diff mbox series

[1/5] seccomp: don't use semaphore and wait_queue together

Message ID 20230110213010.2683185-2-avagin@google.com
State New
Headers
Series seccomp: add the synchronous mode for seccomp_unotify |

Commit Message

Andrei Vagin Jan. 10, 2023, 9:30 p.m. UTC 
  From: Andrei Vagin <avagin@gmail.com>

The main reason is to use new wake_up helpers that will be added in the
following patches. But here are a few other reasons:

* if we use two different ways, we always need to call them both. This
  patch fixes seccomp_notify_recv where we forgot to call wake_up_poll
  in the error path.

* If we use one primitive, we can control how many waiters are woken up
  for each request. Our goal is to wake up just one that will handle a
  request. Right now, wake_up_poll can wake up one waiter and
  up(&match->notif->request) can wake up one more.

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 kernel/seccomp.c | 41 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 5 deletions(-)

Comments

Tycho Andersen Jan. 12, 2023, 2:58 p.m. UTC | #1 
On Tue, Jan 10, 2023 at 01:30:06PM -0800, Andrei Vagin wrote:
> From: Andrei Vagin <avagin@gmail.com>
> 
> The main reason is to use new wake_up helpers that will be added in the
> following patches. But here are a few other reasons:
> 
> * if we use two different ways, we always need to call them both. This
>   patch fixes seccomp_notify_recv where we forgot to call wake_up_poll
>   in the error path.

[snip]

> @@ -1515,7 +1546,8 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
>  			if (should_sleep_killable(filter, knotif))
>  				complete(&knotif->ready);
>  			knotif->state = SECCOMP_NOTIFY_INIT;
> -			up(&filter->notif->request);
> +			atomic_add(1, &filter->notif->requests);
> +			wake_up_poll(&filter->wqh, EPOLLIN | EPOLLRDNORM);
>  		}
>  		mutex_unlock(&filter->notify_lock);
>  	}

I wonder if this shouldn't be a separate patch that you can send now
independent of this series?

Tycho
Andrei Vagin Jan. 13, 2023, 9:51 p.m. UTC | #2 
On Thu, Jan 12, 2023 at 6:58 AM Tycho Andersen <tycho@tycho.pizza> wrote:
>
> On Tue, Jan 10, 2023 at 01:30:06PM -0800, Andrei Vagin wrote:
> > From: Andrei Vagin <avagin@gmail.com>
> >
> > The main reason is to use new wake_up helpers that will be added in the
> > following patches. But here are a few other reasons:
> >
> > * if we use two different ways, we always need to call them both. This
> >   patch fixes seccomp_notify_recv where we forgot to call wake_up_poll
> >   in the error path.
>
> [snip]
>
> > @@ -1515,7 +1546,8 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
> >                       if (should_sleep_killable(filter, knotif))
> >                               complete(&knotif->ready);
> >                       knotif->state = SECCOMP_NOTIFY_INIT;
> > -                     up(&filter->notif->request);
> > +                     atomic_add(1, &filter->notif->requests);
> > +                     wake_up_poll(&filter->wqh, EPOLLIN | EPOLLRDNORM);
> >               }
> >               mutex_unlock(&filter->notify_lock);
> >       }
>
> I wonder if this shouldn't be a separate patch that you can send now
> independent of this series?

You are right. It is a bug fix and I can send it in a separate patch.
I didn't expect it would take so long to merge the whole set.

Thanks,
Andrei
Peter Zijlstra Jan. 16, 2023, 9:48 a.m. UTC | #3 
On Tue, Jan 10, 2023 at 01:30:06PM -0800, Andrei Vagin wrote:

> +	atomic_add(1, &match->notif->requests);

atomic_inc() ?
diff mbox series

Patch

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index e9852d1b4a5e..876022e9c88c 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -145,7 +145,7 @@  struct seccomp_kaddfd {
  * @notifications: A list of struct seccomp_knotif elements.
  */
 struct notification {
-	struct semaphore request;
+	atomic_t requests;
 	u64 next_id;
 	struct list_head notifications;
 };
@@ -1116,7 +1116,7 @@  static int seccomp_do_user_notification(int this_syscall,
 	list_add_tail(&n.list, &match->notif->notifications);
 	INIT_LIST_HEAD(&n.addfd);
 
-	up(&match->notif->request);
+	atomic_add(1, &match->notif->requests);
 	wake_up_poll(&match->wqh, EPOLLIN | EPOLLRDNORM);
 
 	/*
@@ -1450,6 +1450,37 @@  find_notification(struct seccomp_filter *filter, u64 id)
 	return NULL;
 }
 
+static int recv_wake_function(wait_queue_entry_t *wait, unsigned int mode, int sync,
+				  void *key)
+{
+	/* Avoid a wakeup if event not interesting for us. */
+	if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))
+		return 0;
+	return autoremove_wake_function(wait, mode, sync, key);
+}
+
+static int recv_wait_event(struct seccomp_filter *filter)
+{
+	DEFINE_WAIT_FUNC(wait, recv_wake_function);
+	int ret;
+
+	if (atomic_add_unless(&filter->notif->requests, -1, 0) != 0)
+		return 0;
+
+	for (;;) {
+		ret = prepare_to_wait_event(&filter->wqh, &wait, TASK_INTERRUPTIBLE);
+
+		if (atomic_add_unless(&filter->notif->requests, -1, 0) != 0)
+			break;
+
+		if (ret)
+			return ret;
+
+		schedule();
+	}
+	finish_wait(&filter->wqh, &wait);
+	return 0;
+}
 
 static long seccomp_notify_recv(struct seccomp_filter *filter,
 				void __user *buf)
@@ -1467,7 +1498,7 @@  static long seccomp_notify_recv(struct seccomp_filter *filter,
 
 	memset(&unotif, 0, sizeof(unotif));
 
-	ret = down_interruptible(&filter->notif->request);
+	ret = recv_wait_event(filter);
 	if (ret < 0)
 		return ret;
 
@@ -1515,7 +1546,8 @@  static long seccomp_notify_recv(struct seccomp_filter *filter,
 			if (should_sleep_killable(filter, knotif))
 				complete(&knotif->ready);
 			knotif->state = SECCOMP_NOTIFY_INIT;
-			up(&filter->notif->request);
+			atomic_add(1, &filter->notif->requests);
+			wake_up_poll(&filter->wqh, EPOLLIN | EPOLLRDNORM);
 		}
 		mutex_unlock(&filter->notify_lock);
 	}
@@ -1777,7 +1809,6 @@  static struct file *init_listener(struct seccomp_filter *filter)
 	if (!filter->notif)
 		goto out;
 
-	sema_init(&filter->notif->request, 0);
 	filter->notif->next_id = get_random_u64();
 	INIT_LIST_HEAD(&filter->notif->notifications);