[PATCH 0/6 v4] seccomp: add the synchronous mode for seccomp_unotify

[PATCH 0/6 v4] seccomp: add the synchronous mode for seccomp_unotify

[Andrei Vagin]

From: Andrei Vagin <avagin@gmail.com>

seccomp_unotify allows more privileged processes do actions on behalf
of less privileged processes.

In many cases, the workflow is fully synchronous. It means a target
process triggers a system call and passes controls to a supervisor
process that handles the system call and returns controls back to the
target process. In this context, "synchronous" means that only one
process is running and another one is waiting.

The new WF_CURRENT_CPU flag advises the scheduler to move the wakee to
the current CPU. For such synchronous workflows, it makes context
switches a few times faster.

Right now, each interaction takes 12µs. With this patch, it takes about
3µs.

v2: clean up the first patch and add the test.
v3: update commit messages and a few fixes suggested by Kees Cook.
v4: update the third patch to avoid code duplications (suggested by
    Peter Zijlstra)
    Add the benchmark to the perf bench set.

Kees is ready to take this patch set, but wants to get Acks from the
sched folks.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Peter Oskolkov <posk@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tycho Andersen <tycho@tycho.pizza>
Cc: Will Drewry <wad@chromium.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>

Andrei Vagin (4):
  seccomp: don't use semaphore and wait_queue together
  sched: add a few helpers to wake up tasks on the current cpu
  seccomp: add the synchronous mode for seccomp_unotify
  selftest/seccomp: add a new test for the sync mode of
    seccomp_user_notify

Peter Oskolkov (1):
  sched: add WF_CURRENT_CPU and externise ttwu

 include/linux/completion.h                    |   1 +
 include/linux/swait.h                         |   2 +-
 include/linux/wait.h                          |   3 +
 include/uapi/linux/seccomp.h                  |   4 +
 kernel/sched/completion.c                     |  26 ++-
 kernel/sched/core.c                           |   5 +-
 kernel/sched/fair.c                           |   4 +
 kernel/sched/sched.h                          |  13 +-
 kernel/sched/swait.c                          |   8 +-
 kernel/sched/wait.c                           |   5 +
 kernel/seccomp.c                              |  72 +++++++-
 tools/arch/x86/include/uapi/asm/unistd_32.h   |   3 +
 tools/arch/x86/include/uapi/asm/unistd_64.h   |   3 +
 tools/perf/bench/Build                        |   1 +
 tools/perf/bench/bench.h                      |   1 +
 tools/perf/bench/sched-seccomp-notify.c       | 167 ++++++++++++++++++
 tools/perf/builtin-bench.c                    |   1 +
 tools/testing/selftests/seccomp/seccomp_bpf.c |  55 ++++++
 18 files changed, 346 insertions(+), 28 deletions(-)
 create mode 100644 tools/perf/bench/sched-seccomp-notify.c

-- 
2.37.2

[PATCH 1/6] seccomp: don't use semaphore and wait_queue together

[Andrei Vagin]

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(-)

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);
 
-- 
2.39.1.405.gd4c25cc71f-goog

[PATCH 2/6] sched: add WF_CURRENT_CPU and externise ttwu

[Andrei Vagin]

From: Peter Oskolkov <posk@google.com>

Add WF_CURRENT_CPU wake flag that advices the scheduler to
move the wakee to the current CPU. This is useful for fast on-CPU
context switching use cases.

In addition, make ttwu external rather than static so that
the flag could be passed to it from outside of sched/core.c.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 kernel/sched/core.c  |  3 +--
 kernel/sched/fair.c  |  4 ++++
 kernel/sched/sched.h | 13 ++++++++-----
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bb1ee6d7bdde..028c2840baa6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4112,8 +4112,7 @@ bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success)
  * Return: %true if @p->state changes (an actual wakeup was done),
  *	   %false otherwise.
  */
-static int
-try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
+int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 {
 	unsigned long flags;
 	int cpu, success = 0;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c36aa54ae071..d6f76bead3c5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7380,6 +7380,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 	if (wake_flags & WF_TTWU) {
 		record_wakee(p);
 
