From 734eba62cd32cb9ceffa09e57cdc03d761528525 Mon Sep 17 00:00:00 2001 From: Alberto Garcia Date: Mon, 9 Mar 2026 18:39:41 +0100 Subject: [PATCH] PM: hibernate: Drain trailing zero pages on userspace restore 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 Acked-by: Brian Geffon Link: https://patch.msgid.link/ef5a7c5e3e3dbd17dcb20efaa0c53a47a23498bb.1773075892.git.berto@igalia.com Signed-off-by: Rafael J. Wysocki --- kernel/power/snapshot.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c index 6e1321837c66..a564650734dc 100644 --- a/kernel/power/snapshot.c +++ b/kernel/power/snapshot.c @@ -2855,6 +2855,17 @@ 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 */