From: robin.murphy@arm•com (Robin Murphy)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] serial/amba-pl011: Disable interrupts around TX softirq
Date: Fri, 05 Jun 2015 19:03:42 +0100 [thread overview]
Message-ID: <5571E47E.5020800@arm.com> (raw)
In-Reply-To: <1433513267-24163-1-git-send-email-Dave.Martin@arm.com>
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.
>
> 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)
>
next prev parent reply other threads:[~2015-06-05 18:03 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-05 14:07 [PATCH] serial/amba-pl011: Disable interrupts around TX softirq Dave Martin
2015-06-05 18:03 ` Robin Murphy [this message]
2015-06-08 10:34 ` Robin Murphy
2015-06-08 11:34 ` Dave P Martin
2015-06-13 0:39 ` Greg Kroah-Hartman
2015-06-15 10:53 ` Dave P Martin
2015-06-15 11:09 ` Andre Przywara
2015-06-15 14:03 ` Dave Martin
-- strict thread matches above, loose matches on Subject: below --
2015-06-18 13:54 Dave Martin
2015-06-20 9:09 ` Stefan Wahren
2015-06-23 11:13 ` Dave P Martin
2015-07-09 10:57 Dave Martin
2015-07-23 22:05 ` Greg Kroah-Hartman
2015-07-24 9:56 ` Dave Martin
2015-07-24 15:15 ` Greg Kroah-Hartman
2015-07-24 16:46 ` Dave Martin
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