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-rw-r--r--mm/mmap.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index 59a4682ebf3f..8c7ca737a19b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2620,7 +2620,7 @@ static void unmap_region(struct mm_struct *mm,
* Create a list of vma's touched by the unmap, removing them from the mm's
* vma list as we go..
*/
-static void
+static bool
detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
struct vm_area_struct *prev, unsigned long end)
{
@@ -2645,6 +2645,17 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
/* Kill the cache */
vmacache_invalidate(mm);
+
+ /*
+ * 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 (vma && (vma->vm_flags & VM_GROWSDOWN))
+ return false;
+ if (prev && (prev->vm_flags & VM_GROWSUP))
+ return false;
+ return true;
}
/*
@@ -2825,7 +2836,8 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
}
/* Detach vmas from rbtree */
- detach_vmas_to_be_unmapped(mm, vma, prev, end);
+ if (!detach_vmas_to_be_unmapped(mm, vma, prev, end))
+ downgrade = false;
if (downgrade)
mmap_write_downgrade(mm);