+		if ((wake_flags & WF_CURRENT_CPU) &&
+		    cpumask_test_cpu(cpu, p->cpus_ptr))
+			return cpu;
+
 		if (sched_energy_enabled()) {
 			new_cpu = find_energy_efficient_cpu(p, prev_cpu);
 			if (new_cpu >= 0)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 771f8ddb7053..34b4c54b2a2a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2088,12 +2088,13 @@ static inline int task_on_rq_migrating(struct task_struct *p)
 }
 
 /* Wake flags. The first three directly map to some SD flag value */
-#define WF_EXEC     0x02 /* Wakeup after exec; maps to SD_BALANCE_EXEC */
-#define WF_FORK     0x04 /* Wakeup after fork; maps to SD_BALANCE_FORK */
-#define WF_TTWU     0x08 /* Wakeup;            maps to SD_BALANCE_WAKE */
+#define WF_EXEC         0x02 /* Wakeup after exec; maps to SD_BALANCE_EXEC */
+#define WF_FORK         0x04 /* Wakeup after fork; maps to SD_BALANCE_FORK */
+#define WF_TTWU         0x08 /* Wakeup;            maps to SD_BALANCE_WAKE */
 
-#define WF_SYNC     0x10 /* Waker goes to sleep after wakeup */
-#define WF_MIGRATED 0x20 /* Internal use, task got migrated */
+#define WF_SYNC         0x10 /* Waker goes to sleep after wakeup */
+#define WF_MIGRATED     0x20 /* Internal use, task got migrated */
+#define WF_CURRENT_CPU  0x40 /* Prefer to move the wakee to the current CPU. */
 
 #ifdef CONFIG_SMP
 static_assert(WF_EXEC == SD_BALANCE_EXEC);
@@ -3245,6 +3246,8 @@ static inline bool is_per_cpu_kthread(struct task_struct *p)
 extern void swake_up_all_locked(struct swait_queue_head *q);
 extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
 
+extern int try_to_wake_up(struct task_struct *tsk, unsigned int state, int wake_flags);
+
 #ifdef CONFIG_PREEMPT_DYNAMIC
 extern int preempt_dynamic_mode;
 extern int sched_dynamic_mode(const char *str);
-- 
2.39.1.405.gd4c25cc71f-goog

[PATCH 3/6] sched: add a few helpers to wake up tasks on the current cpu

[Andrei Vagin]

From: Andrei Vagin <avagin@gmail.com>

Add complete_on_current_cpu, wake_up_poll_on_current_cpu helpers to wake
up tasks on the current CPU.

These two helpers are useful when the task needs to make a synchronous context
switch to another task. In this context, synchronous means it wakes up the
target task and falls asleep right after that.

One example of such workloads is seccomp user notifies. This mechanism allows
the  supervisor process handles system calls on behalf of a target process.
While the supervisor is handling an intercepted system call, the target process
will be blocked in the kernel, waiting for a response to come back.

On-CPU context switches are much faster than regular ones.

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 include/linux/completion.h |  1 +
 include/linux/swait.h      |  2 +-
 include/linux/wait.h       |  3 +++
 kernel/sched/completion.c  | 26 ++++++++++++++++++--------
 kernel/sched/core.c        |  2 +-
 kernel/sched/swait.c       |  8 ++++----
 kernel/sched/wait.c        |  5 +++++
 7 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/include/linux/completion.h b/include/linux/completion.h
index 62b32b19e0a8..fb2915676574 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -116,6 +116,7 @@ extern bool try_wait_for_completion(struct completion *x);
 extern bool completion_done(struct completion *x);
 
 extern void complete(struct completion *);
+extern void complete_on_current_cpu(struct completion *x);
 extern void complete_all(struct completion *);
 
