linux-kernel - [PATCH] usb: xhci: Replace tasklet with work

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Date:   Mon, 18 Jan 2021 16:09:30 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     gregkh@...uxfoundation.org
Cc:     mathias.nyman@...el.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, dave@...olabs.net,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH] usb: xhci: Replace tasklet with work

Tasklets have long been deprecated as being too heavy on the system
by running in irq context - and this is not a performance critical
path. If a higher priority process wants to run, it must wait for
the tasklet to finish before doing so.

dbc_rx_push() will now run in process context and have further
concurrency - tasklets being serialized among themselves, but this
is done holding the port_lock, so it should be fine.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 drivers/usb/host/xhci-dbgcap.h |  2 +-
 drivers/usb/host/xhci-dbgtty.c | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h
index c70b78d504eb..aec66009af51 100644
--- a/drivers/usb/host/xhci-dbgcap.h
+++ b/drivers/usb/host/xhci-dbgcap.h
@@ -104,7 +104,7 @@ struct dbc_port {
 	struct list_head		read_pool;
 	struct list_head		read_queue;
 	unsigned int			n_read;
-	struct tasklet_struct		push;
+	struct work_struct		push;
 
 	struct list_head		write_pool;
 	struct kfifo			write_fifo;
diff --git a/drivers/usb/host/xhci-dbgtty.c b/drivers/usb/host/xhci-dbgtty.c
index ae4e4ab638b5..50da77d92cf6 100644
--- a/drivers/usb/host/xhci-dbgtty.c
+++ b/drivers/usb/host/xhci-dbgtty.c
@@ -108,7 +108,7 @@ dbc_read_complete(struct xhci_dbc *dbc, struct dbc_request *req)
 
 	spin_lock_irqsave(&port->port_lock, flags);
 	list_add_tail(&req->list_pool, &port->read_queue);
-	tasklet_schedule(&port->push);
+	schedule_work(&port->push);
 	spin_unlock_irqrestore(&port->port_lock, flags);
 }
 
@@ -272,7 +272,7 @@ static void dbc_tty_unthrottle(struct tty_struct *tty)
 	unsigned long		flags;
 
 	spin_lock_irqsave(&port->port_lock, flags);
-	tasklet_schedule(&port->push);
+	schedule_work(&port->push);
 	spin_unlock_irqrestore(&port->port_lock, flags);
 }
 
@@ -288,15 +288,18 @@ static const struct tty_operations dbc_tty_ops = {
 	.unthrottle		= dbc_tty_unthrottle,
 };
 
-static void dbc_rx_push(struct tasklet_struct *t)
+static void dbc_rx_push(struct work_struct *work)
 {
 	struct dbc_request	*req;
 	struct tty_struct	*tty;
 	unsigned long		flags;
 	bool			do_push = false;
 	bool			disconnect = false;
-	struct dbc_port		*port = from_tasklet(port, t, push);
-	struct list_head	*queue = &port->read_queue;
+	struct dbc_port		*port;
+	struct list_head	*queue;
+
+	port = container_of(work, struct dbc_port, push);
+	queue = &port->read_queue;
 
 	spin_lock_irqsave(&port->port_lock, flags);
 	tty = port->port.tty;
@@ -349,7 +352,7 @@ static void dbc_rx_push(struct tasklet_struct *t)
 	if (!list_empty(queue) && tty) {
 		if (!tty_throttled(tty)) {
 			if (do_push)
-				tasklet_schedule(&port->push);
+				schedule_work(&port->push);
 			else
 				pr_warn("ttyDBC0: RX not scheduled?\n");
 		}
@@ -382,7 +385,7 @@ xhci_dbc_tty_init_port(struct xhci_dbc *dbc, struct dbc_port *port)
 {
 	tty_port_init(&port->port);
 	spin_lock_init(&port->port_lock);
-	tasklet_setup(&port->push, dbc_rx_push);
+	INIT_WORK(&port->push, dbc_rx_push);
 	INIT_LIST_HEAD(&port->read_pool);
 	INIT_LIST_HEAD(&port->read_queue);
 	INIT_LIST_HEAD(&port->write_pool);
@@ -394,7 +397,7 @@ xhci_dbc_tty_init_port(struct xhci_dbc *dbc, struct dbc_port *port)
 static void
 xhci_dbc_tty_exit_port(struct dbc_port *port)
 {
-	tasklet_kill(&port->push);
+	cancel_work_sync(&port->push);
 	tty_port_destroy(&port->port);
 }
 
-- 
2.26.2