Re: [PATCH 1/2] hugetlbfs: stop setting VM_DONTDUMP in initializingvma(VM_HUGETLB)

[Konstantin Khlebnikov]

Naoya Horiguchi wrote:
> On Thu, Mar 28, 2013 at 09:03:16PM +0400, Konstantin Khlebnikov wrote:
>> Naoya Horiguchi wrote:
>>> Currently we fail to include any data on hugepages into coredump,
>>> because VM_DONTDUMP is set on hugetlbfs's vma. This behavior was recently
>>> introduced by commit 314e51b98 "mm: kill vma flag VM_RESERVED and
>>> mm->reserved_vm counter". This looks to me a serious regression,
>>> so let's fix it.
>>
>> That was introduced in my patch? Really?
>> Here was VM_RESERVED and it had the same effect as VM_DONTDUMP. At least I thought so.
> 
> vma_dump_size() does like this (the diff is the one in 314e51b98):
> 
>     static unsigned long vma_dump_size(struct vm_area_struct *vma,
>     				   unsigned long mm_flags)
>     {
>     #define FILTER(type)	(mm_flags&  (1UL<<  MMF_DUMP_##type))
> 
>     	/* always dump the vdso and vsyscall sections */
>     	if (always_dump_vma(vma))
>     		goto whole;
> 
>    	if (vma->vm_flags&  VM_DONTDUMP)
>     		return 0;
> 
>     	/* Hugetlb memory check */
>     	if (vma->vm_flags&  VM_HUGETLB) {
>     		if ((vma->vm_flags&  VM_SHARED)&&  FILTER(HUGETLB_SHARED))
>     			goto whole;
>     		if (!(vma->vm_flags&  VM_SHARED)&&  FILTER(HUGETLB_PRIVATE))
>     			goto whole;
>     	}
> 
>     	/* Do not dump I/O mapped devices or special mappings */
>    -	if (vma->vm_flags&  (VM_IO | VM_RESERVED))
>    +	if (vma->vm_flags&  VM_IO)
>     		return 0;
> 
> We have hugetlb memory check after VM_DONTDUMP check, so the following
> changed the behavior.

Ok, I missed this in my patch.

> 
>    --- a/fs/hugetlbfs/inode.c
>    +++ b/fs/hugetlbfs/inode.c
>    @@ -110,7 +110,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
>             * way when do_mmap_pgoff unwinds (may be important on powerpc
>             * and ia64).
>             */
>    -       vma->vm_flags |= VM_HUGETLB | VM_RESERVED;
>    +       vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND | VM_DONTDUMP;
>            vma->vm_ops =&hugetlb_vm_ops;
> 
>            if (vma->vm_pgoff&  (~huge_page_mask(h)>>  PAGE_SHIFT))
> 
> I think we don't have to set VM_DONTDUMP on hugetlbfs's vma.

Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>

> 
> Thanks,
> Naoya

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