 #endif
diff --git a/include/linux/swait.h b/include/linux/swait.h
index 6a8c22b8c2a5..d324419482a0 100644
--- a/include/linux/swait.h
+++ b/include/linux/swait.h
@@ -146,7 +146,7 @@ static inline bool swq_has_sleeper(struct swait_queue_head *wq)
 
 extern void swake_up_one(struct swait_queue_head *q);
 extern void swake_up_all(struct swait_queue_head *q);
-extern void swake_up_locked(struct swait_queue_head *q);
+extern void swake_up_locked(struct swait_queue_head *q, int wake_flags);
 
 extern void prepare_to_swait_exclusive(struct swait_queue_head *q, struct swait_queue *wait, int state);
 extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);
diff --git a/include/linux/wait.h b/include/linux/wait.h
index a0307b516b09..5ec7739400f4 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -210,6 +210,7 @@ __remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq
 }
 
 int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
+void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key);
 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key);
 void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
 		unsigned int mode, void *key, wait_queue_entry_t *bookmark);
@@ -237,6 +238,8 @@ void __wake_up_pollfree(struct wait_queue_head *wq_head);
 #define key_to_poll(m) ((__force __poll_t)(uintptr_t)(void *)(m))
 #define wake_up_poll(x, m)							\
 	__wake_up(x, TASK_NORMAL, 1, poll_to_key(m))
+#define wake_up_poll_on_current_cpu(x, m)					\
+	__wake_up_on_current_cpu(x, TASK_NORMAL, poll_to_key(m))
 #define wake_up_locked_poll(x, m)						\
 	__wake_up_locked_key((x), TASK_NORMAL, poll_to_key(m))
 #define wake_up_interruptible_poll(x, m)					\
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index d57a5c1c1cd9..3561ab533dd4 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -13,6 +13,23 @@
  * Waiting for completion is a typically sync point, but not an exclusion point.
  */
 
+static void complete_with_flags(struct completion *x, int wake_flags)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&x->wait.lock, flags);
+
+	if (x->done != UINT_MAX)
+		x->done++;
+	swake_up_locked(&x->wait, wake_flags);
+	raw_spin_unlock_irqrestore(&x->wait.lock, flags);
+}
+
+void complete_on_current_cpu(struct completion *x)
+{
+	return complete_with_flags(x, WF_CURRENT_CPU);
+}
+
 /**
  * complete: - signals a single thread waiting on this completion
  * @x:  holds the state of this particular completion
@@ -27,14 +44,7 @@
  */
 void complete(struct completion *x)
 {
-	unsigned long flags;
-
-	raw_spin_lock_irqsave(&x->wait.lock, flags);
-
-	if (x->done != UINT_MAX)
-		x->done++;
-	swake_up_locked(&x->wait);
-	raw_spin_unlock_irqrestore(&x->wait.lock, flags);
+	complete_with_flags(x, 0);
 }
 EXPORT_SYMBOL(complete);
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 028c2840baa6..a4cb1b5fd52d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6925,7 +6925,7 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
 int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
 			  void *key)
 {
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~WF_SYNC);
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~(WF_SYNC|WF_CURRENT_CPU));
 	return try_to_wake_up(curr->private, mode, wake_flags);
 }
 EXPORT_SYMBOL(default_wake_function);
diff --git a/kernel/sched/swait.c b/kernel/sched/swait.c
index 76b9b796e695..72505cd3b60a 100644
--- a/kernel/sched/swait.c
+++ b/kernel/sched/swait.c
@@ -18,7 +18,7 @@ EXPORT_SYMBOL(__init_swait_queue_head);
  * If for some reason it would return 0, that means the previously waiting
  * task is already running, so it will observe condition true (or has already).
  */
-void swake_up_locked(struct swait_queue_head *q)
+void swake_up_locked(struct swait_queue_head *q, int wake_flags)
 {
 	struct swait_queue *curr;
 
