu;
-			trace_irq_matrix_alloc(bit, cpu, m, cm);
+			*mapped_cpu = best_cpu;
+			trace_irq_matrix_alloc(bit, best_cpu, m, cm);
 			return bit;
 		}
 	}