On Fri, Nov 08, 2019 at 09:01:44PM +0800, Li Xinhai wrote:
> mbind() is required to report EFAULT if range, specified by addr and len,
> contains unmapped holes. In current implementation, below rules are applied
> for this checking:
> 1 Unmapped holes at any part of the specified range should be reported as
> EFAULT if mbind() for none MPOL_DEFAULT cases;
> 2 Unmapped holes at any part of the specified range should be ignored (do
> not reprot EFAULT) if mbind() for MPOL_DEFAULT case;
> 3 The whole range in an unmapped hole should be reported as EFAULT;
> Note that rule 2 does not fullfill the mbind() API definition, but since
> that behavior has existed for long days (the internal flag
> MPOL_MF_DISCONTIG_OK is for this purpose), this patch does not plan to
> change it.
>
> In current code, application observed inconsistent behavior on rule 1 and
> rule 2 respectively. That inconsistency is fixed as below details.
>
> Cases of rule 1:
> 1) Hole at head side of range. Current code reprot EFAULT, no change by
> this patch.
> [ vma ][ hole ][ vma ]
> [ range ]
> 2) Hole at middle of range. Current code report EFAULT, no change by
> this patch.
> [ vma ][ hole ][ vma ]
> [ range ]
> 3) Hole at tail side of range. Current code do not report EFAULT, this
> patch fix it.
> [ vma ][ hole ][ vma ]
> [ range ]
>
> Cases of rule 2:
> 1) Hole at head side of range. Current code reprot EFAULT, this patch
> fix it.
> [ vma ][ hole ][ vma ]
> [ range ]
> 2) Hole at middle of range. Current code do not report EFAULT, no change
> by this patch.
> this patch.
> [ vma ][ hole ][ vma]
> [ range ]
> 3) Hole at tail side of range. Current code do not report EFAULT, no
> change by this patch.
> [ vma ][ hole ][ vma]
> [ range ]
>
> This patch has no changes to rule 3.
>
> The unmapped hole checking can also be handled by using .pte_hole(),
> instead of .test_walk(). But .pte_hole() is called for holes inside and
> outside vma, which causes more cost, so this patch keeps the original
> design with .test_walk().
>
> Fixes: 6f4576e3687b ("mempolicy: apply page table walker on queue_pages_range()")
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: linux-man <linux-man@xxxxxxxxxxxxxxx>
> Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
> ---
> mm/mempolicy.c | 40 +++++++++++++++++++++++++++-------------
> 1 file changed, 27 insertions(+), 13 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 807f06f..c697b29 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -410,7 +410,9 @@ struct queue_pages {
> struct list_head *pagelist;
> unsigned long flags;
> nodemask_t *nmask;
> - struct vm_area_struct *prev;
> + unsigned long start;
> + unsigned long end;
> + struct vm_area_struct *first;
> };
>
> /*
> @@ -619,14 +621,20 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
> unsigned long flags = qp->flags;
>
> /* range check first */
> - if (!(flags & MPOL_MF_DISCONTIG_OK)) {
> - if (!vma->vm_next && vma->vm_end < end)
> - return -EFAULT;
> - if (qp->prev && qp->prev->vm_end < vma->vm_start)
> + VM_BUG_ON((vma->vm_start > start) || (vma->vm_end < end));
> +
> + if (!qp->first) {
> + qp->first = vma;
> + if (!(flags & MPOL_MF_DISCONTIG_OK) &&
> + (qp->start < vma->vm_start))
> + /* hole at head side of range */
> return -EFAULT;
> }
> -
> - qp->prev = vma;
> + if (!(flags & MPOL_MF_DISCONTIG_OK) &&
> + ((vma->vm_end < qp->end) &&
You here have a trailing whitespace.
Otherwise, looks good to me.
Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
