[PATCH v6 updated 9/11] mm/mremap: Fix race between mremap and pageout
torvalds at linux-foundation.org
Tue May 25 03:16:43 AEST 2021
On Mon, May 24, 2021 at 3:38 AM Aneesh Kumar K.V
<aneesh.kumar at linux.ibm.com> wrote:
> Avoid the above race with MOVE_PMD by holding pte ptl in mremap and waiting for
> parallel pagetable walk to finish operating on pte before updating new_pmd
Ack on the concept.
However, not so much on the patch.
Odd whitespace change:
> @@ -254,6 +254,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
> if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
> return false;
> * We don't have to worry about the ordering of src and dst
> * ptlocks because exclusive mmap_lock prevents deadlock.
And new optimization for empty pmd, which seems unrelated to the
change and should presumably be separate:
> @@ -263,6 +264,10 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
> if (new_ptl != old_ptl)
> spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
> + if (pmd_none(*old_pmd))
> + goto unlock_out;
> + pte_ptl = pte_lockptr(mm, old_pmd);
> /* Clear the pmd */
> pmd = *old_pmd;
And also, why does the above assign 'pte_ptl' without using it, when
the actual use is ten lines further down?
So I think this patch needs some cleanup.
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