Re: [PATCH] tty: serial: samsung_tty: remove spinlock flags in interrupt handlers

From: Johan Hovold <johan@kernel.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
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 10:02:49 +0100	[thread overview]
Message-ID: <YFB0OcBg3Vj555eA@hovoldconsulting.com> (raw)
In-Reply-To: <20210315181212.113217-1-krzysztof.kozlowski@canonical.com>

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.

Johan