linux-kernel - Re: [patch V2 02/13] USB: serial: keyspan_pda: Replace in

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Message-ID: <20201027081647.GC4085@localhost>
Date:   Tue, 27 Oct 2020 09:16:47 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Johan Hovold <johan@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org,
        Thomas Winischhofer <thomas@...ischhofer.net>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-omap@...r.kernel.org, Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, Felipe Balbi <balbi@...nel.org>,
        Duncan Sands <duncan.sands@...e.fr>
Subject: Re: [patch V2 02/13] USB: serial: keyspan_pda: Replace
 in_interrupt() usage

On Mon, Oct 26, 2020 at 01:47:53PM +0100, Sebastian Andrzej Siewior wrote:
> On 2020-10-25 17:56:47 [+0100], Johan Hovold wrote:
> > There's a ton of issues with this driver, but this is arguably making
> > things worse. A line discipline may call write() from just about any
> > context so we cannot rely on tty being non-NULL here (e.g. PPP).
> 
> I wasn't aware of that. I've been looking at the callers each time a
> `tty' was passed it looked like a preemptible context (due to mutex /
> GFP_KERNEL) and so on.

Yeah, the default line discipline only calls in preemptible context
(these days), but others do not (e.g. see ppp_async_push()).

Johan