Re: [PATCH 12/13] loop: remove lo_refcount and avoid lo_mutex in ->open / ->release

[Jan Kara <jack@suse.cz>]

On Thu 24-03-22 18:47:01, Christoph Hellwig wrote:
> On Thu, Mar 24, 2022 at 06:15:18PM +0100, Christoph Hellwig wrote:
> > On Thu, Mar 24, 2022 at 03:13:21PM +0100, Jan Kara wrote:
> > > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > 
> > > Looks good but I still think we need something like attached preparatory
> > > patch to not regress e.g. filesystem probing triggered by udev events. What
> > > do you think?
> > 
> > Yes, I think it makes sense to add that.
> 
> Actually, looking at it in a little more detail: this misses the
> explicit kobject_uevent calls for the capacity changes.  I think the
> best idea might be something like this:
> 
> ---
> From db5ab8ab0fbcf07af769023a894fafc22b662cd9 Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Thu, 24 Mar 2022 18:41:28 +0100
> Subject: loop: suppress uevents while reconfiguring the device
> 
> Currently, udev change event is generated for a loop device before the
> device is ready for IO. Due to serialization on lo->lo_mutex in
> lo_open() this does not matter because anybody is able to open the
> device and do IO only after the configuration is finished. However this
> synchronization in lo_open() is going away so make sure userspace
> reacting to the change event will see the new device state by generating
> the event only when the device is setup.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Yeah, even better. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  drivers/block/loop.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index b3170e8cdbe95..bfd21af7aa38b 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -572,6 +572,10 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
>  
>  	if (!file)
>  		return -EBADF;
> +
> +	/* suppress uevents while reconfiguring the device */
> +	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);
> +
>  	is_loop = is_loop_device(file);
>  	error = loop_global_lock_killable(lo, is_loop);
>  	if (error)
> @@ -626,13 +630,18 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
>  	fput(old_file);
>  	if (partscan)
>  		loop_reread_partitions(lo);
> -	return 0;
> +
> +	error = 0;
> +done:
> +	/* enable and uncork uevent now that we are done */
> +	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
> +	return error;
>  
>  out_err:
>  	loop_global_unlock(lo, is_loop);
>  out_putf:
>  	fput(file);
> -	return error;
> +	goto done;
>  }
>  
>  /* loop sysfs attributes */
> @@ -999,6 +1008,9 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
>  	/* This is safe, since we have a reference from open(). */
>  	__module_get(THIS_MODULE);
>  
> +	/* suppress uevents while reconfiguring the device */
> +	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);
> +
>  	/*
>  	 * If we don't hold exclusive handle for the device, upgrade to it
>  	 * here to avoid changing device under exclusive owner.
> @@ -1101,7 +1113,12 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
>  		loop_reread_partitions(lo);
>  	if (!(mode & FMODE_EXCL))
>  		bd_abort_claiming(bdev, loop_configure);
> -	return 0;
> +
> +	error = 0;
> +done:
> +	/* enable and uncork uevent now that we are done */
> +	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
> +	return error;
>  
>  out_unlock:
>  	loop_global_unlock(lo, is_loop);
> @@ -1112,7 +1129,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
>  	fput(file);
>  	/* This is safe: open() is still holding a reference. */
>  	module_put(THIS_MODULE);
> -	return error;
> +	goto done;
>  }
>  
>  static void __loop_clr_fd(struct loop_device *lo, bool release)
> -- 
> 2.30.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR