PM: hibernate: Freeze kernel threads after image preallocation

Commit 783c81098445 ("PM: hibernate: call preallocate_image() after freeze
prepare") moved hibernate_preallocate_memory() after dpm_prepare() so
that device drivers have the opportunity to release pinned/unswappable
memory during their ->prepare() callback before memory is preallocated
for the snapshot image.

However, that commit also placed hibernate_preallocate_memory() after
freeze_kernel_threads(). While it was assumed during review that swap
I/O submitted via submit_bio() is synchronous and would not depend on
frozen kernel threads, this does not hold in practice. Calling
hibernate_preallocate_memory() with kernel threads frozen leads to
intermittent deadlocks during hibernation.

Inside hibernate_preallocate_memory(), shrink_all_memory() is invoked with
.may_writepage = 1 and .may_swap = 1 to aggressively reclaim and swap out
pages. Any writeback or swap I/O that relies on freezable kernel threads,
block device helpers, or WQ_FREEZABLE workqueues (such as those in storage
drivers, device mapper, or filesystems) deadlocks waiting on tasks that
are stuck in the refrigerator.

Fix this by reordering hibernation_snapshot():
 1. Call dpm_prepare(PMSG_FREEZE) first, allowing device drivers to
    release pinned resources while kernel threads are still active.
 2. Call hibernate_preallocate_memory() second, performing page
    reclaim and swapout while storage layers, workqueues, and kernel
    threads are alive.
 3. Call freeze_kernel_threads() third, only after all memory
    preallocation and swap I/O have completed.

Additionally, restore the call to swsusp_free() in the cleanup path so
that preallocated image memory is properly freed if freeze_kernel_threads()
fails or if TEST_FREEZER is enabled.

Fixes: 783c81098445 ("PM: hibernate: call preallocate_image() after freeze prepare")
Signed-off-by: Florian Schmaus <flo@geekplace.eu>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Tested-by: Matthew Leach <matthew.leach@collabora.com>
Reviewed-by: Matthew Leach <matthew.leach@collabora.com>
Link: https://patch.msgid.link/20260920-fix-hibernation-v1-1-f9940c2d7d7f@geekplace.eu
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

0 files changed, 0 insertions, 0 deletions