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

Dongsheng Yang
2025-12-11T08:20:07Z

在 12/11/2025 3:34 PM, jaeyuel.im@lge.com 写道:
> From: "jaeyuel.im" <jaeyuel.im@lge.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@lge.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);
> }
> }
>