On Tue, Aug 30, 2016 at 06:59:38PM +0800, wei.guo.simon@xxxxxxxxx wrote:
> From: Simon Guo <wei.guo.simon@xxxxxxxxx>
>
> In do_mlock(), the check against locked memory limitation
> has a hole which will fail following cases at step 3):
> 1) User has a memory chunk from addressA with 50k, and user
> mem lock rlimit is 64k.
> 2) mlock(addressA, 30k)
> 3) mlock(addressA, 40k)
>
> The 3rd step should have been allowed since the 40k request
> is intersected with the previous 30k at step 2), and the
> 3rd step is actually for mlock on the extra 10k memory.
>
> This patch checks vma to caculate the actual "new" mlock
> size, if necessary, and ajust the logic to fix this issue.
>
> Signed-off-by: Simon Guo <wei.guo.simon@xxxxxxxxx>
Looks reasonable to me. Few nitpicks below.
> ---
> mm/mlock.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 49 insertions(+)
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 14645be..9283187 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -617,6 +617,43 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
> return error;
> }
>
> +/*
> + * Go through vma areas and sum size of mlocked
> + * vma pages, as return value.
> + * Note deferred memory locking case(mlock2(,,MLOCK_ONFAULT)
> + * is also counted.
> + * Return value: previously mlocked page counts
> + */
> +static int count_mm_mlocked_page_nr(struct mm_struct *mm,
> + unsigned long start, size_t len)
> +{
> + struct vm_area_struct *vma;
> + int count = 0;
> +
> + if (mm == NULL)
> + mm = current->mm;
> +
> + vma = find_vma(mm, start);
> + if (vma == NULL)
> + vma = mm->mmap;
> +
> + for (; vma ; vma = vma->vm_next) {
> + if (start + len <= vma->vm_start)
> + break;
for (; vma && start + len <= vma->vm_start; vma = vma->vm_next) {
> + if (vma->vm_flags && VM_LOCKED) {
> + if (start > vma->vm_start)
> + count -= (start - vma->vm_start);
> + if (start + len < vma->vm_end) {
> + count += start + len - vma->vm_start;
> + break;
> + }
> + count += vma->vm_end - vma->vm_start;
> + }
> + }
> +
> + return (PAGE_ALIGN(count) >> PAGE_SHIFT);
Redundant parenthesis.
And do we need PAGE_ALIGN() here? Caller already aligned 'len', and vma
boundaries are alinged.
> +}
> +
> static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t flags)
> {
> unsigned long locked;
> @@ -639,6 +676,18 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
> return -EINTR;
>
> locked += current->mm->locked_vm;
> + if ((locked > lock_limit) && (!capable(CAP_IPC_LOCK))) {
> + /*
> + * It is possible that the regions requested
> + * intersect with previously mlocked areas,
> + * that part area in "mm->locked_vm" should
> + * not be counted to new mlock increment
> + * count. So check and adjust locked count
> + * if necessary.
> + */
> + locked -= count_mm_mlocked_page_nr(current->mm,
> + start, len);
> + }
>
> /* check against resource limits */
> if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
> --
> 1.8.3.1
>
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--
Kirill A. Shutemov
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