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

[Dongsheng Yang]

在 12/11/2025 3:34 PM, jaeyuel...@lge.com 写道:

From: "jaeyuel.im" <jaeyuel...@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...@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);
                }
        }