[stable-6.6.y] mm: khugepaged refuses to freeze

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Greetings,

I'm looking at a slightly unusual issue where khugepaged refuses to
freeze during system suspend:

...
 PM: suspend entry (s2idle)
 Filesystems sync: 0.003 seconds
 Freezing user space processes
 Freezing user space processes completed (elapsed 0.003 seconds)
 OOM killer disabled.
 Freezing remaining freezable tasks
 Freezing remaining freezable tasks failed after 20.004 seconds (1 tasks refusing to freeze, wq_busy=0):
 task:khugepaged      state:D stack:0     pid:1345  ppid:2      flags:0x00004000
 Call Trace:
  <TASK>
  schedule+0x523/0x16a0
  ? sysvec_apic_timer_interrupt+0xf/0x90
  ? asm_sysvec_apic_timer_interrupt+0x16/0x20
  ? wait_for_completion_io_timeout+0xc5/0x170
  schedule_timeout+0x23b/0x6e0
  ? __pfx_process_timeout+0x10/0x10
  ? wait_for_completion_io_timeout+0xc5/0x170
  io_schedule_timeout+0x3f/0x80
  wait_for_completion_io_timeout+0xe4/0x170
  submit_bio_wait+0x79/0xc0
  swap_readpage+0x150/0x2d0
  ? __pfx_submit_bio_wait_endio+0x10/0x10
  swap_cluster_readahead+0x3be/0x750
  ? __pfx_workingset_update_node+0x10/0x10
  shmem_swapin+0xa7/0x100
  shmem_swapin_folio+0xcd/0x2e0
  shmem_get_folio+0x237/0x580
  collapse_file+0x247/0x1280
  hpage_collapse_scan_file+0x26e/0x380
  khugepaged+0x43b/0x810
  kthread+0xfb/0x120
  ? __pfx_khugepaged+0x10/0x10
  ? __pfx_kthread+0x10/0x10
  ret_from_fork+0x38/0x50
  ? __pfx_kthread+0x10/0x10
  ret_from_fork_asm+0x1b/0x30
  </TASK>
...

The system is using zram swap.  I wonder if khugepaged should
be suspend/freeze aware.  Does something like below make sense?
Or is the problem elsewhere?

---
 mm/khugepaged.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index eff9e3061925..fa6a018b20a8 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1894,6 +1894,9 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 		xas_set(&xas, index);
 		folio = xas_load(&xas);
 
+		if (try_to_freeze())
+			goto xa_unlocked;
+
 		VM_BUG_ON(index != xas.xa_index);
 		if (is_shmem) {
 			if (!folio) {
-- 
2.53.0.rc2.204.g2597b5adb4-goog