From: Johan Hovold <johan@kernel.org>
To: "tiantao (H)" <tiantao6@huawei.com>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Johan Hovold <johan@kernel.org>,
Tian Tao <tiantao6@hisilicon.com>,
gregkh@linuxfoundation.org, jirislaby@kernel.org,
afaerber@suse.de, manivannan.sadhasivam@linaro.org,
linux-serial@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tty: serial: replace spin_lock_irqsave by spin_lock in hard IRQ
Date: Fri, 20 Nov 2020 13:49:57 +0100 [thread overview]
Message-ID: <X7e7dYlYxPDsj71G@localhost> (raw)
In-Reply-To: <9ce93d7b-f769-58ed-e6bf-95c34bd0123e@huawei.com>
On Fri, Nov 20, 2020 at 07:25:03PM +0800, tiantao (H) wrote:
> 在 2020/11/20 16:23, Johan Hovold 写道:
> > On Thu, Nov 19, 2020 at 05:01:29PM +0800, Tian Tao wrote:
> >> The code has been in a irq-disabled context since it is hard IRQ. There
> >> is no necessity to do it again.
> >>
> >> Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
> >> ---
> >> drivers/tty/serial/owl-uart.c | 5 ++---
> >> 1 file changed, 2 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
> >> index c149f8c3..472fdaf 100644
> >> --- a/drivers/tty/serial/owl-uart.c
> >> +++ b/drivers/tty/serial/owl-uart.c
> >> @@ -251,10 +251,9 @@ static void owl_uart_receive_chars(struct uart_port *port)
> >> static irqreturn_t owl_uart_irq(int irq, void *dev_id)
> >> {
> >> struct uart_port *port = dev_id;
> >> - unsigned long flags;
> >> u32 stat;
> >>
> >> - spin_lock_irqsave(&port->lock, flags);
> >> + spin_lock(&port->lock);
> >
> > Same thing here; this will break with forced irq threading (i.e.
> > "threadirqs") since the console code can still end up being called from
> > interrupt context.
> As the following code shows, owl_uart_irq does not run in the irq
> threading context.
> ret = request_irq(port->irq, owl_uart_irq, IRQF_TRIGGER_HIGH,
> "owl-uart", port);
> if (ret)
> return ret;
It still runs in a thread when interrupts are forced to be threaded
using the kernel parameter "threadirqs".
We just had a revert of a change like yours after lockdep reported the
resulting lock inversion with forced interrupt threading.
Whether drivers should have to care about "threadirqs" is a somewhat
different question. Not sure how that's even supposed to work generally
unless we mass-convert drivers to spin_lock_irqsave() (or mark their
interrupts IRQF_NO_THREAD).
Thomas, any comments?
Johan
next prev parent reply other threads:[~2020-11-20 12:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 9:01 [PATCH] tty: serial: replace spin_lock_irqsave by spin_lock in hard IRQ Tian Tao
2020-11-19 9:03 ` Jiri Slaby
2020-11-20 8:23 ` Johan Hovold
2020-11-20 11:25 ` tiantao (H)
2020-11-20 12:49 ` Johan Hovold [this message]
2020-11-20 20:00 ` David Laight
2020-11-21 15:17 ` Johan Hovold
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