[PATCH v2 2/9] mm: Allow per-VMA locks on file-backed VMAs

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

The fault path will immediately fail in handle_mm_fault(), so this
is the minimal step which allows the per-VMA lock to be taken on
file-backed VMAs.  There may be a small performance reduction as a
little unnecessary work will be done on each page fault.  See later
patches for the improvement.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/memory.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 2c7967632866..f2dcc695f54e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5247,6 +5247,11 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 		goto out;
 	}
 
+	if ((flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vma)) {
+		vma_end_read(vma);
+		return VM_FAULT_RETRY;
+	}
+
 	/*
 	 * Enable the memcg OOM handling for faults triggered in user
 	 * space.  Kernel faults are handled more gracefully.
@@ -5418,12 +5423,8 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	if (!vma)
 		goto inval;
 
-	/* Only anonymous vmas are supported for now */
-	if (!vma_is_anonymous(vma))
-		goto inval;
-
 	/* find_mergeable_anon_vma uses adjacent vmas which are not locked */
-	if (!vma->anon_vma)
+	if (vma_is_anonymous(vma) && !vma->anon_vma)
 		goto inval;
 
 	if (!vma_start_read(vma))
-- 
2.39.2