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@xxxxxxx>
---
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.
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)
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
