On Thu, Mar 10, 2016 at 11:52:54AM -0800, Andrew Morton wrote:
> On Thu, 10 Mar 2016 17:54:06 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> > split_huge_pmd() tries to munlock page with munlock_vma_page(). That
> > requires the page to locked.
> >
> > If the is locked by caller, we would get a deadlock:
> >
> > ...
> >
> > I don't think the deadlock is triggerable without split_huge_page()
> > simplifilcation patchset.
> >
> > But munlock_vma_page() here is wrong: we want to munlock the page
> > unconditionally, no need in rmap lookup, that munlock_vma_page() does.
> >
> > Let's use clear_page_mlock() instead. It can be called under ptl.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Fixes: ee0b79212791 ("thp: allow mlocked THP again")
>
> This is the incorrect hash (or something weird happened at my end).
> I'm seeing
>
> commit e90309c9f7722db4ff5bce3b9e6e04d1460f2553
> Author: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Fri Jan 15 16:54:33 2016 -0800
>
> thp: allow mlocked THP again
>
> That's the second time this has happened this week so please
> double-check whatever you're doing here?
>
>
> The patch itself doesn't apply to mainline, which is a bit strange
> given that it "Fixes" a bug in an already-mainlined patch. The patch
> as-sent depends upon
> thp-rewrite-freeze_page-unfreeze_page-with-generic-rmap-walkers.patch,
> so I have queued it after that patch.
Here's a patch that can be applied mainline. Just in case.
>From b3f05a96497745745730d4ce0e8569acb286758b Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Date: Tue, 8 Mar 2016 18:58:07 +0300
Subject: [PATCH] thp: fix deadlock in split_huge_pmd()
split_huge_pmd() tries to munlock page with munlock_vma_page(). That
requires the page to locked.
If the is locked by caller, we would get a deadlock:
Unable to find swap-space signature
INFO: task trinity-c85:1907 blocked for more than 120 seconds.
Not tainted 4.4.0-00032-gf19d0bdced41-dirty #1606
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
trinity-c85 D ffff88084d997608 0 1907 309 0x00000000
ffff88084d997608 ffff880800000002 ffff880800000001 ffffffff8348eb60
ffffffff82a41be0 1ffff10109b32eb0 ffff88084e18de98 ffff88085635e858
ffff88085635e840 ffff8802b63f16c0 ffff88084e18db00 0000000041b58ab3
Call Trace:
[<ffffffff828ac670>] ? __sched_text_start+0x8/0x8
[<ffffffff811e9f70>] ? debug_show_all_locks+0x280/0x280
[<ffffffff81234a67>] ? debug_lockdep_rcu_enabled+0x77/0x90
[<ffffffff828af07f>] schedule+0x9f/0x1c0
[<ffffffff828b921e>] schedule_timeout+0x48e/0x600
[<ffffffff828b8d90>] ? console_conditional_schedule+0x40/0x40
[<ffffffff8126b423>] ? ktime_get+0x143/0x190
[<ffffffff811e5f55>] ? trace_hardirqs_on_caller+0x405/0x590
[<ffffffff811e60ed>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff8126b3db>] ? ktime_get+0xfb/0x190
[<ffffffff812f0ce6>] ? __delayacct_blkio_start+0x46/0x90
[<ffffffff828afc73>] io_schedule_timeout+0x1c3/0x390
[<ffffffff828b0689>] bit_wait_io+0x29/0xd0
[<ffffffff828b0004>] __wait_on_bit_lock+0x94/0x140
[<ffffffff828b0660>] ? bit_wait+0xc0/0xc0
[<ffffffff813aaa24>] __lock_page+0x1d4/0x280
[<ffffffff813aa850>] ? page_endio+0x2f0/0x2f0
[<ffffffff811d0390>] ? wake_atomic_t_function+0x220/0x220
[<ffffffff81181095>] ? __might_sleep+0x95/0x1a0
[<ffffffff814f0238>] __split_huge_pmd+0x5a8/0x10f0
[<ffffffff814f3849>] split_huge_pmd_address+0x1d9/0x230
[<ffffffff81473ef0>] try_to_unmap_one+0x540/0xc70
[<ffffffff814739b0>] ? page_remove_rmap+0x8d0/0x8d0
[<ffffffff8146f3b4>] rmap_walk_anon+0x284/0x810
[<ffffffff8146d9f0>] ? invalid_mkclean_vma+0x50/0x50
[<ffffffff8147815e>] rmap_walk_locked+0x11e/0x190
[<ffffffff81478381>] try_to_unmap+0x1b1/0x4b0
[<ffffffff814781d0>] ? rmap_walk_locked+0x190/0x190
[<ffffffff814739b0>] ? page_remove_rmap+0x8d0/0x8d0
[<ffffffff8146eac0>] ? rmap_walk_file+0x7b0/0x7b0
[<ffffffff81476440>] ? page_get_anon_vma+0x810/0x810
[<ffffffff8146d9f0>] ? invalid_mkclean_vma+0x50/0x50
[<ffffffff814f3bea>] ? total_mapcount+0xea/0x3e0
[<ffffffff814f437d>] split_huge_page_to_list+0x49d/0x18a0
[<ffffffff8143e386>] follow_page_mask+0xa36/0xea0
[<ffffffff814e0033>] SyS_move_pages+0xaf3/0x1570
[<ffffffff814df64c>] ? SyS_move_pages+0x10c/0x1570
[<ffffffff814df540>] ? migrate_pages+0x4be0/0x4be0
[<ffffffff812346a3>] ? rcu_read_lock_sched_held+0xa3/0x130
[<ffffffff814cb80f>] ? kmem_cache_free+0x31f/0x370
[<ffffffff8154382d>] ? putname+0x5d/0x140
[<ffffffff81002004>] ? lockdep_sys_exit_thunk+0x12/0x14
[<ffffffff828bbc17>] entry_SYSCALL_64_fastpath+0x12/0x6b
2 locks held by trinity-c85/1907:
#0: (&mm->mmap_sem){++++++}, at: [<ffffffff814dfe73>] SyS_move_pages+0x933/0x1570
#1: (&anon_vma->rwsem){++++..}, at: [<ffffffff814f42e2>] split_huge_page_to_list+0x402/0x18a0
I don't think the deadlock is triggerable without split_huge_page()
simplifilcation patchset.
But munlock_vma_page() here is wrong: we want to munlock the page
unconditionally, no need in rmap lookup, that munlock_vma_page() does.
Let's use clear_page_mlock() instead. It can be called under ptl.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Fixes: e90309c9f772 ("thp: allow mlocked THP again")
---
mm/huge_memory.c | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e10a4fee88d2..31ccc0131f3a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2951,29 +2951,20 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
{
spinlock_t *ptl;
struct mm_struct *mm = vma->vm_mm;
- struct page *page = NULL;
unsigned long haddr = address & HPAGE_PMD_MASK;
mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
ptl = pmd_lock(mm, pmd);
if (pmd_trans_huge(*pmd)) {
- page = pmd_page(*pmd);
+ struct page *page = pmd_page(*pmd);
if (PageMlocked(page))
- get_page(page);
- else
- page = NULL;
+ clear_page_mlock(page);
} else if (!pmd_devmap(*pmd))
goto out;
__split_huge_pmd_locked(vma, pmd, haddr, false);
out:
spin_unlock(ptl);
mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
- if (page) {
- lock_page(page);
- munlock_vma_page(page);
- unlock_page(page);
- put_page(page);
- }
}
static void split_huge_pmd_address(struct vm_area_struct *vma,
--
Kirill A. Shutemov
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