linux-kernel - Re: [PATCH] rust: sync: add wait_interruptible

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Message-ID: <CAH5fLgj0gGxSWv1U+kjWTwAx7yfJCJ4u_cjfBwZjghZ5udbyuw@mail.gmail.com>
Date: Wed, 5 Feb 2025 13:15:31 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Miguel Ojeda <ojeda@...nel.org>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, 
	Waiman Long <longman@...hat.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: sync: add wait_interruptible_freezable

On Mon, Feb 3, 2025 at 3:30 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> On Mon, Feb 03, 2025 at 02:41:37PM +0100, Alice Ryhl wrote:
> > On Mon, Feb 3, 2025 at 2:38 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > On Mon, Feb 03, 2025 at 12:56:05PM +0100, Alice Ryhl wrote:
> > > > On Mon, Feb 3, 2025 at 12:54 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > > > >
> > > > > On Thu, Jan 30, 2025 at 11:30:44AM +0000, Alice Ryhl wrote:
> > > > > > Binder allows you to freeze a process where some of its threads are
> > > > > > blocked on the Binder driver. To make this work, we need to pass
> > > > > > TASK_FREEZABLE when going to sleep in the appropriate places. Thus, add
> > > > > > a new method wait_interruptible_freezable for the condition variable so
> > > > > > that sleeps where this is supported can be marked as such.
> > > > >
> > > > > The constraint on freezable is that you must not hold locks. There is a
> > > > > lockdep check for this in the code, but it would probably make sense to
> > > > > teach Rust about this constraint as well, hmm?
> > > >
> > > > Unfortunately, I don't think there's any way to enforce this at
> > > > compile time, but I'm definitely happy to add this in the
> > > > documentation.
> > >
> > > Ah, ISTR people talking about teaching Rust about the whole raw_spinlock
> > > vs spinlock vs mutex nesting order and figured if it can do that, then
>
> Peter, are you talking about the POC idea I proposed on tracking irqsave
> status:
>
>         https://lore.kernel.org/rust-for-linux/20241018055125.2784186-1-boqun.feng@gmail.com/
>
> ? I'm working on this right now, however, I don't think this would help
> spinlock or mutex nesting? Because there's no global(percpu) status of
> acquiring these locks. Am I missing something here?

I assumed that Peter was talking about klint, but I don't know.

Alice