From: Akinobu Mita <akinobu.mita@gmail.com>
Date: Sat, 26 Sep 2015 17:09:19 +0000 (+0900)
Subject: blk-mq: avoid setting hctx->tags->cpumask before allocation
X-Git-Tag: v4.2.4~5
X-Git-Url: http://git.hungrycats.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5781175fab1a2c8b0339644fb27d64bf24c9fda4;p=linux

blk-mq: avoid setting hctx->tags->cpumask before allocation

commit 1356aae08338f1c19ce1c67bf8c543a267688fc3 upstream.

When unmapped hw queue is remapped after CPU topology is changed,
hctx->tags->cpumask has to be set after hctx->tags is setup in
blk_mq_map_swqueue(), otherwise it causes null pointer dereference.

Fixes: f26cdc8536 ("blk-mq: Shared tag enhancements")
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 176262ec3731..c69902695136 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1807,7 +1807,6 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 
 		hctx = q->mq_ops->map_queue(q, i);
 		cpumask_set_cpu(i, hctx->cpumask);
-		cpumask_set_cpu(i, hctx->tags->cpumask);
 		ctx->index_hw = hctx->nr_ctx;
 		hctx->ctxs[hctx->nr_ctx++] = ctx;
 	}
@@ -1847,6 +1846,14 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 		hctx->next_cpu = cpumask_first(hctx->cpumask);
 		hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
 	}
+
+	queue_for_each_ctx(q, ctx, i) {
+		if (!cpu_online(i))
+			continue;
+
+		hctx = q->mq_ops->map_queue(q, i);
+		cpumask_set_cpu(i, hctx->tags->cpumask);
+	}
 }
 
 static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set)