On Tue, 2007-01-02 at 11:17 -0600, Hollis Blanchard wrote:
> On Tue, 2006-12-26 at 01:08 +0059, Jiri Slaby wrote:
> > * Queue a push of the terminal flip buffers to the line discipline. This
> > * function must not be called from IRQ context if tty->low_latency is set.
> >
> > But some drivers (mxser, nozomi, hvsi...) sets low_latency to 1 in _open and
> > calls tty_flip_buffer_push in isr or in functions, which are called from isr.
> > Is the comment correct or the drivers?
>
> The comment would be true if tty_flip_buffer_push() attempted to block
> with tty->low_latency set, but it doesn't AFAICS. One possibility for
> deadlock is if the tty->buf.lock spinlock is taken on behalf of a user
> process...
There is no deadlock on tty->buf.lock,
which is always acquired with spin_lock_irqsave()
and is only used by the tty buffering code.
The only deadlock I know of with the current tty buffering code
is calling tty_flip_buffer_push() with low_latency
set and from the ISR of a driver that has a problem
with the line discipline calling back into the driver.
The standard serial core has (or at least had the last time
I looked) this problem with the N_TTY ldisc:
driver gets internal spinlock in ISR
driver calls tty_flip_buffer_push with low_latency = 1
flush_to_ldisc() immediately passes data to line discipline
line discipline calls back into driver
driver tries again to get internal spinlock
With low_latency == 1, flush_to_ldisc() is deferred
until the ISR is complete and the internal spinlock is released.
I forget the exact driver callback that caused this.
--
Paul Fulghum
Microgate Systems, Ltd
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
