> > @@ -232,6 +232,7 @@ void migration_entry_wait(struct mm_stru
> > swp_entry_t entry;
> > struct page *page;
> >
> > +retry:
> > ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> > pte = *ptep;
> > if (!is_swap_pte(pte))
> > @@ -243,11 +244,20 @@ void migration_entry_wait(struct mm_stru
> >
> > page = migration_entry_to_page(entry);
> >
> > - get_page(page);
> > - pte_unmap_unlock(ptep, ptl);
> > - wait_on_page_locked(page);
> > - put_page(page);
> > - return;
> > + /*
> > + * page count might be set to zero by page_freeze_refs()
> > + * in migrate_page_move_mapping().
> > + */
> > + if (get_page_unless_zero(page)) {
> > + pte_unmap_unlock(ptep, ptl);
> > + wait_on_page_locked(page);
> > + put_page(page);
> > + return;
> > + } else {
> > + pte_unmap_unlock(ptep, ptl);
> > + goto retry;
> > + }
> > +
>
> I'm not sure about this part. If it IS needed, I think it would be
> needed independently of the unevictable/putback_lru_page() changes, as
> this race must have already existed.
>
> However, unmap_and_move() replaced the migration entries with bona fide
> pte's referencing the new page before freeing the old page, so I think
> we're OK without this change.
>
Without this part, I can easily get VM_BUG_ON in get_page,
even when processes in cpusets are only bash.
---
kernel BUG at include/linux/mm.h:297!
:
Call Trace:
[<ffffffff80280d82>] ? handle_mm_fault+0x3e5/0x782
[<ffffffff8048c8bf>] ? do_page_fault+0x3d0/0x7a7
[<ffffffff80263ed0>] ? audit_syscall_exit+0x2e4/0x303
[<ffffffff8048a989>] ? error_exit+0x0/0x51
Code: b8 00 00 00 00 00 e2 ff ff 48 8d 1c 02 48 8b 13 f6 c
2 01 75 04 0f 0b eb fe 80 e6 40 48 89 d8 74 04 48 8b 43 10 83 78 08 00 75 04
<0f> 0b eb fe
f0 ff 40 08 fe 45 00 f6 03 01 74 0a 31 f6 48 89 df
RIP [<ffffffff8029c309>] migration_entry_wait+0xcb/0xfa
RSP <ffff81062cc6fe58>
---
I agree that this part should be fixed independently, and
Kamezawa-san has already posted a patch for this.
Thanks,
Daisuke Nishimura.
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