@@ -26,7 +26,7 @@ void swake_up_locked(struct swait_queue_head *q)
 		return;
 
 	curr = list_first_entry(&q->task_list, typeof(*curr), task_list);
-	wake_up_process(curr->task);
+	try_to_wake_up(curr->task, TASK_NORMAL, wake_flags);
 	list_del_init(&curr->task_list);
 }
 EXPORT_SYMBOL(swake_up_locked);
@@ -41,7 +41,7 @@ EXPORT_SYMBOL(swake_up_locked);
 void swake_up_all_locked(struct swait_queue_head *q)
 {
 	while (!list_empty(&q->task_list))
-		swake_up_locked(q);
+		swake_up_locked(q, 0);
 }
 
 void swake_up_one(struct swait_queue_head *q)
@@ -49,7 +49,7 @@ void swake_up_one(struct swait_queue_head *q)
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&q->lock, flags);
-	swake_up_locked(q);
+	swake_up_locked(q, 0);
 	raw_spin_unlock_irqrestore(&q->lock, flags);
 }
 EXPORT_SYMBOL(swake_up_one);
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 133b74730738..47803a0b8d5d 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -161,6 +161,11 @@ int __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
 }
 EXPORT_SYMBOL(__wake_up);
 
+void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key)
+{
+	__wake_up_common_lock(wq_head, mode, 1, WF_CURRENT_CPU, key);
+}
+
 /*
  * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
  */
-- 
2.39.1.405.gd4c25cc71f-goog

[PATCH 4/6] seccomp: add the synchronous mode for seccomp_unotify

[Andrei Vagin]

From: Andrei Vagin <avagin@gmail.com>

seccomp_unotify allows more privileged processes do actions on behalf
of less privileged processes.

In many cases, the workflow is fully synchronous. It means a target
process triggers a system call and passes controls to a supervisor
process that handles the system call and returns controls to the target
process. In this context, "synchronous" means that only one process is
running and another one is waiting.

There is the WF_CURRENT_CPU flag that is used to advise the scheduler to
move the wakee to the current CPU. For such synchronous workflows, it
makes context switches a few times faster.

Right now, each interaction takes 12µs. With this patch, it takes about
3µs.

This change introduce the SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP flag that
it used to enable the sync mode.

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 include/uapi/linux/seccomp.h |  4 ++++
 kernel/seccomp.c             | 31 +++++++++++++++++++++++++++++--
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index 0fdc6ef02b94..dbfc9b37fcae 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h
@@ -115,6 +115,8 @@ struct seccomp_notif_resp {
 	__u32 flags;
 };
 
+#define SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP (1UL << 0)
+
 /* valid flags for seccomp_notif_addfd */
 #define SECCOMP_ADDFD_FLAG_SETFD	(1UL << 0) /* Specify remote fd */
 #define SECCOMP_ADDFD_FLAG_SEND		(1UL << 1) /* Addfd and return it, atomically */
@@ -150,4 +152,6 @@ struct seccomp_notif_addfd {
 #define SECCOMP_IOCTL_NOTIF_ADDFD	SECCOMP_IOW(3, \
 						struct seccomp_notif_addfd)
 
+#define SECCOMP_IOCTL_NOTIF_SET_FLAGS	SECCOMP_IOW(4, __u64)
+
 #endif /* _UAPI_LINUX_SECCOMP_H */
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 876022e9c88c..0a62d44f4898 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -143,9 +143,12 @@ struct seccomp_kaddfd {
  *           filter->notify_lock.
  * @next_id: The id of the next request.
  * @notifications: A list of struct seccomp_knotif elements.
+ * @flags: A set of SECCOMP_USER_NOTIF_FD_* flags.
  */
+
 struct notification {
 	atomic_t requests;
+	u32 flags;
 	u64 next_id;
 	struct list_head notifications;
 };
@@ -1117,7 +1120,10 @@ static int seccomp_do_user_notification(int this_syscall,
 	INIT_LIST_HEAD(&n.addfd);
 
 	atomic_add(1, &match->notif->requests);
-	wake_up_poll(&match->wqh, EPOLLIN | EPOLLRDNORM);
+	if (match->notif->flags & SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP)
+		wake_up_poll_on_current_cpu(&match->wqh, EPOLLIN | EPOLLRDNORM);
+	else
+		wake_up_poll(&match->wqh, EPOLLIN | EPOLLRDNORM);
 
