linux-kernel - Re: [PATCH] dm init: ensure block device is ready before creating mapped device

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Message-ID: <ef533f19-96a9-4e14-be1d-2290677cbfd2@linux.dev>
Date: Thu, 11 Dec 2025 16:19:56 +0800
From: Dongsheng Yang <dongsheng.yang@...ux.dev>
To: jaeyuel.im@....com, Alasdair Kergon <agk@...hat.com>,
 Mike Snitzer <snitzer@...nel.org>, Mikulas Patocka <mpatocka@...hat.com>
Cc: dm-devel@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dm init: ensure block device is ready before creating
 mapped device


在 12/11/2025 3:34 PM, jaeyuel.im@....com 写道:
> From: "jaeyuel.im" <jaeyuel.im@....com>
>
> The current implementation of dm_init_init() uses early_lookup_bdev() to
> wait for the device node to appear. However, early_lookup_bdev() only
> verifies that the device node exists and returns the dev_t. It does not
> guarantee that the underlying block device structure is fully initialized
> and ready for I/O operations or to be opened.
>
> On certain platforms (e.g., embedded systems with specific storage
> drivers), this can lead to a race condition where dm_early_create()
> attempts to open the device immediately after early_lookup_bdev() returns,
> but fails because the device is not yet fully ready. This results in boot
> failures as the mapped device cannot be created.
>
> This patch adds an additional check using blkdev_get_no_open() after
> early_lookup_bdev() returns. This ensures that the struct block_device is
> actually available and the device is ready to be opened, effectively
> preventing the race condition.
>
> Signed-off-by: jaeyuel.im <jaeyuel.im@....com>
> ---
>   drivers/md/dm-init.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
>
> diff --git a/drivers/md/dm-init.c b/drivers/md/dm-init.c
> index ff9420f06483..76b84ca39906 100644
> --- a/drivers/md/dm-init.c
> +++ b/drivers/md/dm-init.c
> @@ -299,10 +299,24 @@ static int __init dm_init_init(void)
>   	for (i = 0; i < ARRAY_SIZE(waitfor); i++) {
>   		if (waitfor[i]) {
>   			dev_t dev;
> +			struct block_device *bdev;
>   
>   			DMINFO("waiting for device %s ...", waitfor[i]);
>   			while (early_lookup_bdev(waitfor[i], &dev))
>   				fsleep(5000);
> +
> +			/*
> +			 * early_lookup_bdev() only checks if the device node exists and
> +			 * returns the dev_t. It does not guarantee that the underlying
> +			 * block device is fully initialized and ready to be opened. On
> +			 * some platforms, this can lead to a race condition where
> +			 * dm_early_create() fails because the device is not yet ready.
> +			 * Ensure the block device is truly available by attempting to
> +			 * get it.
> +			 */
> +			while (!(bdev = blkdev_get_no_open(dev)))

You need to pass autoload parameter for new blkdev_get_no_open()

"struct block_device *blkdev_get_no_open(dev_t dev, bool autoload)"


Thanx

> +				fsleep(5000);
> +			blkdev_put_no_open(bdev);
>   		}
>   	}
>