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kernfs: Improve kernfs_notify() poll notification latency

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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>
This commit is contained in:
Radu Rendec 2018-11-15 21:09:54 -05:00 committed by Greg Kroah-Hartman
parent 6be244dcd5
commit 03c0a9208b
1 changed files with 11 additions and 12 deletions
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23
fs/kernfs/file.c
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@ -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);