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

Commit Message

Suren Baghdasaryan July 8, 2023, 7:12 p.m. UTC

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: [e-mail]
Signed-off-by: Suren Baghdasaryan <[e-mail]>
---
 mm/mmap.c | 4 ++++
 1 file changed, 4 insertions(+)

Patch

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