Re: [PATCH 4.21 V3] blk-mq: not embed .mq_kobj and ctx->kobj into queue instance

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Nov 20, 2018 at 09:44:35AM +0800, Ming Lei wrote:
> 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>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> V3:
> 	- keep to allocate q->queue_ctx via percpu allocator, so one extra
> 	  pointer reference can be saved for getting ctx
> V2:
> 	- allocate 'blk_mq_ctx' inside blk_mq_init_allocated_queue()
> 	- allocate q->mq_kobj directly 

Not tested, but seems sane from a kobject point-of-view:

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>