Hi Jann,
On 2024/10/8 05:42, Jann Horn wrote:
[...]
diff --git a/mm/mremap.c b/mm/mremap.c
index 24712f8dbb6b..dda09e957a5d 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -238,6 +238,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
{
spinlock_t *old_ptl, *new_ptl;
struct mm_struct *mm = vma->vm_mm;
+ bool res = false;
pmd_t pmd;
if (!arch_supports_page_table_move())
@@ -277,19 +278,25 @@ 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);
- /* Clear the pmd */
pmd = *old_pmd;
+
+ /* Racing with collapse? */
+ if (unlikely(!pmd_present(pmd) || pmd_leaf(pmd)))
Since we already hold the exclusive mmap lock, after a racing
with collapse occurs, the pmd entry cannot be refilled with
new content by page fault. So maybe we only need to recheck
pmd_none(pmd) here?
Thanks,
Qi
+ goto out_unlock;
+ /* Clear the pmd */
pmd_clear(old_pmd);
+ res = true;
VM_BUG_ON(!pmd_none(*new_pmd));
pmd_populate(mm, new_pmd, pmd_pgtable(pmd));
flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
+out_unlock:
if (new_ptl != old_ptl)
spin_unlock(new_ptl);
spin_unlock(old_ptl);
- return true;
+ return res;
}
#else
static inline bool move_normal_pmd(struct vm_area_struct *vma,
---
base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
change-id: 20241007-move_normal_pmd-vs-collapse-fix-2-387e9a68c7d6
