Re: [PATCH 11/63] mm: Close races between THP migration and PMDnuma clearing

[Rik van Riel]

On Mon, 30 Sep 2013 09:52:59 +0100
Mel Gorman <mgorman@xxxxxxx> wrote:

> On Fri, Sep 27, 2013 at 02:26:56PM +0100, Mel Gorman wrote:
> > @@ -1732,9 +1732,9 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
> >  	entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> >  	entry = pmd_mkhuge(entry);
> >  
> > -	page_add_new_anon_rmap(new_page, vma, haddr);
> > -
> > +	pmdp_clear_flush(vma, address, pmd);
> >  	set_pmd_at(mm, haddr, pmd, entry);
> > +	page_add_new_anon_rmap(new_page, vma, haddr);
> >  	update_mmu_cache_pmd(vma, address, &entry);
> >  	page_remove_rmap(page);
> >  	/*
> 
> pmdp_clear_flush should have used haddr

Dang, we both discovered this over the weekend? :)

In related news, it looks like update_mmu_cache_pmd should
probably use haddr, too...

----

Subject: mm,numa: make THP migration mmu calls use haddr

The THP NUMA migration function migrate_misplaced_transhuge_page makes
several calls into the architecture specific MMU code. Those calls all
expect the virtual address of the huge page boundary, not the fault
address from somewhere inside the huge page.

This fixes the below bug.

[   80.106362] kernel BUG at mm/pgtable-generic.c:103! 
...
[   80.333720] Call Trace: 
[   80.336450]  [<ffffffff811d5f8b>] migrate_misplaced_transhuge_page+0x1eb/0x500 
[   80.344505]  [<ffffffff811d8883>] do_huge_pmd_numa_page+0x1a3/0x330 
[   80.351497]  [<ffffffff811a3cc5>] handle_mm_fault+0x285/0x370 
[   80.357898]  [<ffffffff816d7df2>] __do_page_fault+0x172/0x5a0 
[   80.364307]  [<ffffffff8137a3dd>] ? trace_hardirqs_off_thunk+0x3a/0x3c 
[   80.371585]  [<ffffffff816d822e>] do_page_fault+0xe/0x10 
[   80.377510]  [<ffffffff816d41c8>] page_fault+0x28/0x30 

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Reported-by: Jan Stancek <jstancek@xxxxxxxxxx>
Tested-by: Jan Stancek <jstancek@xxxxxxxxxx>
---
 mm/migrate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 1e1dbc9..5454151 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1736,10 +1736,10 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 	entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 	entry = pmd_mkhuge(entry);
 
-	pmdp_clear_flush(vma, address, pmd);
+	pmdp_clear_flush(vma, haddr, pmd);
 	set_pmd_at(mm, haddr, pmd, entry);
 	page_add_new_anon_rmap(new_page, vma, haddr);
-	update_mmu_cache_pmd(vma, address, &entry);
+	update_mmu_cache_pmd(vma, haddr, &entry);
 	page_remove_rmap(page);
 	/*
 	 * Finish the charge transaction under the page table lock to

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