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

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (26/02/06 11:33), Baolin Wang wrote:
> >   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) {
> 
> Your analysis is reasonable. When the system is freezing, khugepaged is
> still trying to swap-in shmem to collapse, which prevents the system from
> entering suspend state. However, it’s not only shmem that will swap in,
> collapsing anonymous folios may also trigger swap-in operations.

Right, I thought about it but wasn't sure.  Could the inner loop (e.g.
collapse_file() in this particular case) loop long enough to fail suspend
w/o ever giving the outer loop (khugepaged_do_scan()) a chance to freeze?