From: Hector Martin <marcan@marcan.st>
To: Herbert Xu <herbert@gondor.apana.org.au>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: tj@kernel.org, will@kernel.org, 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*()
Date: Tue, 16 Aug 2022 14:37:33 +0900 [thread overview]
Message-ID: <923f9638-d443-cb8e-104f-41a7f34fa25c@marcan.st> (raw)
In-Reply-To: <YvsZvwxACuGw3KIt@gondor.apana.org.au>
On 16/08/2022 13.14, Herbert Xu wrote:
> Hector Martin <marcan@marcan.st> wrote:
>>
>> This has been broken since the dawn of time, and it was incompletely
>> fixed by 346c09f80459, which added the necessary barriers in the work
>> execution path but failed to account for the missing barrier in the
>> test_and_set_bit() failure case. Fix it by switching to
>> atomic_long_fetch_or(), which does have unconditional barrier semantics
>> regardless of whether the bit was already set or not (this is actually
>> just test_and_set_bit() minus the early exit path).
>
> test_and_set_bit is supposed to contain a full memory barrier.
> If it doesn't then your arch is broken and needs to be fixed.
>
> Changing this one spot is pointless because such assumptions
> are all over the kernel.
Documentation/atomic_bitops.txt and the asm-generic implementaton
disagree with you, so this isn't quite as simple as "your arch is
broken" :-)
- Hector
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prev parent reply other threads:[~2022-08-16 5:38 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-15 17:58 [PATCH] workqueue: Fix memory ordering race in queue_work*() Hector Martin
2022-08-15 19:10 ` Tejun Heo
2022-08-16 4:15 ` Herbert Xu
2022-08-16 5:27 ` Linus Torvalds
2022-08-16 5:36 ` Hector Martin
2022-08-16 5:52 ` Linus Torvalds
2022-08-16 6:28 ` Hector Martin
2022-08-16 7:48 ` Herbert Xu
2022-08-16 8:01 ` Hector Martin
2022-08-16 5:48 ` Herbert Xu
2022-08-16 6:03 ` Linus Torvalds
2022-08-16 13:41 ` Will Deacon
2022-08-16 14:55 ` Boqun Feng
2022-08-16 16:22 ` Hector Martin
2022-08-16 16:43 ` Boqun Feng
2022-08-16 16:58 ` Linus Torvalds
2022-08-16 16:41 ` Linus Torvalds
2022-08-17 5:05 ` Herbert Xu
2022-08-16 17:01 ` Tejun Heo
2022-08-16 16:26 ` Tejun Heo
2022-08-16 17:21 ` Hector Martin
2022-08-16 4:14 ` Herbert Xu
2022-08-16 5:37 ` Hector Martin [this message]
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