Re: [PATCH v2] loop: properly send KOBJ_CHANGED uevent for disk device

[Greg KH]

On Tue, Apr 15, 2025 at 10:51:47AM +0200, Thomas Weißschuh wrote:
> The original commit message and the wording "uncork" in the code comment
> indicate that it is expected that the suppressed event instances are
> automatically sent after unsuppressing.
> This is not the case, instead they are discarded.
> In effect this means that no "changed" events are emitted on the device
> itself by default.
> While each discovered partition does trigger a changed event on the
> device, devices without partitions don't have any event emitted.
> 
> This makes udev miss the device creation and prompted workarounds in
> userspace. See the linked util-linux/losetup bug.
> 
> Explicitly emit the events and drop the confusingly worded comments.
> 
> Link: https://github.com/util-linux/util-linux/issues/2434
> Fixes: 498ef5c777d9 ("loop: suppress uevents while reconfiguring the device")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> ---
> Changes in v2:
> - Use correct Fixes tag
> - Rework commit message slightly
> - Rebase onto v6.15-rc1
> - Link to v1: https://lore.kernel.org/r/20250317-loop-uevent-changed-v1-1-cb29cb91b62d@xxxxxxxxxxxxx
> ---
>  drivers/block/loop.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 674527d770dc669e982a2b441af1171559aa427c..09a725710a21171e0adf5888f929ccaf94e98992 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -667,8 +667,8 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
>  
>  	error = 0;
>  done:
> -	/* enable and uncork uevent now that we are done */
>  	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
> +	kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
>  	return error;
>  
>  out_err:
> @@ -1129,8 +1129,8 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
>  	if (partscan)
>  		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
>  
> -	/* enable and uncork uevent now that we are done */
>  	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 0);
> +	kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
>  
>  	loop_global_unlock(lo, is_loop);
>  	if (partscan)
> 
> ---
> base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
> change-id: 20250307-loop-uevent-changed-aa3690f43e03
> 
> Best regards,
> -- 
> Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> 

Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>