blk-mq: not embed .mq_kobj and ctx->kobj into queue instance

Even though .mq_kobj, ctx->kobj and q->kobj share same lifetime
from block layer's view, actually they don't because userspace may
grab one kobject anytime via sysfs.

This patch fixes the issue by the following approach:

1) introduce 'struct blk_mq_ctxs' for holding .mq_kobj and managing
all ctxs

2) free all allocated ctxs and the 'blk_mq_ctxs' instance in release
handler of .mq_kobj

3) grab one ref of .mq_kobj before initializing each ctx->kobj, so that
.mq_kobj is always released after all ctxs are freed.

This patch fixes kernel panic issue during booting when DEBUG_KOBJECT_RELEASE
is enabled.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Cc: "jianchao.wang" <jianchao.w.wang@oracle.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 6 insertions, 0 deletions

diff --git a/block/blk-mq.h b/block/blk-mq.h
index facb6e9ddce4..9ae8e9f8f8b1 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -7,6 +7,11 @@
 
 struct blk_mq_tag_set;
 
+struct blk_mq_ctxs {
+	struct kobject kobj;
+	struct blk_mq_ctx __percpu	*queue_ctx;
+};
+
 /**
  * struct blk_mq_ctx - State for a software queue facing the submitting CPUs
  */
@@ -27,6 +32,7 @@ struct blk_mq_ctx {
 	unsigned long		____cacheline_aligned_in_smp rq_completed[2];
 
 	struct request_queue	*queue;
+	struct blk_mq_ctxs      *ctxs;
 	struct kobject		kobj;
 } ____cacheline_aligned_in_smp;