On Fri, Dec 12, 2025 at 12:09:55AM +0000, [email protected] wrote:
From: "jaeyuel.im" <[email protected]>
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 <[email protected]>
---
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
