[PATCH 6.6 088/175] PM: hibernate: Drain trailing zero pages on userspace restore

Greg Kroah-Hartman
2026-03-31T16:27:24Z

From: Alberto Garcia <berto@igalia.com>

[ Upstream commit 734eba62cd32cb9ceffa09e57cdc03d761528525 ]

Commit 005e8dddd497 ("PM: hibernate: don't store zero pages in the
image file") added an optimization to skip zero-filled pages in the
hibernation image. On restore, zero pages are handled internally by
snapshot_write_next() in a loop that processes them without returning
to the caller.

With the userspace restore interface, writing the last non-zero page
to /dev/snapshot is followed by the SNAPSHOT_ATOMIC_RESTORE ioctl. At
this point there are no more calls to snapshot_write_next() so any
trailing zero pages are not processed, snapshot_image_loaded() fails
because handle->cur is smaller than expected, the ioctl returns -EPERM
and the image is not restored.

The in-kernel restore path is not affected by this because the loop in
load_image() in swap.c calls snapshot_write_next() until it returns 0.
It is this final call that drains any trailing zero pages.

Fixed by calling snapshot_write_next() in snapshot_write_finalize(),
giving the kernel the chance to drain any trailing zero pages.

Fixes: 005e8dddd497 ("PM: hibernate: don't store zero pages in the image file")
Signed-off-by: Alberto Garcia <berto@igalia.com>
Acked-by: Brian Geffon <bgeffon@google.com>
Link: https://patch.msgid.link/ef5a7c5e3e3dbd17dcb20efaa0c53a47a23498bb.1773075892.git.berto@igalia.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/power/snapshot.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index ea52417375a4e..c3ad93fc24e64 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -2866,6 +2866,17 @@ int snapshot_write_finalize(struct snapshot_handle *handle)
{
int error;

+ /*
+ * Call snapshot_write_next() to drain any trailing zero pages,
+ * but make sure we're in the data page region first.
+ * This function can return PAGE_SIZE if the kernel was expecting
+ * another copy page. Return -ENODATA in that situation.
+ */
+ if (handle->cur > nr_meta_pages + 1) {
+ error = snapshot_write_next(handle);
+ if (error)
+ return error > 0 ? -ENODATA : error;
+ }
copy_last_highmem_page();
error = hibernate_restore_protect_page(handle->buffer);
/* Do that only if we have loaded the image entirely */
--
2.53.0