 	/*
 	 * This is where we wait for a reply from userspace.
@@ -1593,7 +1599,10 @@ static long seccomp_notify_send(struct seccomp_filter *filter,
 	knotif->error = resp.error;
 	knotif->val = resp.val;
 	knotif->flags = resp.flags;
-	complete(&knotif->ready);
+	if (filter->notif->flags & SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP)
+		complete_on_current_cpu(&knotif->ready);
+	else
+		complete(&knotif->ready);
 out:
 	mutex_unlock(&filter->notify_lock);
 	return ret;
@@ -1623,6 +1632,22 @@ static long seccomp_notify_id_valid(struct seccomp_filter *filter,
 	return ret;
 }
 
+static long seccomp_notify_set_flags(struct seccomp_filter *filter,
+				    unsigned long flags)
+{
+	long ret;
+
+	if (flags & ~SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP)
+		return -EINVAL;
+
+	ret = mutex_lock_interruptible(&filter->notify_lock);
+	if (ret < 0)
+		return ret;
+	filter->notif->flags = flags;
+	mutex_unlock(&filter->notify_lock);
+	return 0;
+}
+
 static long seccomp_notify_addfd(struct seccomp_filter *filter,
 				 struct seccomp_notif_addfd __user *uaddfd,
 				 unsigned int size)
@@ -1752,6 +1777,8 @@ static long seccomp_notify_ioctl(struct file *file, unsigned int cmd,
 	case SECCOMP_IOCTL_NOTIF_ID_VALID_WRONG_DIR:
 	case SECCOMP_IOCTL_NOTIF_ID_VALID:
 		return seccomp_notify_id_valid(filter, buf);
+	case SECCOMP_IOCTL_NOTIF_SET_FLAGS:
+		return seccomp_notify_set_flags(filter, arg);
 	}
 
 	/* Extensible Argument ioctls */
-- 
2.39.1.405.gd4c25cc71f-goog

[PATCH 5/6] selftest/seccomp: add a new test for the sync mode of seccomp_user_notify

[Andrei Vagin]

From: Andrei Vagin <avagin@gmail.com>

Test output:
 #  RUN           global.user_notification_sync ...
 #            OK  global.user_notification_sync
 ok 51 global.user_notification_sync

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 55 +++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 9c2f448bb3a9..05b8de6d1fcb 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -4243,6 +4243,61 @@ TEST(user_notification_addfd_rlimit)
 	close(memfd);
 }
 
+#ifndef SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP
+#define SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP (1UL << 0)
+#define SECCOMP_IOCTL_NOTIF_SET_FLAGS  SECCOMP_IOW(4, __u64)
+#endif
+
+TEST(user_notification_sync)
+{
+	struct seccomp_notif req = {};
+	struct seccomp_notif_resp resp = {};
+	int status, listener;
+	pid_t pid;
+	long ret;
+
+	ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+	ASSERT_EQ(0, ret) {
+		TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
+	}
+
+	listener = user_notif_syscall(__NR_getppid,
+				      SECCOMP_FILTER_FLAG_NEW_LISTENER);
+	ASSERT_GE(listener, 0);
+
+	/* Try to set invalid flags. */
+	EXPECT_SYSCALL_RETURN(-EINVAL,
+		ioctl(listener, SECCOMP_IOCTL_NOTIF_SET_FLAGS, 0xffffffff, 0));
+
+	ASSERT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SET_FLAGS,
+			SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP, 0), 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+	if (pid == 0) {
+		ret = syscall(__NR_getppid);
+		ASSERT_EQ(ret, USER_NOTIF_MAGIC) {
+			_exit(1);
+		}
+		_exit(0);
+	}
+
+	req.pid = 0;
+	ASSERT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+
+	ASSERT_EQ(req.data.nr,  __NR_getppid);
+
+	resp.id = req.id;
+	resp.error = 0;
+	resp.val = USER_NOTIF_MAGIC;
+	resp.flags = 0;
+	ASSERT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0);
+
+	ASSERT_EQ(waitpid(pid, &status, 0), pid);
+	ASSERT_EQ(status, 0);
+}
+
+
 /* Make sure PTRACE_O_SUSPEND_SECCOMP requires CAP_SYS_ADMIN. */
 FIXTURE(O_SUSPEND_SECCOMP) {
 	pid_t pid;
-- 
2.39.1.405.gd4c25cc71f-goog

[PATCH 6/6] perf/benchmark: add a new benchmark for seccom_unotify

[Andrei Vagin]

From: Andrei Vagin <avagin@gmail.com>

The benchmark is similar to the pipe benchmark. It creates two processes,
one is calling syscalls, and another process is handling them via seccomp
user notifications. It measures the time required to run a specified number
of interations.

