From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To: Johan Hovold <johan@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-samsung-soc@vger.kernel.org, linux-serial@vger.kernel.org,
linux-kernel@vger.kernel.org, marcan@marcan.st, arnd@kernel.org,
Andy Shevchenko <andy.shevchenko@gmail.com>
Subject: Re: [PATCH] tty: serial: samsung_tty: remove spinlock flags in interrupt handlers
Date: Tue, 16 Mar 2021 10:47:53 +0100 [thread overview]
Message-ID: <7f348e4c-3051-13cf-d461-eeda0ef53fdd@canonical.com> (raw)
In-Reply-To: <YFB0OcBg3Vj555eA@hovoldconsulting.com>
On 16/03/2021 10:02, Johan Hovold wrote:
> On Mon, Mar 15, 2021 at 07:12:12PM +0100, Krzysztof Kozlowski wrote:
>> Since interrupt handler is called with disabled local interrupts, there
>> is no need to use the spinlock primitives disabling interrupts as well.
>
> This isn't generally true due to "threadirqs" and that can lead to
> deadlocks if the console code is called from hard irq context.
>
> Now, this is *not* the case for this particular driver since it doesn't
> even bother to take the port lock in console_write(). That should
> probably be fixed instead.
>
> See https://lore.kernel.org/r/X7kviiRwuxvPxC8O@localhost.
Thanks for the link, quite interesting! For one type of device we have
two interrupts (RX and TX) so I guess it's a valid point/risk. However
let me try to understand it more.
Assuming we had only one interrupt line, how this interrupt handler with
threadirqs could be called from hardirq context?
You wrote there:
> For console drivers this can even happen for the same interrupt as the
> generic interrupt code can call printk(), and so can any other handler
> that isn't threaded (e.g. hrtimers or explicit IRQF_NO_THREAD).
However I replaced here only interrupt handler's spin lock to non-irq.
This code path will be executed only when interrupt is masked therefore
for one interrupt line there is *no possibility of*:
-> s3c64xx_serial_handle_irq
- interrupts are masked
- s3c24xx_serial_tx_irq
- spin_lock()
-> hrtimers or other IRQF_NO_THREAD
- console_write() or something
- s3c64xx_serial_handle_irq
- s3c24xx_serial_tx_irq
- spin_lock()
Best regards,
Krzysztof
next prev parent reply other threads:[~2021-03-16 9:48 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 18:12 [PATCH] tty: serial: samsung_tty: remove spinlock flags in interrupt handlers Krzysztof Kozlowski
2021-03-15 18:16 ` Andy Shevchenko
2021-03-16 9:02 ` Johan Hovold
2021-03-16 9:40 ` Andy Shevchenko
2021-03-19 6:36 ` Song Bao Hua (Barry Song)
2021-03-19 8:10 ` Johan Hovold
2021-03-19 10:09 ` Andy Shevchenko
2021-03-19 15:05 ` Johan Hovold
2021-03-16 9:47 ` Krzysztof Kozlowski [this message]
2021-03-16 9:56 ` Johan Hovold
2021-03-16 10:11 ` Krzysztof Kozlowski
2021-03-16 11:25 ` Johan Hovold
2021-03-22 11:23 ` Johan Hovold
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