From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f41.google.com (mail-wm1-f41.google.com [209.85.128.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 35BFA54FAD for ; Fri, 13 Sep 2024 16:02:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726243326; cv=none; b=so4umdBeg9MKZWAK+4+Zgi5rbr275SbDLu+dwT9vae03rQVeoSAD8Gf3sva0EOWZcKyYI3HCwozp98TNxVVY2Xo/3V7YguJ7zHtLZFRfxPdsb2MpzqesrXlAWjUOeMiw+i1UOmtMAY4F3U3AkRdz2HiOv133XWXQSl87t9mjPDg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726243326; c=relaxed/simple; bh=K/mhLJMvEunhzXXiJGi7I4liWcDDWB1oFDZjpS7m/1U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YmCKdspvLPgzz58lKoZ79vRSJBsCUle6ONzOZZ+yO+dhs7JFjZ+MBSTb4D9pT/Ys5Nj9Wx0k9RjGVOurF/DTlX94EfsOnM9/01/0Rs4r2Ll2vREpLurfzdbz1Ddxh/6voFLMBpUVjzkfutDFQWm9Yl+i00+M76Mq2qrEuV7MKsM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch; spf=none smtp.mailfrom=ffwll.ch; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b=YJc0Miu9; arc=none smtp.client-ip=209.85.128.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ffwll.ch Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="YJc0Miu9" Received: by mail-wm1-f41.google.com with SMTP id 5b1f17b1804b1-42cc43454d5so9970535e9.3 for ; Fri, 13 Sep 2024 09:02:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; t=1726243322; x=1726848122; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references :mail-followup-to:message-id:subject:cc:to:from:date:from:to:cc :subject:date:message-id:reply-to; bh=ucXoPNM5iv3Z48KoYnoRdXBOJh2joZhrnD0xMJKeank=; b=YJc0Miu9xw5h331yoGJkkg2TvwQi8OApfCuq83cloj4+rFhJIKW+4ml1lnIXnPo8Ow M3Xv536g90S0W/6INvD0tEqggaH7EvZ2UswNW8A/ZlmyoJXDQ68GJuzwO8B635+IGRlN wVgxTrMA0yoffrNNygMA5IYpT1mOi/FOw5a0c= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1726243322; x=1726848122; h=in-reply-to:content-disposition:mime-version:references :mail-followup-to:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=ucXoPNM5iv3Z48KoYnoRdXBOJh2joZhrnD0xMJKeank=; b=K0+vydD8Ql8zk/pAzVLHfIfxMe3fI8BRk3j62Y7/iE986cr6K2XuT/bxUAH4bUExsz ZPqBIgSi9dQIHJHTYKHyG0PRHkcsuRliwf6hSDMWYPBjfEWUJtm+7w1xYsi52Eu+bw9A Ga2XDzyJFwRghGDKPkoM0H2LzBttbYVcajFHbx4FOOISdlUBPIyhX2c8DnIGb8jfQGKG ltzNmh3XQBDfhPWzbSEctvFr4jQlHzCB8yesA0uP/4MDGlCoi44Yr2Rt8DhBA54gqxMp 2rMWtIyOCMAKKq0o7OIA6+POjgJc42soJ3fQTTmOhcO9Qg4Ze8Oc9iUBpprhrP1pFzDY pE4g== X-Forwarded-Encrypted: i=1; AJvYcCWmmUnqU2Wmk4BAtO7XRX4IKpPLxpP5a8qwpW7sG3Gr+nEQm8nhFqDphi55ZViUQO5kt+nihZxVm0Ytltt0Fw==@vger.kernel.org X-Gm-Message-State: AOJu0YwYBuYdFyhQOuO+xBlXOwkn9W7AWfXZ8NCP/XkwrPbOyLjOOwch aySuVXtdC2LgO+AWQ6N3+TIGjcZ9cP2V92tOzXVv/wUKH1c4KQqu5hCW5s0nILY= X-Google-Smtp-Source: AGHT+IHQUhB1vBWL4HY6/Iwwa8tGpvaiq4QI+ygJWY509coLxHJRlQfjU4LUgCLAmRnuO4nujPiNfQ== X-Received: by 2002:a05:600c:1d17:b0:42b:a7c7:5667 with SMTP id 5b1f17b1804b1-42d964d8563mr25882725e9.25.1726243321922; Fri, 13 Sep 2024 09:02:01 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:5485:d4b2:c087:b497]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42d9b054f97sm30579215e9.4.2024.09.13.09.02.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Sep 2024 09:02:00 -0700 (PDT) Date: Fri, 13 Sep 2024 18:01:58 +0200 From: Simona Vetter To: Alice Ryhl Cc: Miguel Ojeda , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] rust: add global lock support Message-ID: Mail-Followup-To: Alice Ryhl , Miguel Ojeda , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240910-static-mutex-v3-1-5bebd11bdf3b@google.com> 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=us-ascii Content-Disposition: inline In-Reply-To: <20240910-static-mutex-v3-1-5bebd11bdf3b@google.com> X-Operating-System: Linux phenom 6.9.12-amd64 On Tue, Sep 10, 2024 at 02:23:34PM +0000, Alice Ryhl wrote: > Add support for creating global variables that are wrapped in a mutex or > spinlock. Optionally, the macro can generate a special LockedBy type > that does not require a runtime check. > > The implementation here is intended to replace the global mutex > workaround found in the Rust Binder RFC [1]. In both cases, the global > lock must be initialized before first use. The macro is unsafe to use > for the same reason. > > The separate initialization step is required because bindgen refuses to > expose __ARCH_SPIN_LOCK_UNLOCKED to Rust as a compile-time constant. It > just generates an `extern "C"` global reference instead. In the future, > we could expose the value of __ARCH_SPIN_LOCK_UNLOCKED to Rust in a way > that Rust can understand. This would remove the need for a separate > initialization step. Yeah it's just a raw C struct initializer, I wouldn't even know how to move that to