 $ ./perf bench sched  seccomp-notify --sync-mode --loop 1000000
 # Running 'sched/seccomp-notify' benchmark:
 # Executed 1000000 system calls

     Total time: 2.769 [sec]

       2.769629 usecs/op
         361059 ops/sec

 $ ./perf bench sched  seccomp-notify
 # Running 'sched/seccomp-notify' benchmark:
 # Executed 1000000 system calls

     Total time: 8.571 [sec]

       8.571119 usecs/op
         116670 ops/sec

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 tools/arch/x86/include/uapi/asm/unistd_32.h |   3 +
 tools/arch/x86/include/uapi/asm/unistd_64.h |   3 +
 tools/perf/bench/Build                      |   1 +
 tools/perf/bench/bench.h                    |   1 +
 tools/perf/bench/sched-seccomp-notify.c     | 167 ++++++++++++++++++++
 tools/perf/builtin-bench.c                  |   1 +
 6 files changed, 176 insertions(+)
 create mode 100644 tools/perf/bench/sched-seccomp-notify.c

diff --git a/tools/arch/x86/include/uapi/asm/unistd_32.h b/tools/arch/x86/include/uapi/asm/unistd_32.h
index 60a89dba01b6..c0c74befc8df 100644
--- a/tools/arch/x86/include/uapi/asm/unistd_32.h
+++ b/tools/arch/x86/include/uapi/asm/unistd_32.h
@@ -14,3 +14,6 @@
 #ifndef __NR_setns
 # define __NR_setns 346
 #endif
+#ifdef __NR_seccomp
+#define __NR_seccomp 354
+#endif
diff --git a/tools/arch/x86/include/uapi/asm/unistd_64.h b/tools/arch/x86/include/uapi/asm/unistd_64.h
index cb52a3a8b8fc..b695246da684 100644
--- a/tools/arch/x86/include/uapi/asm/unistd_64.h
+++ b/tools/arch/x86/include/uapi/asm/unistd_64.h
@@ -14,3 +14,6 @@
 #ifndef __NR_setns
 #define __NR_setns 308
 #endif
+#ifndef __NR_seccomp
+#define __NR_seccomp 317
+#endif
diff --git a/tools/perf/bench/Build b/tools/perf/bench/Build
index 6b6155a8ad09..e3ec2c1b0682 100644
--- a/tools/perf/bench/Build
+++ b/tools/perf/bench/Build
@@ -1,5 +1,6 @@
 perf-y += sched-messaging.o
 perf-y += sched-pipe.o
+perf-y += sched-seccomp-notify.o
 perf-y += syscall.o
 perf-y += mem-functions.o
 perf-y += futex-hash.o
diff --git a/tools/perf/bench/bench.h b/tools/perf/bench/bench.h
index a5d49b3b6a09..40657b0959a9 100644
--- a/tools/perf/bench/bench.h
+++ b/tools/perf/bench/bench.h
@@ -21,6 +21,7 @@ extern struct timeval bench__start, bench__end, bench__runtime;
 int bench_numa(int argc, const char **argv);
 int bench_sched_messaging(int argc, const char **argv);
 int bench_sched_pipe(int argc, const char **argv);
+int bench_sched_seccomp_notify(int argc, const char **argv);
 int bench_syscall_basic(int argc, const char **argv);
 int bench_mem_memcpy(int argc, const char **argv);
 int bench_mem_memset(int argc, const char **argv);
diff --git a/tools/perf/bench/sched-seccomp-notify.c b/tools/perf/bench/sched-seccomp-notify.c
new file mode 100644
index 000000000000..f6f32b0a865a
--- /dev/null
+++ b/tools/perf/bench/sched-seccomp-notify.c
@@ -0,0 +1,167 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <subcmd/parse-options.h>
+#include "bench.h"
+
+#include <uapi/linux/filter.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <linux/unistd.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <linux/time64.h>
+#include <linux/seccomp.h>
+#include <sys/prctl.h>
+
+#include <unistd.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <string.h>
+#include <errno.h>
+#include <assert.h>
+
+#define LOOPS_DEFAULT 1000000UL
+static uint64_t		loops = LOOPS_DEFAULT;
+static bool sync_mode;
+static const struct option options[] = {
+	OPT_U64('l', "loop",	&loops,		"Specify number of loops"),
+	OPT_BOOLEAN('s', "sync-mode", &sync_mode,
+		    "Enable the synchronious mode for seccomp notifications"),
+	OPT_END()
+};
+
+static const char * const bench_seccomp_usage[] = {
+	"perf bench sched secccomp-notify <options>",
+	NULL
+};
+
+static int seccomp(unsigned int op, unsigned int flags, void *args)
+{
+	return syscall(__NR_seccomp, op, flags, args);
+}
+
