From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from forward502d.mail.yandex.net (forward502d.mail.yandex.net [178.154.239.210]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AF02118EAB; Sun, 7 Sep 2025 08:43:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.154.239.210 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757234624; cv=none; b=UKcNP2tOjKnhLvuEb96us3U1Y8sBDH+FIjoDznmYCm4UpxXMs8iTmmr8goLbQpyEkVeAEfDek0a/6adsMGc5oNJPQKul+n84plfZD8uP8zqy/fvveNHu/i0xkJjFf57jJfCp/ufoq7hA16jN12Cqi7rwVw79FOuLdRiLb1oiKhk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757234624; c=relaxed/simple; bh=rDgGdEgB5A7k9qddy1JKxSM/owkiMEXnT3pIHNXpXO8=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=d3VetIg16XWYMpXUH3ePlTbuU+lHuZq1PVnPwqNubDm9lR+NHi01hW97kN4Ope/AthHEhNmatwKxmuiQMRCAYFZJnmRRzVlYU2+OD7fEu0JEX+pH9TaF+EVla7HIEr5t9fGkUL2cWs0+xqDA2C741Vj9gg+ATevv0rF9JUtVj5k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=onurozkan.dev; spf=pass smtp.mailfrom=onurozkan.dev; dkim=pass (1024-bit key) header.d=onurozkan.dev header.i=@onurozkan.dev header.b=Z0B8A6Nt; arc=none smtp.client-ip=178.154.239.210 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=onurozkan.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=onurozkan.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=onurozkan.dev header.i=@onurozkan.dev header.b="Z0B8A6Nt" Received: from mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net (mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net [IPv6:2a02:6b8:c0c:4720:0:640:9548:0]) by forward502d.mail.yandex.net (Yandex) with ESMTPS id 9EFA5C0A8F; Sun, 07 Sep 2025 11:38:23 +0300 (MSK) Received: by mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net (smtp/Yandex) with ESMTPSA id HcfaraXMqqM0-M3gFR5Jm; Sun, 07 Sep 2025 11:38:22 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=onurozkan.dev; s=mail; t=1757234302; bh=sr1v7CnmN+LAWW7mBJAZyqFsgNPJVxqWyr//sA/8lI8=; h=Cc:Message-ID:Subject:Date:References:To:From:In-Reply-To; b=Z0B8A6NtXX6W0nPzOYO8mM66ueVGMVI+KH7EMbJKLtBE715ivmgh2ASlw+VWFEAE6 ofH/Q/CR/I8oytEFLFC7vvZi/vQ/A7iiq+vqplzthvGII+o0Wy7M+aJjRoIRoQD7iA 5jZOYl0yk9ra3mIM9opFjJW7X6IeVTPI33HTQB1A= Authentication-Results: mail-nwsmtp-smtp-production-main-59.iva.yp-c.yandex.net; dkim=pass header.i=@onurozkan.dev Date: Sun, 7 Sep 2025 11:38:17 +0300 From: Onur To: Daniel Almeida Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, lossin@kernel.org, lyude@redhat.com, ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, dakr@kernel.org, peterz@infradead.org, mingo@redhat.com, will@kernel.org, longman@redhat.com, felipe_life@live.com, daniel@sedlak.dev, bjorn3_gh@protonmail.com Subject: Re: [PATCH v6 6/7] rust: ww_mutex/exec: add high-level API Message-ID: <20250907113817.768acf3d@nimda.home> In-Reply-To: <20250907112006.6bdbb478@nimda.home> References: <20250903131313.4365-1-work@onurozkan.dev> <20250903131313.4365-7-work@onurozkan.dev> <6D30FEF7-07E7-4851-A7A2-76649AD0B217@collabora.com> <20250906141310.2c29aa8e@nimda.home> <2B16DBF4-1F6C-4025-8373-5651867B7D49@collabora.com> <20250907112006.6bdbb478@nimda.home> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.50; x86_64-unknown-linux-gnu) Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Sun, 7 Sep 2025 11:20:06 +0300 Onur wrote: > On Sat, 6 Sep 2025 12:04:34 -0300 > Daniel Almeida wrote: >=20 > >=20 > >=20 > > > On 6 Sep 2025, at 08:13, Onur wrote: > > >=20 > > > On Fri, 5 Sep 2025 16:42:09 -0300 > > > Daniel Almeida wrote: > > >=20 > > >> Hi Onur, > > >>=20 > > >>> On 3 Sep 2025, at 10:13, Onur =C3=96zkan wrote: > > >>>=20 > > >>> `ExecContext` is a helper built on top of ww_mutex > > >>=20 > > >> Again, I wonder what people think about this particular name. > > >>=20 > > >>> that provides a retrying interface for lock acquisition. > > >>> When `EDEADLK` is hit, it drops all held locks, resets > > >>> the acquire context and retries