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

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Konstantin Khlebnikov wrote:
> 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@openvz.org>

hugetlb coredump filter also should be fixed in this way:

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1154,6 +1154,7 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma,
                        goto whole;
                if (!(vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_PRIVATE))
                        goto whole;
+               return 0;
        }

        /* Do not dump I/O mapped devices or special mappings */

> 
>>
>> Thanks,
>> Naoya
>