queue-3.16/padata-set-cpu_index-of-unused-cpus-to-1.patch

From: Mathias Krause <minipli@googlemail.com>
Date: Fri, 8 Sep 2017 20:57:09 +0200
Subject: padata: set cpu_index of unused CPUs to -1

commit 1bd845bcb41d5b7f83745e0cb99273eb376f2ec5 upstream.

The parallel queue per-cpu data structure gets initialized only for CPUs
in the 'pcpu' CPU mask set. This is not sufficient as the reorder timer
may run on a different CPU and might wrongly decide it's the target CPU
for the next reorder item as per-cpu memory gets memset(0) and we might
be waiting for the first CPU in cpumask.pcpu, i.e. cpu_index 0.

Make the '__this_cpu_read(pd->pqueue->cpu_index) == next_queue->cpu_index'
compare in padata_get_next() fail in this case by initializing the
cpu_index member of all per-cpu parallel queues. Use -1 for unused ones.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 kernel/padata.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -395,8 +395,14 @@ static void padata_init_pqueues(struct p
 	struct padata_parallel_queue *pqueue;
 
 	cpu_index = 0;
-	for_each_cpu(cpu, pd->cpumask.pcpu) {
+	for_each_possible_cpu(cpu) {
 		pqueue = per_cpu_ptr(pd->pqueue, cpu);
+
+		if (!cpumask_test_cpu(cpu, pd->cpumask.pcpu)) {
+			pqueue->cpu_index = -1;
+			continue;
+		}
+
 		pqueue->pd = pd;
 		pqueue->cpu_index = cpu_index;
 		cpu_index++;