On Tue, 2006-12-26 at 01:08 +0059, Jiri Slaby wrote: > Hi! > > * tty_flip_buffer_push - terminal > * @tty: tty to push > * > * 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... > Moreover, hvsi says: > tty->low_latency = 1; /* avoid throttle/tty_flip_buffer_push race */ That was a long time ago, but the race is something like this: * data is received, enough to completely fill the tty buffer * tty_flip_buffer_push() schedules flush_to_ldisc() * before flush_to_ldisc() runs, more data is received * flush_to_ldisc() truncates the incoming data (look for tty->receive_room) I don't see how this is supposed to work in general. I suppose most PC-standard char drivers are not capable of overflowing a tty buffer before the host can empty it. I wasn't comfortable with hoping for that condition in my driver. Setting "low_latency" ensures that throttle will be called immediately if the tty buffer is filled, avoiding the race. -- Hollis Blanchard IBM Linux Technology Center - 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/