linux-kernel - Re: [PATCH v8 4/7] rust: time: Add wrapper for fsleep function

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Message-Id: <20250117.185501.1171065234025373111.fujita.tomonori@gmail.com>
Date: Fri, 17 Jan 2025 18:55:01 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: aliceryhl@...gle.com
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Subject: Re: [PATCH v8 4/7] rust: time: Add wrapper for fsleep function

On Fri, 17 Jan 2025 10:13:08 +0100
Alice Ryhl <aliceryhl@...gle.com> wrote:

> On Fri, Jan 17, 2025 at 10:01 AM FUJITA Tomonori
> <fujita.tomonori@...il.com> wrote:
>>
>> On Fri, 17 Jan 2025 16:53:26 +0900 (JST)
>> FUJITA Tomonori <fujita.tomonori@...il.com> wrote:
>>
>> > On Thu, 16 Jan 2025 10:27:02 +0100
>> > Alice Ryhl <aliceryhl@...gle.com> wrote:
>> >
>> >>> +/// This function can only be used in a nonatomic context.
>> >>> +pub fn fsleep(delta: Delta) {
>> >>> +    // The argument of fsleep is an unsigned long, 32-bit on 32-bit architectures.
>> >>> +    // Considering that fsleep rounds up the duration to the nearest millisecond,
>> >>> +    // set the maximum value to u32::MAX / 2 microseconds.
>> >>> +    const MAX_DURATION: Delta = Delta::from_micros(u32::MAX as i64 >> 1);
>> >>
>> >> Hmm, is this value correct on 64-bit platforms?
>> >
>> > You meant that the maximum can be longer on 64-bit platforms? 2147484
>> > milliseconds is long enough for fsleep's duration?
>> >
>> > If you prefer, I use different maximum durations for 64-bit and 32-bit
>> > platforms, respectively.
>>
>> How about the following?
>>
>> const MAX_DURATION: Delta = Delta::from_micros(usize::MAX as i64 >> 1);
> 
> Why is there a maximum in the first place? Are you worried about
> overflow on the C side?

Yeah, Boqun is concerned that an incorrect input (a negative value or
an overflow on the C side) leads to unintentional infinite sleep:

https://lore.kernel.org/lkml/ZxwVuceNORRAI7FV@Boquns-Mac-mini.local/