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

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Date:   Wed, 11 Nov 2020 14:05:42 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Max Filippov <jcmvbkbc@...il.com>, linux-xtensa@...ux-xtensa.org
Cc:     Chris Zankel <chris@...kel.net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] xtensa: fix broken TIF_NOTIFY_SIGNAL assembly

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.

-- 
Jens Axboe