linux-kernel - Re: [PATCH] kthread: Fix race condition between kthread_parkme() and kthread

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Message-ID: <alpine.DEB.2.20.1709290958450.1890@nanos>
Date:   Fri, 29 Sep 2017 09:59:55 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Junaid Shahid <junaids@...gle.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        Andres Lagar-Cavilla <andreslc@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] kthread: Fix race condition between kthread_parkme()
 and kthread_unpark()

On Thu, 28 Sep 2017, Junaid Shahid wrote:

> Hi Peter,
> 
> It looks like try_cmpxchg is not available on non-x86 archs, but other than
> that the version that you proposed looks good.
> 
> One thing that I am a bit curious about is that the original code, before
> either patch, had a test_and_set_bit for KTHREAD_IS_PARKED rather than just
> a set_bit. I can't think of any reason why that was needed, since it
> doesn't look like TASK_PARKED tasks are susceptible to spurious wakeups. Do
> you by any chance happen to know if there was any specific reason for it?

Everything is susceptible to spurious wakeups and has to deal with it.

Thanks,

	tglx