Now that stack growth must always hold the mmap_lock for write, we can
always downgrade the mmap_lock to read and safely unmap pages from the
page table, even if we're next to a stack.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
mm/mmap.c | 15 ++-------------
1 file changed, 2 insertions(+), 13 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 9b5188b65800..82efaca58ca2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2550,19 +2550,8 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
mm->locked_vm -= locked_vm;
mm->map_count -= count;
- /*
- * Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or
- * VM_GROWSUP VMA. Such VMAs can change their size under
- * down_read(mmap_lock) and collide with the VMA we are about to unmap.
- */
- if (downgrade) {
- if (next && (next->vm_flags & VM_GROWSDOWN))
- downgrade = false;
- else if (prev && (prev->vm_flags & VM_GROWSUP))
- downgrade = false;
- else
- mmap_write_downgrade(mm);
- }
+ if (downgrade)
+ mmap_write_downgrade(mm);
/*
* We can free page tables without write-locking mmap_lock because VMAs
--
2.39.2
