[PATCH v2 1/3] mm: lock a vma before stack expansion

[Suren Baghdasaryan]

With recent changes necessitating mmap_lock to be held for write while
expanding a stack, per-VMA locks should follow the same rules and be
write-locked to prevent page faults into the VMA being expanded. Add
the necessary locking.

Cc: sta...@vger.kernel.org
Signed-off-by: Suren Baghdasaryan <sur...@google.com>
---
 mm/mmap.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 204ddcd52625..c66e4622a557 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1977,6 +1977,8 @@ static int expand_upwards(struct vm_area_struct *vma, 
unsigned long address)
                return -ENOMEM;
        }
 
+       /* Lock the VMA before expanding to prevent concurrent page faults */
+       vma_start_write(vma);
        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
@@ -2064,6 +2066,8 @@ int expand_downwards(struct vm_area_struct *vma, unsigned 
long address)
                return -ENOMEM;
        }
 
+       /* Lock the VMA before expanding to prevent concurrent page faults */
+       vma_start_write(vma);
        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
-- 
2.41.0.390.g38632f3daf-goog