Re: [PATCH v3] block: genhd: don't call probe function with major_names_lock held

From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Hannes Reinecke <hare@suse.de>,
	Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>,
	Hillf Danton <hdanton@sina.com>,
	Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
	linux-block <linux-block@vger.kernel.org>
Subject: Re: [PATCH v3] block: genhd: don't call probe function with major_names_lock held
Date: Sun, 15 Aug 2021 16:49:55 +0900	[thread overview]
Message-ID: <a3f43d54-8d10-3272-1fbb-1193d9f1b6dd@i-love.sakura.ne.jp> (raw)
In-Reply-To: <YRi9EQJqfK6ldrZG@kroah.com>

On 2021/08/15 16:06, Greg KH wrote:
> On Sun, Aug 15, 2021 at 03:52:45PM +0900, Tetsuo Handa wrote:
>> --- a/include/linux/genhd.h
>> +++ b/include/linux/genhd.h
>> @@ -303,9 +303,9 @@ struct gendisk *__blk_alloc_disk(int node);
>>  void blk_cleanup_disk(struct gendisk *disk);
>>  
>>  int __register_blkdev(unsigned int major, const char *name,
>> -		void (*probe)(dev_t devt));
>> +		      void (*probe)(dev_t devt), struct module *owner);
>>  #define register_blkdev(major, name) \
>> -	__register_blkdev(major, name, NULL)
>> +	__register_blkdev(major, name, NULL, NULL)
>>  void unregister_blkdev(unsigned int major, const char *name);
> 
> Do not force modules to put their own THIS_MODULE macro as a parameter,
> put it in the .h file so that it happens automagically, much like the
> usb_register() define in include/linux/usb.h is created.

Sure. We can do like below.

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 13b34177cc85..70f00641fa11 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -302,10 +302,12 @@ extern void put_disk(struct gendisk *disk);
 struct gendisk *__blk_alloc_disk(int node);
 void blk_cleanup_disk(struct gendisk *disk);
 
-int __register_blkdev(unsigned int major, const char *name,
-		void (*probe)(dev_t devt));
+int ____register_blkdev(unsigned int major, const char *name,
+			void (*probe)(dev_t devt), struct module *owner);
+#define __register_blkdev(major, name, probe) \
+	____register_blkdev(major, name, probe, THIS_MODULE)
 #define register_blkdev(major, name) \
-	__register_blkdev(major, name, NULL)
+	____register_blkdev(major, name, NULL, NULL)
 void unregister_blkdev(unsigned int major, const char *name);
 
 bool bdev_check_media_change(struct block_device *bdev);

> 
> If you do that, you can probably get rid of the __register_blkdev()
> direct calls as well...

I assume "automagically" implies "do not patch individual unregister_blkdev() /
__register_blkdev() callers". But "removing __register_blkdev() direct calls"
requires "patching individual __register_blkdev() callers". I didn't catch
what you suggested here.

Anyway, since this patch should be backported to 5.11+ kernels, lines changed
should be kept minimal. We can do whatever remapping after this patch.
