Re: [PATCH v2] dm init: ensure block device is ready before creating mapped device

Sasha Levin
2026-01-03T22:50:30Z

On Fri, Dec 12, 2025 at 12:09:55AM +0000, jaeyuel.im@lge.com wrote:
>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.
>
>Changes in v2:
>- Pass autoload parameter for new blkdev_get_no_open()
>
>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 b37bbe762500..b3905e094ffc 100644
>--- a/drivers/md/dm-init.c
>+++ b/drivers/md/dm-init.c
>@@ -296,10 +296,24 @@ 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, false)))

This breaks the build when CONFIG_DM_INIT=y:

drivers/md/dm-init.c:314:41: error: implicit declaration of function 'blkdev_get_no_open'; did you mean 'blkdev_get_zone_info'? [-Wimplicit-function-declaration]
314 | while (!(bdev = blkdev_get_no_open(dev, false)))
drivers/md/dm-init.c:316:25: error: implicit declaration of function 'blkdev_put_no_open' [-Wimplicit-function-declaration]
316 | blkdev_put_no_open(bdev);

The problem is that blkdev_get_no_open() and blkdev_put_no_open() are declared
in block/blk.h, which is internal to the block layer and not accessible from
drivers/md/. These functions need to be exported to a public header, or
dm-init.c needs to use a different API.

--
Thanks,
Sasha