2012-11-27 06:14:55

by Ilya Zykov

Subject: [PATCH v4] tty: Add driver unthrottle in ioctl(...,TCFLSH,..).

Sorry. More correct.

Regression 'tty: fix "IRQ45: nobody cared"'
Regression commit 7b292b4bf9a9d6098440d85616d6ca4c608b8304

Function reset_buffer_flags() also invoked during the ioctl(...,TCFLSH,..).
At the time of request we can have full buffers and throttled driver too.
If we don't unthrottle driver, we can get forever throttled driver, because,
after request, we will have empty buffers and throttled driver and
there is no place to unthrottle driver.
It simple reproduce with "pty" pair then one side sleep on tty->write_wait,
and other side do ioctl(...,TCFLSH,..). Then there is no place to do writers wake up.

Signed-off-by: Ilya Zykov <[email protected]>
---
diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index 12b1fa0..4071a8f 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -1096,12 +1096,16 @@ int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
ld = tty_ldisc_ref_wait(tty);
switch (arg) {
case TCIFLUSH:
- if (ld && ld->ops->flush_buffer)
+ if (ld && ld->ops->flush_buffer) {
ld->ops->flush_buffer(tty);
+ tty_unthrottle(tty);
+ }
break;
case TCIOFLUSH:
- if (ld && ld->ops->flush_buffer)
+ if (ld && ld->ops->flush_buffer) {
ld->ops->flush_buffer(tty);
+ tty_unthrottle(tty);
+ }
/* fall through */
case TCOFLUSH:
tty_driver_flush_buffer(tty);

2012-11-27 17:22:40

by Greg Kroah-Hartman

Subject: Re: [PATCH v4] tty: Add driver unthrottle in ioctl(...,TCFLSH,..).

On Tue, Nov 27, 2012 at 10:14:33AM +0400, Ilya Zykov wrote:
> Sorry. More correct.

In what way? Should I wait for the 6th version? :)

thanks,

greg k-h

2012-11-27 18:47:12

by Ilya Zykov

Subject: Re: [PATCH v4] tty: Add driver unthrottle in ioctl(...,TCFLSH,..).

On 27.11.2012 21:24, Greg Kroah-Hartman wrote:
> On Tue, Nov 27, 2012 at 10:14:33AM +0400, Ilya Zykov wrote:
>> Sorry. More correct.
>
> In what way? Should I wait for the 6th version? :)
>
> thanks,
>
> greg k-h
>

No, if only you will accept:
[PATCH]tty: Incorrect use tty_ldisc_flush() in TTY drivers.

It can be done another way, simple revert:
'tty: fix "IRQ45: nobody cared"'
commit 7b292b4bf9a9d6098440d85616d6ca4c608b8304

2012-11-27 19:27:04

by Alan

Subject: Re: [PATCH v4] tty: Add driver unthrottle in ioctl(...,TCFLSH,..).

> No, if only you will accept:
> [PATCH]tty: Incorrect use tty_ldisc_flush() in TTY drivers.
>
> It can be done another way, simple revert:
> 'tty: fix "IRQ45: nobody cared"'
> commit 7b292b4bf9a9d6098440d85616d6ca4c608b8304

NAK that revert - that swaps a minor glitch you've discovered that does
want fixing for a nasty bug.