1 files changed, 18 insertions, 11 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 79d851be8ab2..b5f72ce569e6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3214,6 +3214,21 @@ static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
 	return VM_FAULT_RETRY;
 }
 
+/**
+ * vmf_anon_prepare - Prepare to handle an anonymous fault.
+ * @vmf: The vm_fault descriptor passed from the fault handler.
+ *
+ * When preparing to insert an anonymous page into a VMA from a
+ * fault handler, call this function rather than anon_vma_prepare().
+ * If this vma does not already have an associated anon_vma and we are
+ * only protected by the per-VMA lock, the caller must retry with the
+ * mmap_lock held.  __anon_vma_prepare() will look at adjacent VMAs to
+ * determine if this VMA can share its anon_vma, and that's not safe to
+ * do with only the per-VMA lock held for this VMA.
+ *
+ * Return: 0 if fault handling can proceed.  Any other value should be
+ * returned to the caller.
+ */
 vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
@@ -4439,8 +4454,9 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	}
 
 	/* Allocate our own private page. */
-	if (unlikely(anon_vma_prepare(vma)))
-		goto oom;
+	ret = vmf_anon_prepare(vmf);
+	if (ret)
+		return ret;
 	/* Returns NULL on OOM or ERR_PTR(-EAGAIN) if we must retry the fault */
 	folio = alloc_anon_folio(vmf);
 	if (IS_ERR(folio))
@@ -5828,15 +5844,6 @@ retry:
 	if (!vma_start_read(vma))
 		goto inval;
 
-	/*
-	 * find_mergeable_anon_vma uses adjacent vmas which are not locked.
-	 * This check must happen after vma_start_read(); otherwise, a
-	 * concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA
-	 * from its anon_vma.
-	 */
-	if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma))
-		goto inval_end_read;
-
 	/* Check since vm_start/vm_end might change before we lock the VMA */
 	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
 		goto inval_end_read;