linux-kernel - Re: UART/TTY console deadlock

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Message-ID: <20200708080712.GC571@jagdpanzerIV.localdomain>
Date:   Wed, 8 Jul 2020 17:07:12 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Petr Mladek <pmladek@...e.com>,
        Raul Rangel <rrangel@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "S, Shirish" <Shirish.S@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        John Ogness <john.ogness@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: UART/TTY console deadlock

On (20/07/08 09:40), Kurt Kanzenbach wrote:
> I'm not sure how this patch will help with the situation. Because at the
> point of that THRE test the irq handler isn't registered. It's
> registered a few lines below (up->ops->setup_irq()) meaning the irq line
> has to be disabled if shared. Otherwise the kernel might detect a
> spurious irq and disables it. That's at least my understanding of the
> problem (see commit message from 54e53b2e8081 ("tty: serial: 8250: pass
> IRQ shared flag to UART ports")).

So the only remaining approach then is to move
disable_irq_nosync()/enable_irq() out of port->lock
scope.

	-ss