Re: [PATCH] dm init: ensure device probing has finished in dm-mod.waitfor=

[Francesco Valla <francesco@valla.it>]

Hello Guillaume,

On Tue, Mar 17, 2026 at 10:32:28PM +0100, Guillaume Gonnet wrote:
> The early_lookup_bdev() function returns successfully when the disk
> device is present but not necessarily its partitions. In this situation,
> dm_early_create() fails as the partition block device does not exist
> yet.
> 
> In my case, this phenomenon occurs quite often because the device is
> an SD card with slow reading times, on which kernel takes time to
> enumerate available partitions.
> 

I am now in the same situation, but I have seen the behavior also on
"fast" eMMC devices probing on slow single-core processors.

> Fortunately, the underlying device is back to "probing" state while
> enumerating partitions. Waiting for all probing to end is enough to fix
> this issue.
> 
> That's also the reason why this problem never occurs with rootwait=
> parameter: the while loop inside wait_for_root() explicitly waits for
> probing to be done and then the function calls async_synchronize_full().
> These lines were omitted in 035641b, even though the commit says it's
> based on the rootwait logic...
> 
> Anyway, calling wait_for_device_probe() after our while loop does the
> job (it both waits for probing and calls async_synchronize_full).
> 
> Fixes: 035641b01e72 ("dm init: add dm-mod.waitfor to wait for asynchronously probed block devices")
> Signed-off-by: Guillaume Gonnet <ggonnet.linux@gmail.com>
> ---
> 
> Hello,
> 
> This patch is my attempt to fix the dm-mod.waitfor= issue. I had this
> fix for quite a while now, but I've never made the effort to contribute
> until recently.
> 
> Some have tried to fix it this issue in the past but without finding
> its real root cause (ie. not waiting for device probe to end).
> 
> Here are the links to those patches, for reference:
> https://lore.kernel.org/all/b5c5cd56-b9dd-4368-a8e1-b9e0a07b79b4@schwermer.no/
> https://lore.kernel.org/all/20250410080056.43247-1-chanho.min@lge.com/
> https://lore.kernel.org/dm-devel/20251211073426.123026-1-jaeyuel.im@lge.com/
> 
>  drivers/md/dm-init.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-init.c b/drivers/md/dm-init.c
> index 7403823384c5..c1bacba92c65 100644
> --- a/drivers/md/dm-init.c
> +++ b/drivers/md/dm-init.c
> @@ -303,8 +303,10 @@ static int __init dm_init_init(void)
>  		}
>  	}
>  
> -	if (waitfor[0])
> +	if (waitfor[0]) {
> +		wait_for_device_probe();
>  		DMINFO("all devices available");
> +	}
>  
>  	list_for_each_entry(dev, &devices, list) {
>  		if (dm_early_create(&dev->dmi, dev->table,
> -- 
> 2.43.0
>

Reviewed-by: Francesco Valla <francesco@valla.it>
Tested-by: Francesco Valla <francesco@valla.it>


Thank you!

Regards,
Francesco