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Date:   Tue, 16 Aug 2022 13:48:48 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Will Deacon <will@kernel.org>, Tejun Heo <tj@kernel.org>,
        marcan@marcan.st, peterz@infradead.org, jirislaby@kernel.org,
        maz@kernel.org, mark.rutland@arm.com, boqun.feng@gmail.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
Subject: Re: [PATCH] workqueue: Fix memory ordering race in queue_work*()
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On Mon, Aug 15, 2022 at 10:27:10PM -0700, Linus Torvalds wrote:
>
> The bug seems to go back to commit e986a0d6cb36 ("locking/atomics,
> asm-generic/bitops/atomic.h: Rewrite using atomic_*() APIs"), and the
> fix looks to be as simple as just removing that early READ_ONCE return
> case (test_and_clear has the same bug).
> 
> Will?

I think this is the source of all this:

commit 61e02392d3c7ecac1f91c0a90a8043d67e081846
Author: Will Deacon <will@kernel.org>
Date:   Tue Feb 13 13:30:19 2018 +0000

    locking/atomic/bitops: Document and clarify ordering semantics for failed test_and_{}_bit()

Unfortunately it doesn't work because lots of kernel code rely on
the memory barrier semantics of test_and_set_bit.

If ARM really wants this change, then eitehr create a new API
for it or audit every single existing use in the kernel.

Patching the documentation and then relying on it is magical thinking.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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