+static int user_notif_syscall(int nr, unsigned int flags)
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
+			offsetof(struct seccomp_data, nr)),
+		BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, nr, 0, 1),
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_USER_NOTIF),
+		BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+	};
+
+	struct sock_fprog prog = {
+		.len = (unsigned short)ARRAY_SIZE(filter),
+		.filter = filter,
+	};
+
+	return seccomp(SECCOMP_SET_MODE_FILTER, flags, &prog);
+}
+
+#define USER_NOTIF_MAGIC INT_MAX
+static void user_notification_sync_loop(int listener)
+{
+	struct seccomp_notif_resp resp;
+	struct seccomp_notif req;
+	uint64_t nr;
+
+	for (nr = 0; nr < loops; nr++) {
+		memset(&req, 0, sizeof(req));
+		assert(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req) == 0);
+
+		assert(req.data.nr == __NR_gettid);
+
+		resp.id = req.id;
+		resp.error = 0;
+		resp.val = USER_NOTIF_MAGIC;
+		resp.flags = 0;
+		assert(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp) == 0);
+	}
+}
+
+#ifndef SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP
+#define SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP (1UL << 0)
+#define SECCOMP_IOCTL_NOTIF_SET_FLAGS  SECCOMP_IOW(4, __u64)
+#endif
+int bench_sched_seccomp_notify(int argc, const char **argv)
+{
+	struct timeval start, stop, diff;
+	unsigned long long result_usec = 0;
+	int status, listener;
+	pid_t pid;
+	long ret;
+
+	argc = parse_options(argc, argv, options, bench_seccomp_usage, 0);
+
+	gettimeofday(&start, NULL);
+
+	prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+	listener = user_notif_syscall(__NR_gettid,
+				      SECCOMP_FILTER_FLAG_NEW_LISTENER);
+	assert(listener >= 0);
+
+	pid = fork();
+	assert(pid >= 0);
+	if (pid == 0) {
+		assert(prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0) == 0);
+		while (1) {
+			ret = syscall(__NR_gettid);
+			if (ret == USER_NOTIF_MAGIC)
+				continue;
+			break;
+		}
+		_exit(1);
+	}
+
+	if (sync_mode) {
+		assert(ioctl(listener, SECCOMP_IOCTL_NOTIF_SET_FLAGS,
+			     SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP, 0) == 0);
+	}
+	user_notification_sync_loop(listener);
+
+	kill(pid, SIGKILL);
+	assert(waitpid(pid, &status, 0) == pid);
+	assert(WIFSIGNALED(status));
+	assert(WTERMSIG(status) == SIGKILL);
+
+	gettimeofday(&stop, NULL);
+	timersub(&stop, &start, &diff);
+
+	switch (bench_format) {
+	case BENCH_FORMAT_DEFAULT:
+		printf("# Executed %lu system calls\n\n",
+			loops);
+
+		result_usec = diff.tv_sec * USEC_PER_SEC;
+		result_usec += diff.tv_usec;
+
+		printf(" %14s: %lu.%03lu [sec]\n\n", "Total time",
+		       (unsigned long) diff.tv_sec,
+		       (unsigned long) (diff.tv_usec / USEC_PER_MSEC));
+
+		printf(" %14lf usecs/op\n",
+		       (double)result_usec / (double)loops);
+		printf(" %14d ops/sec\n",
+		       (int)((double)loops /
+			     ((double)result_usec / (double)USEC_PER_SEC)));
+		break;
+
+	case BENCH_FORMAT_SIMPLE:
+		printf("%lu.%03lu\n",
+		       (unsigned long) diff.tv_sec,
+		       (unsigned long) (diff.tv_usec / USEC_PER_MSEC));
+		break;
+
+	default:
+		/* reaching here is something disaster */
+		fprintf(stderr, "Unknown format:%d\n", bench_format);
+		exit(1);
+		break;
+	}
+
+	return 0;
+}
diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index 334ab897aae3..71044575c571 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -46,6 +46,7 @@ static struct bench numa_benchmarks[] = {
 static struct bench sched_benchmarks[] = {
 	{ "messaging",	"Benchmark for scheduling and IPC",		bench_sched_messaging	},
 	{ "pipe",	"Benchmark for pipe() between two processes",	bench_sched_pipe	},
+	{ "seccomp-notify",	"Benchmark for seccomp user notify",	bench_sched_seccomp_notify},
 	{ "all",	"Run all scheduler benchmarks",		NULL			},
 	{ NULL,		NULL,						NULL			}
 };
-- 
2.39.1.405.gd4c25cc71f-goog

