[PATCH] serial/amba-pl011: Disable interrupts around TX softirq
From: robin.murphy@arm.com (Robin Murphy)
Date: 2015-06-05 18:03:42
Also in:
linux-serial
On 05/06/15 15:07, Dave P Martin wrote:
pl011_tx_softirq() currently uses spin_{,un}lock(), which are not
sufficient to inhibit pl011_int() from being triggered by a local
IRQ and trying to re-take the same lock. This can lead to
deadlocks.
This patch uses the _irq() locking variants instead to ensure that
pl011_int() handling for a given port is deferred until any
pl011_tx_softirq() work for that port is complete.
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
Another candidate for v4.1 if possible (sorry!) -- I thought this change
was already in, but it went astray when I was refactoring.
This patch conflicts with tty-next like the previous patch, since it
fixes code that is removed by tty-next. The correct resolution for
the resulting merge conflict is to keep the code from tty-next.
I am not 100% certain yet whether some rare deadlocks that Robin is
seeing are caused by this issue, or whether this patch fixes them --
he's testing atm.FWIW, I've been running Juno in a startup/shutdown loop with a very noisy systemd all afternoon and haven't hit a problem yet with this patch applied. Testing without this patch yesterday I saw 3 or 4 lockdep splats in about the same amount of time. I'll leave it going over the weekend just to make sure, though. Robin.
quoted hunk ↗ jump to hunk
The patch is straightforward and using non _irq() locking in a workitem that expects the lock to protect against interrupt handlers on the same CPU is clearly wrong. Cheers ---Dave drivers/tty/serial/amba-pl011.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 763eb20..0cc622a 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c@@ -1360,9 +1360,9 @@ static void pl011_tx_softirq(struct work_struct *work) struct uart_amba_port *uap = container_of(dwork, struct uart_amba_port, tx_softirq_work); - spin_lock(&uap->port.lock); + spin_lock_irq(&uap->port.lock); while (pl011_tx_chars(uap)) ; - spin_unlock(&uap->port.lock); + spin_unlock_irq(&uap->port.lock); } static void pl011_tx_irq_seen(struct uart_amba_port *uap)