linux-kernel - Re: [RFC PATCH 3/5] rust: block: allow `hrtimer::Timer` in `RequestData`

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Message-ID: <87sf043pfc.fsf@metaspace.dk>
Date: Tue, 02 Apr 2024 14:43:51 +0200
From: Andreas Hindborg <nmi@...aspace.dk>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Jens Axboe <axboe@...nel.dk>,  Christoph Hellwig <hch@....de>,  Keith
 Busch <kbusch@...nel.org>,  Damien Le Moal <Damien.LeMoal@....com>,  Bart
 Van Assche <bvanassche@....org>,  Hannes Reinecke <hare@...e.de>,
  "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,  Andreas
 Hindborg <a.hindborg@...sung.com>,  Niklas Cassel <Niklas.Cassel@....com>,
  Greg KH <gregkh@...uxfoundation.org>,  Matthew Wilcox
 <willy@...radead.org>,  Miguel Ojeda <ojeda@...nel.org>,  Alex Gaynor
 <alex.gaynor@...il.com>,  Wedson Almeida Filho <wedsonaf@...il.com>,
  Boqun Feng <boqun.feng@...il.com>,  Gary Guo <gary@...yguo.net>,
  Björn
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  Chaitanya Kulkarni <chaitanyak@...dia.com>,  Luis Chamberlain
 <mcgrof@...nel.org>,  Yexuan Yang <1182282462@...t.edu.cn>,  Sergio
 González Collado <sergio.collado@...il.com>,  Joel
 Granados
 <j.granados@...sung.com>,  "Pankaj Raghav (Samsung)"
 <kernel@...kajraghav.com>,  Daniel Gomez <da.gomez@...sung.com>,  open
 list <linux-kernel@...r.kernel.org>,  "rust-for-linux@...r.kernel.org"
 <rust-for-linux@...r.kernel.org>,  "lsf-pc@...ts.linux-foundation.org"
 <lsf-pc@...ts.linux-foundation.org>,  "gost.dev@...sung.com"
 <gost.dev@...sung.com>
Subject: Re: [RFC PATCH 3/5] rust: block: allow `hrtimer::Timer` in
 `RequestData`

Benno Lossin <benno.lossin@...ton.me> writes:

> On 3/13/24 12:05, Andreas Hindborg wrote:> From: Andreas Hindborg <a.hindborg@...sung.com>
>> 
>> Signed-off-by: Andreas Hindborg <a.hindborg@...sung.com>
>> ---
>>   rust/kernel/block/mq/request.rs | 67 ++++++++++++++++++++++++++++++++-
>>   1 file changed, 66 insertions(+), 1 deletion(-)
>> 
>> diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request.rs
>> index cccffde45981..8b7f08f894be 100644
>> --- a/rust/kernel/block/mq/request.rs
>> +++ b/rust/kernel/block/mq/request.rs
>> @@ -4,13 +4,16 @@
>>   //!
>>   //! C header: [`include/linux/blk-mq.h`](srctree/include/linux/blk-mq.h)
>> 
>> +use kernel::hrtimer::RawTimer;
>> +
>>   use crate::{
>>       bindings,
>>       block::mq::Operations,
>>       error::{Error, Result},
>> +    hrtimer::{HasTimer, TimerCallback},
>>       types::{ARef, AlwaysRefCounted, Opaque},
>>   };
>> -use core::{ffi::c_void, marker::PhantomData, ops::Deref};
>> +use core::{ffi::c_void, marker::PhantomData, ops::Deref, ptr::NonNull};
>> 
>>   use crate::block::bio::Bio;
>>   use crate::block::bio::BioIterator;
>> @@ -175,6 +178,68 @@ fn deref(&self) -> &Self::Target {
>>       }
>>   }
>> 
>> +impl<T> RawTimer for RequestDataRef<T>
>> +where
>> +    T: Operations,
>> +    T::RequestData: HasTimer<T::RequestData>,
>> +    T::RequestData: Sync,
>> +{
>> +    fn schedule(self, expires: u64) {
>> +        let self_ptr = self.deref() as *const T::RequestData;
>> +        core::mem::forget(self);
>> +
>> +        // SAFETY: `self_ptr` is a valid pointer to a `T::RequestData`
>> +        let timer_ptr = unsafe { T::RequestData::raw_get_timer(self_ptr) };
>> +
>> +        // `Timer` is `repr(transparent)`
>> +        let c_timer_ptr = timer_ptr.cast::<bindings::hrtimer>();
>> +
>> +        // Schedule the timer - if it is already scheduled it is removed and
>> +        // inserted
>> +
>> +        // SAFETY: c_timer_ptr points to a valid hrtimer instance that was
>> +        // initialized by `hrtimer_init`
>> +        unsafe {
>> +            bindings::hrtimer_start_range_ns(
>> +                c_timer_ptr as *mut _,
>> +                expires as i64,
>> +                0,
>> +                bindings::hrtimer_mode_HRTIMER_MODE_REL,
>> +            );
>> +        }
>> +    }
>> +}
>> +
>> +impl<T> kernel::hrtimer::RawTimerCallback for RequestDataRef<T>
>> +where
>> +    T: Operations,
>> +    T: Sync,
>
> Why is this needed? Shouldn't this be `T::RequestData: Sync`?
>
> Is the `run` function below executed on a different thread compared to
> the `schedule` function above?
> If yes, then `T::RequestData` probably also needs to be `Send`.
> You also would need to adjust the bounds in the impl above.

It's a typo, thanks for spotting. It should be `T::RequestData: Sync`.

BR Andreas