From: Milton Miller Date: Thu, 8 Jan 2009 02:14:24 +0000 (+0000) Subject: hvc_console: Do not set low_latency when using interrupts X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=da9dc13289fa58dced12f2baff51dfb87c339ba3;p=openwrt%2Fstaging%2Fblogic.git hvc_console: Do not set low_latency when using interrupts hvc_console is setting low_latency unconditionally, but some clients are interrupt driven and will call hvc_poll from irq context. This will cause tty_flip_buffer_push to be called from irq context, and it very clearly states it must not be called from IRQ when low_latency is specified. Looking back through history: v2.6.16-rc1 via 33f0f88f1c51ae5c2d593d26960c760ea154c2e2 [PATCH] TTY layer buffering revamp added this new api. v2.6.16-rc3 via 8977d929e49021d9a6e031310aab01fa72f849c2 [PATCH] tty buffering stall fix claims to fix a stall discovered with hvc_console v2.6.16-rc5 via fb5c594c2acc441f0d2d8f457484a0e0e9285db3 [PATCH] Fix race condition in hvc console. said set this flag to avoid a stall problem, and was merged through the powerpc arch tree. Without searching for email discussions, it would appear to be an overlapping "fix", but one that did not consider all users. Signed-off-by: Benjamin Herrenschmidt --- diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index f2685b747fb9..0e18fdb9dddb 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -318,7 +318,8 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) } /* else count == 0 */ tty->driver_data = hp; - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ + if (!hp->irq_requested) + tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ hp->tty = tty;