[PATCH 67/94] fs/userfaultfd: Stop using vma linked list.

[Liam Howlett]

Don't use the mm_struct linked list or the vma->vm_next in prep for removal

Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
 fs/userfaultfd.c | 43 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 36 insertions(+), 7 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 14f92285d04f..1fd0f5b5c934 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -605,14 +605,18 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 	if (release_new_ctx) {
 		struct vm_area_struct *vma;
 		struct mm_struct *mm = release_new_ctx->mm;
+		MA_STATE(mas, &mm->mm_mt, 0, 0);
 
 		/* the various vma->vm_userfaultfd_ctx still points to it */
 		mmap_write_lock(mm);
-		for (vma = mm->mmap; vma; vma = vma->vm_next)
+		mas_lock(&mas);
+		mas_for_each(&mas, vma, ULONG_MAX) {
 			if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
 				vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
 				vma->vm_flags &= ~__VM_UFFD_FLAGS;
 			}
+		}
+		mas_unlock(&mas);
 		mmap_write_unlock(mm);
 
 		userfaultfd_ctx_put(release_new_ctx);
@@ -797,7 +801,10 @@ int userfaultfd_unmap_prep(struct vm_area_struct *vma,
 			   unsigned long start, unsigned long end,
 			   struct list_head *unmaps)
 {
-	for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
+	MA_STATE(mas, &vma->vm_mm->mm_mt, vma->vm_start, vma->vm_start);
+
+	rcu_read_lock();
+	mas_for_each(&mas, vma, end) {
 		struct userfaultfd_unmap_ctx *unmap_ctx;
 		struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
 
@@ -816,6 +823,7 @@ int userfaultfd_unmap_prep(struct vm_area_struct *vma,
 		unmap_ctx->end = end;
 		list_add_tail(&unmap_ctx->list, unmaps);
 	}
+	rcu_read_unlock();
 
 	return 0;
 }
@@ -847,6 +855,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 	/* len == 0 means wake all */
 	struct userfaultfd_wake_range range = { .len = 0, };
 	unsigned long new_flags;
+	MA_STATE(mas, &mm->mm_mt, 0, 0);
 
 	WRITE_ONCE(ctx->released, true);
 
@@ -862,9 +871,14 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 	 * taking the mmap_lock for writing.
 	 */
 	mmap_write_lock(mm);
+	mas_lock(&mas);
 	prev = NULL;
-	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+	mas_for_each(&mas, vma, ULONG_MAX) {
+		mas_unlock(&mas);
+		mas_pause(&mas);
 		cond_resched();
+		mas_lock(&mas);
+
 		BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
 		       !!(vma->vm_flags & __VM_UFFD_FLAGS));
 		if (vma->vm_userfaultfd_ctx.ctx != ctx) {
@@ -884,6 +898,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 		vma->vm_flags = new_flags;
 		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
 	}
+	mas_unlock(&mas);
 	mmap_write_unlock(mm);
 	mmput(mm);
 wakeup:
@@ -1288,6 +1303,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	bool found;
 	bool basic_ioctls;
 	unsigned long start, end, vma_end;
+	MA_STATE(mas, &mm->mm_mt, 0, 0);
 
 	user_uffdio_register = (struct uffdio_register __user *) arg;
 
@@ -1326,6 +1342,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 		goto out;
 
 	mmap_write_lock(mm);
+	rcu_read_lock();
 	vma = find_vma_prev(mm, start, &prev);
 	if (!vma)
 		goto out_unlock;
@@ -1351,8 +1368,12 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	 */
 	found = false;
 	basic_ioctls = false;
-	for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
+	mas_set(&mas, vma->vm_start);
+	mas_for_each(&mas, cur, end) {
+		rcu_read_unlock();
+		mas_pause(&mas);
 		cond_resched();
+		rcu_read_lock();
 
 		BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
 		       !!(cur->vm_flags & __VM_UFFD_FLAGS));
@@ -1469,9 +1490,10 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	skip:
 		prev = vma;
 		start = vma->vm_end;
-		vma = vma->vm_next;
+		vma = vma_next(mm, vma);
 	} while (vma && vma->vm_start < end);
 out_unlock:
+	rcu_read_unlock();
 	mmap_write_unlock(mm);
 	mmput(mm);
 	if (!ret) {
@@ -1514,6 +1536,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 	bool found;
 	unsigned long start, end, vma_end;
 	const void __user *buf = (void __user *)arg;
+	MA_STATE(mas, &mm->mm_mt, 0, 0);
 
 	ret = -EFAULT;
 	if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
@@ -1557,8 +1580,13 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 	 */
 	found = false;
 	ret = -EINVAL;
-	for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
+	rcu_read_lock();
+	mas_set(&mas, vma->vm_start);
+	mas_for_each(&mas, cur, end) {
+		rcu_read_unlock();
+		mas_pause(&mas);
 		cond_resched();
+		rcu_read_lock();
 
 		BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
 		       !!(cur->vm_flags & __VM_UFFD_FLAGS));
@@ -1575,6 +1603,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 
 		found = true;
 	}
+	rcu_read_unlock();
 	BUG_ON(!found);
 
 	if (vma->vm_start < start)
@@ -1643,7 +1672,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 	skip:
 		prev = vma;
 		start = vma->vm_end;
-		vma = vma->vm_next;
+		vma = vma_next(mm, vma);
 	} while (vma && vma->vm_start < end);
 out_unlock:
 	mmap_write_unlock(mm);
-- 
2.30.2