linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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

  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 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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=X7e7dYlYxPDsj71G@localhost \
    --to=johan@kernel.org \
    --cc=afaerber@suse.de \
    --cc=gregkh@linuxfoundation.org \
    --cc=jirislaby@kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-serial@vger.kernel.org \
    --cc=manivannan.sadhasivam@linaro.org \
    --cc=tglx@linutronix.de \
    --cc=tiantao6@hisilicon.com \
    --cc=tiantao6@huawei.com \
    --subject='Re: [PATCH] tty: serial: replace spin_lock_irqsave by spin_lock in hard IRQ' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).