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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 16 Aug 2022 09:58:56 -0700
Message-ID: <CAHk-=whn=gkf8kOxVPPeTpcgsFk21P9sk4SZRQ26=Jhqo6ewRA@mail.gmail.com>
Subject: Re: [PATCH] workqueue: Fix memory ordering race in queue_work*()
To:     Hector Martin <marcan@marcan.st>
Cc:     Boqun Feng <boqun.feng@gmail.com>, Will Deacon <will@kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Tejun Heo <tj@kernel.org>, peterz@infradead.org,
        jirislaby@kernel.org, maz@kernel.org, mark.rutland@arm.com,
        catalin.marinas@arm.com, oneukum@suse.com,
        roman.penyaev@profitbricks.com, asahi@lists.linux.dev,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
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On Tue, Aug 16, 2022 at 9:22 AM Hector Martin <marcan@marcan.st> wrote:
>
> It's worth pointing out that the workqueue code does *not* pair
> test_and_set_bit() with clear_bit(). It does an atomic_long_set()
> instead

Yes. That code is much too subtle.

And yes, I think those barriers are

 (a) misleading

 (b) don't work with the "serialize bits using spinlock" model at all

It's a good example of "we need to really have a better model for this".

             Linus