releases/4.0.6/blk-mq-free-hctx-ctxs-in-queue-s-release-handler.patch

From c3b4afca7023b5aa0531912364246e67f79b3010 Mon Sep 17 00:00:00 2001
From: Ming Lei <tom.leiming@gmail.com>
Date: Thu, 4 Jun 2015 22:25:04 +0800
Subject: blk-mq: free hctx->ctxs in queue's release handler

From: Ming Lei <tom.leiming@gmail.com>

commit c3b4afca7023b5aa0531912364246e67f79b3010 upstream.

Now blk_cleanup_queue() can be called before calling
del_gendisk()[1], inside which hctx->ctxs is touched
from blk_mq_unregister_hctx(), but the variable has
been freed by blk_cleanup_queue() at that time.

So this patch moves freeing of hctx->ctxs into queue's
release handler for fixing the oops reported by Stefan.

[1], 6cd18e711dd8075 (block: destroy bdi before blockdev is
unregistered)

Reported-by: Stefan Seyfried <stefan.seyfried@googlemail.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 block/blk-mq.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1589,6 +1589,7 @@ static int blk_mq_hctx_notify(void *data
 	return NOTIFY_OK;
 }
 
+/* hctx->ctxs will be freed in queue's release handler */
 static void blk_mq_exit_hctx(struct request_queue *q,
 		struct blk_mq_tag_set *set,
 		struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
@@ -1607,7 +1608,6 @@ static void blk_mq_exit_hctx(struct requ
 
 	blk_mq_unregister_cpu_notifier(&hctx->cpu_notifier);
 	blk_free_flush_queue(hctx->fq);
-	kfree(hctx->ctxs);
 	blk_mq_free_bitmap(&hctx->ctx_map);
 }
 
@@ -1873,8 +1873,12 @@ void blk_mq_release(struct request_queue
 	unsigned int i;
 
 	/* hctx kobj stays in hctx */
-	queue_for_each_hw_ctx(q, hctx, i)
+	queue_for_each_hw_ctx(q, hctx, i) {
+		if (!hctx)
+			continue;
+		kfree(hctx->ctxs);
 		kfree(hctx);
+	}
 
 	kfree(q->queue_hw_ctx);