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

[Chanho Min <chanho.min@lge.com>]

On Thu, Mar 19, 2026 at 10:05:46AM +0100, Guillaume Gonnet wrote:
> Hello Chanho,
> 
> > This patch seems overly optimistic.
> > wait_for_device_probe() only waits for driver probe() callbacks to finish.
> > However, partition devices (e.g. /dev/mmcblk0p3) are often created
> > asynchronously after the parent disk probe has completed.
> 
> This patch does work and fix the issue. I let you read my detailed
> explanation on how it does in my latest message on the mailing list:
> https://lore.kernel.org/dm-devel/DH6MMYX3TX5Y.R3N3IX6370ED@gmail.com/
> 
> Basically, it replicates what was made for rootwait= argument, which has
> the same objectives but doesn't suffer from this issue.
Hi, Guillaume

I have verified that your patch does fix the issue I was seeing.
Given that blkdev_get_no_open() is no longer a public interface,
your approach seems to be the most suitable solution currently available.
Calling wait_for_device_probe() twice doesn't look particularly elegant,
but I can understand the reasoning behind it.

Reviewed-by: Chanho Min <chanho.min@lge.com>

Thanks
Chanho
> 
> > The previous per-device polling loop was much more robust for dm-verity rootfs
> > use cases without an initramfs. Replacing it with a single call to
> > wait_for_device_probe() is likely a regression.
> > Instead, we should restore (and possibly improve) proper per-device waiting
> > using blkdev_get_no_open() in a loop until the actual partition appears.
> >
> > That said, Christoph also pointed out in the thread that dm-init is inherently
> > fragile, and the proper long-term solution is to use initramfs + udev.
> 
> The blkdev_get_no_open() is an internal function of the block system.
> Christoph moved it out of public headers last year (see commit c632021).
> As you said, he is not a great fan of this dm-init wait mechanism so I'm
> pretty sure he won't let you make these functions public again. My patch
> does not depend of the block system at all, while still fixing the issue.
> 
> Guillaume