kernfs: Improve kernfs_notify() poll notification latency (03c0a920) · Commits · 戴 / test

kernfs_notify() does two notifications: poll and fsnotify. Originally, both notifications were done from scheduled work context and all that kernfs_notify() did was schedule the work. This patch simply moves the poll notification from the scheduled work handler to kernfs_notify(). The fsnotify notification still needs to be done from scheduled work context because it can sleep (it needs to lock a mutex). If the poll notification is time critical (the notified thread needs to wake as quickly as possible), it's better to do it from kernfs_notify() directly. One example is calling sysfs_notify_dirent() from a hardware interrupt handler to wake up a thread and handle the interrupt in user space. Signed-off-by:

Radu Rendec <radu.rendec@gmail.com> Acked-by:

Tejun Heo <tj@kernel.org> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/kernfs/file.c

+11 −12

Original line number	Diff line number	Diff line
		@@ -857,7 +857,6 @@ static __poll_t kernfs_fop_poll(struct file filp, poll_table wait)
		static void kernfs_notify_workfn(struct work_struct *work)
		{
		struct kernfs_node *kn;
		struct kernfs_open_node *on;
		struct kernfs_super_info *info;
		repeat:
		/* pop one off the notify_list */
		@@ -871,17 +870,6 @@ repeat:
		kn->attr.notify_next = NULL;
		spin_unlock_irq(&kernfs_notify_lock);

		/* kick poll */
		spin_lock_irq(&kernfs_open_node_lock);

		on = kn->attr.open;
		if (on) {
		atomic_inc(&on->event);
		wake_up_interruptible(&on->poll);
		}

		spin_unlock_irq(&kernfs_open_node_lock);

		/* kick fsnotify */
		mutex_lock(&kernfs_mutex);

		@@ -934,10 +922,21 @@ void kernfs_notify(struct kernfs_node *kn)
		{
		static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
		unsigned long flags;
		struct kernfs_open_node *on;

		if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
		return;

		/* kick poll immediately */
		spin_lock_irqsave(&kernfs_open_node_lock, flags);
		on = kn->attr.open;
		if (on) {
		atomic_inc(&on->event);
		wake_up_interruptible(&on->poll);
		}
		spin_unlock_irqrestore(&kernfs_open_node_lock, flags);

		/* schedule work to kick fsnotify */
		spin_lock_irqsave(&kernfs_notify_lock, flags);
		if (!kn->attr.notify_next) {
		kernfs_get(kn);

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