Messages in this thread | | | Date | Thu, 26 May 2011 00:11:04 -0700 | From | Greg KH <> | Subject | Re: tty_lock held during transmit wait in close: still unresolved |
| |
On Thu, May 26, 2011 at 01:59:22AM +0200, Andreas Bombe wrote: > Short reminder/summary: Unlike the BKL, the tty_lock mechanism that > replaced it does not release the lock while sleeping. This causes the > tty_lock to be held for extended periods of time when uart_close() > (running with tty_lock held) tries to flush the transmit buffer but is > unable to do so. > > The result is that until the transmit flush completes by the remote end > finally accepting the data or the driver timing out and giving up, > pretty much all tty operations freeze. No programs can be started > and for some reason X freezes for me. From a user viewpoint, the > computer effectively locks up for that time. > > After I tracked the issue down to the tty_lock mechanism, I found some > discussion on LKML about that from last November (thread starting here: > http://lkml.kernel.org/r/4CCBCD8E.1020601@billauer.co.il ). However > nothing has come of it, it appears, at least not in the official kernel. > > A minimalist way to trigger this issue is with a serial port that has > nothing attached: > > stty -F /dev/ttyS0 crtscts > echo >/dev/ttyS0 > > The echo triggers a 30 second timeout on close while the driver is > trying to flush the newline. Another way is developing an USB device > with a virtual serial port and having it stop (by debugger or > crash/lockup)... > > Any ideas on how to progress?
Can you try Linus's tree right now? A number of changes went in during this merge window that might help out here I think.
thanks,
greg k-h
| |