[PATCH v6 8/8] fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks

[Suren Baghdasaryan]

Utilize per-vma locks to stabilize vma after lookup without taking
mmap_lock during PROCMAP_QUERY ioctl execution. While we might take
mmap_lock for reading during contention, we do that momentarily only
to lock the vma.
This change is designed to reduce mmap_lock contention and prevent
PROCMAP_QUERY ioctl calls from blocking address space updates.

Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
 fs/proc/task_mmu.c | 60 ++++++++++++++++++++++++++++++++++++----------
 1 file changed, 48 insertions(+), 12 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ff3fe488ce51..0496d5969a51 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -487,28 +487,64 @@ static int pid_maps_open(struct inode *inode, struct file *file)
 		PROCMAP_QUERY_VMA_FLAGS				\
 )
 
-static int query_vma_setup(struct mm_struct *mm)
+#ifdef CONFIG_PER_VMA_LOCK
+
+static int query_vma_setup(struct proc_maps_private *priv)
 {
-	return mmap_read_lock_killable(mm);
+	priv->locked_vma = NULL;
+	priv->mmap_locked = false;
+
+	return 0;
 }
 
-static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct *vma)
+static void query_vma_teardown(struct proc_maps_private *priv)
 {
-	mmap_read_unlock(mm);
+	unlock_vma(priv);
+}
+
+static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_private *priv,
+						     unsigned long addr)
+{
+	struct vm_area_struct *vma;
+
+	rcu_read_lock();
+	vma_iter_init(&priv->iter, priv->mm, addr);
+	vma = get_next_vma(priv, addr);
+	rcu_read_unlock();
+
+	return vma;
 }
 
-static struct vm_area_struct *query_vma_find_by_addr(struct mm_struct *mm, unsigned long addr)
+#else /* CONFIG_PER_VMA_LOCK */
+
+static int query_vma_setup(struct proc_maps_private *priv)
 {
-	return find_vma(mm, addr);
+	return mmap_read_lock_killable(priv->mm);
 }
 
-static struct vm_area_struct *query_matching_vma(struct mm_struct *mm,
+static void query_vma_teardown(struct proc_maps_private *priv)
+{
+	mmap_read_unlock(priv->mm);
+}
+
+static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_private *priv,
+						     unsigned long addr)
+{
+	return find_vma(priv->mm, addr);
+}
+
+#endif  /* CONFIG_PER_VMA_LOCK */
+
+static struct vm_area_struct *query_matching_vma(struct proc_maps_private *priv,
 						 unsigned long addr, u32 flags)
 {
 	struct vm_area_struct *vma;
 
 next_vma:
-	vma = query_vma_find_by_addr(mm, addr);
+	vma = query_vma_find_by_addr(priv, addr);
+	if (IS_ERR(vma))
+		return vma;
+
 	if (!vma)
 		goto no_vma;
 
@@ -584,13 +620,13 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
 	if (!mm || !mmget_not_zero(mm))
 		return -ESRCH;
 
-	err = query_vma_setup(mm);
+	err = query_vma_setup(priv);
 	if (err) {
 		mmput(mm);
 		return err;
 	}
 
-	vma = query_matching_vma(mm, karg.query_addr, karg.query_flags);
+	vma = query_matching_vma(priv, karg.query_addr, karg.query_flags);
 	if (IS_ERR(vma)) {
 		err = PTR_ERR(vma);
 		vma = NULL;
@@ -675,7 +711,7 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
 	}
 
 	/* unlock vma or mmap_lock, and put mm_struct before copying data to user */
-	query_vma_teardown(mm, vma);
+	query_vma_teardown(priv);
 	mmput(mm);
 
 	if (karg.vma_name_size && copy_to_user(u64_to_user_ptr(karg.vma_name_addr),
@@ -695,7 +731,7 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
 	return 0;
 
 out:
-	query_vma_teardown(mm, vma);
+	query_vma_teardown(priv);
 	mmput(mm);
 	kfree(name_buf);
 	return err;
-- 
2.50.0.727.gbf7dc18ff4-goog