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Re: [PATCH v11 2/9] xen: introduce generic non-atomic test_*bit()
- To: "Oleksii K." <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 28 May 2024 11:39:06 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 28 May 2024 09:39:27 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28.05.2024 10:37, Oleksii K. wrote:
> On Tue, 2024-05-28 at 08:20 +0200, Jan Beulich wrote:
>> On 24.05.2024 13:08, Oleksii Kurochko wrote:
>>> +/**
>>> + * generic_test_bit - Determine whether a bit is set
>>> + * @nr: bit number to test
>>> + * @addr: Address to start counting from
>>> + *
>>> + * This operation is non-atomic and can be reordered.
>>> + * If two examples of this operation race, one can appear to
>>> succeed
>>> + * but actually fail. You must protect multiple accesses with a
>>> lock.
>>> + */
>>
>> You got carried away updating comments - there's no raciness for
>> simple test_bit(). As is also expressed by its name not having those
>> double underscores that the others have.
> Then it is true for every function in this header. Based on the naming
> the conclusion can be done if it is atomic/npn-atomic and can/can't be
> reordered. So the comments aren't seem very useful.
I disagree - test_bit() is different, in not being a read-modify-write
operation.
Jan
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