the given (by the user) > > >>> locking algorithm until it succeeds. > > >>>=20 > > >>> The API keeps track of acquired locks, cleans them up > > >>> automatically and allows data access to the protected > > >>> data through `with_locked()`. The `lock_all()` helper > > >>> allows implementing multi-mutex algorithms in a simpler > > >>> and less error-prone way while keeping the ww_mutex > > >>> semantics. > > >>>=20 > > >>=20 > > >> Great, this was exactly what I was looking for! :) > > >>=20 > > >>> Signed-off-by: Onur =C3=96zkan > > >>> --- > > >>> rust/kernel/sync/lock/ww_mutex.rs | 2 + > > >>> rust/kernel/sync/lock/ww_mutex/exec.rs | 176 > > >>> +++++++++++++++++++++++++ 2 files changed, 178 insertions(+) > > >>> create mode 100644 rust/kernel/sync/lock/ww_mutex/exec.rs > > >>>=20 > > >>> diff --git a/rust/kernel/sync/lock/ww_mutex.rs > > >>> b/rust/kernel/sync/lock/ww_mutex.rs index > > >>> b415d6deae9b..7de6578513e5 100644 --- > > >>> a/rust/kernel/sync/lock/ww_mutex.rs +++ > > >>> b/rust/kernel/sync/lock/ww_mutex.rs @@ -16,6 +16,8 @@ > > >>> use core::cell::UnsafeCell; > > >>> use core::marker::PhantomData; > > >>>=20 > > >>> +pub mod exec; > > >>> + > > >>> /// Create static [`WwClass`] instances. > > >>> /// > > >>> /// # Examples > > >>> diff --git a/rust/kernel/sync/lock/ww_mutex/exec.rs > > >>> b/rust/kernel/sync/lock/ww_mutex/exec.rs new file mode 100644 > > >>> index 000000000000..2f1fc540f0b8 > > >>> --- /dev/null > > >>> +++ b/rust/kernel/sync/lock/ww_mutex/exec.rs > > >>> @@ -0,0 +1,176 @@ > > >>> +// SPDX-License-Identifier: GPL-2.0 > > >>> + > > >>> +//! A high-level [`WwMutex`] execution helper. > > >>> +//! > > >>> +//! Provides a retrying lock mechanism on top of [`WwMutex`] > > >>> and [`WwAcquireCtx`]. +//! It detects [`EDEADLK`] and handles > > >>> it by rolling back and retrying the +//! user-supplied locking > > >>> algorithm until success. + > > >>> +use crate::prelude::*; > > >>> +use crate::sync::lock::ww_mutex::{WwAcquireCtx, WwClass, > > >>> WwMutex, WwMutexGuard}; +use core::ptr; > > >>> + > > >>> +/// High-level execution type for ww_mutex. > > >>> +/// > > >>> +/// Tracks a series of locks acquired under a common > > >>> [`WwAcquireCtx`]. +/// It ensures proper cleanup and retry > > >>> mechanism on deadlocks and provides +/// type-safe access to > > >>> locked data via [`with_locked`]. +/// > > >>> +/// Typical usage is through [`lock_all`], which retries a > > >>> user-supplied +/// locking algorithm until it succeeds without > > >>> deadlock. +pub struct ExecContext<'a> { > > >>> + class: &'a WwClass, > > >>> + acquire: Pin>>, > > >>> + taken: KVec>, > > >>> +} > > >>> + > > >>> +impl<'a> Drop for ExecContext<'a> { > > >>> + fn drop(&mut self) { > > >>> + self.release_all_locks(); > > >>=20 > > >> If we move this to the acquire context, then we can do away with > > >> this drop impl. > > >>=20 > > >>> + } > > >>> +} > > >>> + > > >>> +impl<'a> ExecContext<'a> { > > >>> + /// Creates a new [`ExecContext`] for the given lock class. > > >>> + /// > > >>> + /// All locks taken through this context must belong to the > > >>> same class. > > >>> + /// > > >>> + /// TODO: Add some safety mechanism to ensure classes are > > >>> not different. > > >>=20 > > >> core::ptr::eq()? > > >>=20 > > >=20 > > > I was thinking more of a type-level mechanism to do ensure that. > >=20 > > Why? > >=20 >=20 > So that wait-wound and wait-die classes don't get mixed up in the > same `ExecContext` by using type validation at compile time. >=20 > Of course, `core::ptr::eq()` is still useful/required when the classes > are of the same type but not exactly the same value. Maybe we can do > both. >=20 >=20 > Thanks, > Onur I will also look into whether it's possible to remove the class from the mutex and instead derive it from ExecContext and WwAcquireCtx. This would fix both issues at once in a better way. -Onur=20