Re: [Bugme-new] [Bug 13302] New: "bad pmd" on fork() of process with hugepage shared memory segments attached

[Mel Gorman <mel@csn.ul.ie>]

On Sun, May 24, 2009 at 10:44:29PM +0900, KOSAKI Motohiro wrote:
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > --- 
> >  arch/x86/mm/hugetlbpage.c |    6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> > index 8f307d9..16e4bcc 100644
> > --- a/arch/x86/mm/hugetlbpage.c
> > +++ b/arch/x86/mm/hugetlbpage.c
> > @@ -26,12 +26,16 @@ static unsigned long page_table_shareable(struct vm_area_struct *svma,
> >  	unsigned long sbase = saddr & PUD_MASK;
> >  	unsigned long s_end = sbase + PUD_SIZE;
> >  
> > +	/* Allow segments to share if only one is locked */
> > +	unsigned long vm_flags = vma->vm_flags & ~VM_LOCKED;
> > +	unsigned long svm_flags = vma->vm_flags & ~VM_LOCKED;
>                                   svma?
> 

/me slaps self

svma indeed.

With the patch corrected, I still cannot trigger the bad pmd messages as
applied so I'm convinced the bug is related to hugetlb pagetable
sharing and this is more or less the fix. Any opinions?

>  - kosaki
> 
> > +
> >  	/*
> >  	 * match the virtual addresses, permission and the alignment of the
> >  	 * page table page.
> >  	 */
> >  	if (pmd_index(addr) != pmd_index(saddr) ||
> > -	    vma->vm_flags != svma->vm_flags ||
> > +	    vm_flags != svm_flags ||
> >  	    sbase < svma->vm_start || svma->vm_end < s_end)
> >  		return 0;
> >  
> 
> 
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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