linux-kernel - Re: [PATCH v2] xtensa: fix broken TIF_NOTIFY

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Date:   Thu, 12 Nov 2020 01:12:36 -0800
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>, Chris Zankel <chris@...kel.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] xtensa: fix broken TIF_NOTIFY_SIGNAL assembly

On Wed, Nov 11, 2020 at 1:05 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> On 11/11/20 1:53 PM, Max Filippov wrote:
> > TIF_NOTIFY_SIGNAL handling in xtensa assembly is implemented
> > incorrectly: there should be a call to do_notify_resume when either
> > TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_NOTIFY_SIGNAL bit is set in the
> > thread_info::flags. The straightforward way to do it would be
> >
> >     _bbsi.l a4, TIF_NEED_RESCHED, 3f
> >     _bbsi.l a4, TIF_NOTIFY_RESUME, 2f
> >     _bbsi.l a4, TIF_NOTIFY_SIGNAL, 2f
> >     _bbci.l a4, TIF_SIGPENDING, 5f
> >
> > Optimize it a little bit and use bit mask and bnone opcode to skip
> > do_notify_resume invocation. Shuffle _TIF_* flags a bit so that used bit
> > mask fits into the immediate field of movi opcode.
>
> Thanks - do you mind if I fold this in with a reference to your
> changes? Seems like that'd be a better option than leaving it
> broken for a bit.

Sure Jens, by all means!

-- 
Thanks.
-- Max