PM: hibernate: align default resume swap with image-device checks

snapshot_open(O_RDONLY) pins the configured default resume swap area for hibernation image writes, but it does not fully propagate that choice to the image-device checks used by the block layer.

In particular, snapshot_open() uses swsusp_resume_device without swsusp_resume_block when pinning the default resume swap area, and it leaves snapshot_state.dev unset even after the pin succeeds. As a result, the default resume swap selected at open time is not kept aligned with is_hibernate_resume_dev() and can still be rejected by the block layer in blkdev_write_iter() with -ETXTBSY until user space explicitly selects the same area via SNAPSHOT_SET_SWAP_AREA.

Use swsusp_resume_block when pinning the default resume swap area and record the device immediately after a successful pin so that the hibernation image-device bookkeeping matches the configured resume area. Also clear snapshot_state.dev on the open-time error path so it never advertises a session that failed to fully open.

uswsusp itself is not affected because it always calls SNAPSHOT_SET_SWAP_AREA right after open, which immediately overrides snapshot_state.dev and re-pins the swap area. The user-visible change is for minimal hibernation user space that relies on resume= and resume_offset= alone: such tools no longer have to restate the resume area via SNAPSHOT_SET_SWAP_AREA just to satisfy blkdev_write_iter()'s IS_SWAPFILE gate or to obtain SWP_HIBERNATION swapoff protection. This also matches the intent of the existing "The image device should be accessible" comment in snapshot_open(). For the configured default resume area, this gives snapshot_open() the same pin and recorded-device state that SNAPSHOT_SET_SWAP_AREA would establish for that same area, so user space relying on resume= and resume_offset= does not need a follow-up SNAPSHOT_SET_SWAP_AREA just to satisfy the IS_SWAPFILE gate and obtain swapoff protection.

---
Based on linux-next/master at commit e6efabc0afca ("Add linux-next specific files for 20260414").

Tested in QEMU: with swap on a block device pointed to by /sys/power/resume, opening /dev/snapshot O_RDONLY and then writing to the swap block device returned -ETXTBSY before this change and -ENOSPC (i.e. no longer rejected by the IS_SWAPFILE gate) after.

 kernel/power/user.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index d0fcfba7ac23..c51b8185de4b 100644
@@ -69,9 +69,13 @@ static int snapshot_open(struct inode *inode, struct file *filp)
 	data = &snapshot_state;
 	filp->private_data = data;
 	memset(&data->handle, 0, sizeof(struct snapshot_handle));
+	data->dev = 0;
 	if ((filp->f_flags & O_ACCMODE) == O_RDONLY) {
 		/* Hibernating.  The image device should be accessible. */
-		data->swap = pin_hibernation_swap_type(swsusp_resume_device, 0);
+		data->swap = pin_hibernation_swap_type(swsusp_resume_device,
+						      swsusp_resume_block);
+		if (data->swap >= 0)
+			data->dev = swsusp_resume_device;
 		data->mode = O_RDONLY;
 		data->free_bitmaps = false;
 		error = pm_notifier_call_chain_robust(PM_HIBERNATION_PREPARE, PM_POST_HIBERNATION);

@@ -92,13 +96,13 @@ static int snapshot_open(struct inode *inode, struct file *filp)
 	}
 	if (error) {
 		unpin_hibernation_swap_type(data->swap);
+		data->dev = 0;
 		hibernate_release();
 	}
 
 	data->frozen = false;
 	data->ready = false;
 	data->platform_support = false;
-	data->dev = 0;
 
  Unlock:
 	unlock_system_sleep(sleep_flags);

2.43.0

On Wed, Apr 15, 2026 at 05:12:13PM +0900, DaeMyung Kang wrote:

Hello DaeMyung again :)

So, to summarize: if the resume area and offset are fully specified via
kernel parameters, it should work with hibernation image write properly with just snapshot_open() without needing an explicit ioctl call, right? And since uswsusp
hibernation tools currently use the ioctl, this hasn't been a visible
issue so far.