diff mbox series

[v4,7/7] mm/maps: execute PROCMAP_QUERY ioctl under per-vma locks

Message ID 20250604231151.799834-8-surenb@google.com
State New
Headers show
Series use per-vma locks for /proc/pid/maps reads and PROCMAP_QUERY | expand

Commit Message

Suren Baghdasaryan June 4, 2025, 11:11 p.m. UTC 
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@google.com>
---
 fs/proc/task_mmu.c | 56 ++++++++++++++++++++++++++++++++++++----------
 1 file changed, 44 insertions(+), 12 deletions(-)

Comments

Andrii Nakryiko June 13, 2025, 8:36 p.m. UTC | #1 
On Wed, Jun 4, 2025 at 4:12 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> 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@google.com>
> ---
>  fs/proc/task_mmu.c | 56 ++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 44 insertions(+), 12 deletions(-)
>

The overall approach in this patch set looks good to me! PROCMAP_QUERY
changes specifically are pretty straightforward, nice. LGTM:

Acked-by: Andrii Nakryiko <andrii@kernel.org>

And for the rest of the changes you seem to be in good hands, so I'll
just be waiting for the final thing to land, thanks for working on
this!
diff mbox series

Patch

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 36d883c4f394..93ba35a84975 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -550,28 +550,60 @@  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);
+	rcu_read_lock();
+	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);
+	rcu_read_unlock();
+}
+
+static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_private *priv,
+						     unsigned long addr)
+{
+	vma_iter_init(&priv->iter, priv->mm, addr);
+	return get_next_vma(priv, addr);
+}
+
+#else /* CONFIG_PER_VMA_LOCK */
+
+static int query_vma_setup(struct proc_maps_private *priv)
+{
+	return mmap_read_lock_killable(priv->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 mm_struct *mm, unsigned long addr)
+static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_private *priv,
+						     unsigned long addr)
 {
-	return find_vma(mm, addr);
+	return find_vma(priv->mm, addr);
 }
 
-static struct vm_area_struct *query_matching_vma(struct mm_struct *mm,
+#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;
 
@@ -647,13 +679,13 @@  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;
@@ -738,7 +770,7 @@  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),
@@ -758,7 +790,7 @@  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;