Re: [PATCH 0/6 v4] seccomp: add the synchronous mode for seccomp_unotify

[Sean Christopherson]

On Tue, Jan 24, 2023, Andrei Vagin wrote:
> From: Andrei Vagin <avagin@gmail.com>

Is attributing your personal email intentional, or is user.email in your git config
misconfigured?  Quite a few folks use non-corp accounts, but I don't think I've
ever seen a case where someone intentionally posts from their corp email on behalf
of a personal account.

I don't mean to be the SoB police, this just stood out as being very odd.

Re: [PATCH 0/6 v4] seccomp: add the synchronous mode for seccomp_unotify

[Andrei Vagin]

On Wed, Jan 25, 2023 at 9:46 AM Sean Christopherson <seanjc@google.com> wrote:
>
> On Tue, Jan 24, 2023, Andrei Vagin wrote:
> > From: Andrei Vagin <avagin@gmail.com>
>
> Is attributing your personal email intentional, or is user.email in your git config
> misconfigured?  Quite a few folks use non-corp accounts, but I don't think I've
> ever seen a case where someone intentionally posts from their corp email on behalf
> of a personal account.
>
> I don't mean to be the SoB police, this just stood out as being very odd.

I was more often working on kernel changes unrelated to my work at
Google. They were around the CRIU project. It is why I used my personal
email in the kernel git config. I will fix that.

Thanks,
Andrei

[PATCH 1/6] seccomp: don't use semaphore and wait_queue together

[Andrei Vagin]

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@google.com>
---
 kernel/seccomp.c | 41 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index cebf26445f9e..9fca9345111c 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_inc(&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_dec_if_positive(&filter->notif->requests) >= 0)
+		return 0;
+
+	for (;;) {
+		ret = prepare_to_wait_event(&filter->wqh, &wait, TASK_INTERRUPTIBLE);
+
+		if (atomic_dec_if_positive(&filter->notif->requests) >= 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_inc(&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);
 
-- 
2.40.0.rc0.216.gc4246ad0f0-goog

[PATCH 1/6] seccomp: don't use semaphore and wait_queue together

[Andrei Vagin]

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@google.com>
---
 kernel/seccomp.c | 41 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 5 deletions(-)

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);
 
-- 
2.39.1.456.gfc5497dd1b-goog