Merge tag 'v5.4.57' into dev-5.4dev-5.4

This is the 5.4.57 stable release

Signed-off-by: Joel Stanley <joel@jms.id.au>

1 files changed, 14 insertions, 2 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 514cc19c5916..ea1ba2db4f4f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2622,7 +2622,7 @@ 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)
 {
@@ -2647,6 +2647,17 @@ 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;
 }
 
 /*
@@ -2827,7 +2838,8 @@ 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)
 		downgrade_write(&mm->mmap_sem);