[PATCH 4.2 256/258] blk-mq: avoid setting hctx->tags->cpumask before allocation

[Greg Kroah-Hartman]

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Akinobu Mita <akinobu.mita@xxxxxxxxx>

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@xxxxxxxxx>
Cc: Keith Busch <keith.busch@xxxxxxxxx>
Cc: Ming Lei <tom.leiming@xxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 block/blk-mq.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1807,7 +1807,6 @@ static void blk_mq_map_swqueue(struct re
 
 		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 re
 		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)


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/