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SubjectRe: Locking problem in usbserial with 2.6.23-git 5a34417f
On Fri, 19 Oct 2007, Larry Finger wrote:

> As I said earlier, the lock problem went away; however, I get the
> following two kernel warnings:

That's because I messed up the patch, sorry. The one below should work

From: Jiri Kosina <>

USB: usbserial - fix potential deadlock between write() and IRQ

usb_serial_generic_write() doesn't disable interrupts when taking port->lock,
and could therefore deadlock with usb_serial_generic_read_bulk_callback()
being called from interrupt, taking the same lock. Fix it.

Signed-off-by: Jiri Kosina <>

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 88a2c7d..9eb4a65 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -208,14 +208,15 @@ int usb_serial_generic_write(struct usb_serial_port *port, const unsigned char *

/* only do something if we have a bulk out endpoint */
if (serial->num_bulk_out) {
- spin_lock_bh(&port->lock);
+ unsigned long flags;
+ spin_lock_irqsave(&port->lock, flags);
if (port->write_urb_busy) {
- spin_unlock_bh(&port->lock);
+ spin_unlock_irqrestore(&port->lock, flags);
dbg("%s - already writing", __FUNCTION__);
return 0;
port->write_urb_busy = 1;
- spin_unlock_bh(&port->lock);
+ spin_unlock_irqrestore(&port->lock, flags);

count = (count > port->bulk_out_size) ? port->bulk_out_size : count;

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