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

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Message-ID: <7998b455-c7bd-5caf-d6a9-d1c0404f2b5f@kernel.dk>
Date:   Thu, 12 Nov 2020 08:45:01 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Max Filippov <jcmvbkbc@...il.com>
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 11/12/20 2:12 AM, Max Filippov wrote:
> 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! Done.

-- 
Jens Axboe