Patch "blk-mq: avoid setting hctx->tags->cpumask before allocation" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
blk-mq-avoid-setting-hctx-tags-cpumask-before-allocation.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Akinobu Mita <[email protected]>
Date: Sun, 27 Sep 2015 02:09:19 +0900
Subject: blk-mq: avoid setting hctx->tags->cpumask before allocation

From: Akinobu Mita <[email protected]>

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.

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

@@ -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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/blk-mq-avoid-setting-hctx-tags-cpumask-before-allocation.patch