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.

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)

-- 
1.7.10.4