rust. An absolute horrible idea, and I didn't try whether it's even possible: - put all the global locks of a type into a special linker section (we need a macro anyway for them). - patch them up with a horrible linker script objtool patching with an example lock initialized by the C macro. Even worse idea, on most architectures/config it's all zeros. Iirc the one I've found that might matter a bit is CONFIG_SMP=n with some lock debugging enabled. We could make rust support conditional on those, and then maybe a build-time check that it's actually all set to 0 ... Requiring the unsafe init just feels a bit disappointing to me, when the C side (including lockdep annotations) tries really hard to make global locks a one-liner. Cheers, Sima > > Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-2-08ba9197f637@google.com/#Z31drivers:android:context.rs [1] > Signed-off-by: Alice Ryhl > --- > I've been having some trouble with the kunit tests. The import of > __static_lock_ty_$name fails when I try with kunit, but copying the same > code into a sample does not reproduce the error. Suggestions would be > appreciated. > --- > Changes in v3: > - Rewrite to provide a macro instead. > - Link to v2: https://lore.kernel.org/r/20240827-static-mutex-v2-1-17fc32b20332@google.com > > Changes in v2: > - Require `self: Pin<&Self>` and recommend `Pin::static_ref`. > - Other doc improvements including new example. > - Link to v1: https://lore.kernel.org/r/20240826-static-mutex-v1-1-a14ee71561f3@google.com > --- > rust/kernel/sync.rs | 1 + > rust/kernel/sync/lock.rs | 31 +++++- > rust/kernel/sync/lock/global.rs | 237 ++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 268 insertions(+), 1 deletion(-) > > diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs > index 0ab20975a3b5..2e97e22715db 100644 > --- a/rust/kernel/sync.rs > +++ b/rust/kernel/sync.rs > @@ -14,6 +14,7 @@ > > pub use arc::{Arc, ArcBorrow, UniqueArc}; > pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult}; > +pub use lock::global::global_lock; > pub use lock::mutex::{new_mutex, Mutex}; > pub use lock::spinlock::{new_spinlock, SpinLock}; > pub use locked_by::LockedBy; > diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs > index f6c34ca4d819..3ae7a278016d 100644 > --- a/rust/kernel/sync/lock.rs > +++ b/rust/kernel/sync/lock.rs > @@ -7,12 +7,14 @@ > > use super::LockClassKey; > use crate::{init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard}; > -use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned}; > +use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned, pin::Pin}; > use macros::pin_data; > > pub mod mutex; > pub mod spinlock; > > +pub(super) mod global; > + > /// The "backend" of a lock. > /// > /// It is the actual implementation of the lock, without the need to repeat patterns used in all > @@ -117,6 +119,33 @@ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinIni > }), > }) > } > + > + /// # Safety > + /// > + /// Before any other method on this lock is called, `global_lock_helper_init` must be called. > + #[doc(hidden)] > + pub const unsafe fn global_lock_helper_new(state: Opaque, data: T) -> Self { > + Self { > + state, > + data: UnsafeCell::new(data), > + _pin: PhantomPinned, > + } > + } > + > + /// # Safety > + /// > + /// * This lock must have been created using `global_lock_helper_new`. > + /// * Must only be called once for each lock. > + #[doc(hidden)] > + pub unsafe fn global_lock_helper_init( > + self: Pin<&Self>, > + name: &'static CStr, > + key: &'static LockClassKey, > + ) { > + // SAFETY: The pointer to `state` is valid for the duration of this call, and both `name` > + // and `key` are valid indefinitely. > + unsafe { B::init(self.state.get(), name.as_char_ptr(), key.as_ptr()) } > + } > } > > impl Lock { > diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs > new file mode 100644 > index 000000000000..c1eb25d37abd > --- /dev/null > +++ b/rust/kernel/sync/lock/global.rs > @@ -0,0 +1,237 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +// Copyright (C) 2024 Google LLC. > + > +//! Support for defining statics containing locks. > + > +/// Defines a global lock. > +/// > +/// Supports the following options: > +/// > +/// * `value` specifies the initial value in the global lock. > +/// * `wrapper` specifies the name of the wrapper struct. > +/// * `guard` specifies the name of the guard type. > +/// * `locked_by` specifies the name of the `LockedBy` type. > +/// > +/// # Examples > +/// > +/// A global counter. > +/// > +/// ``` > +/// kernel::sync::global_lock! { > +/// // SAFETY: Initialized in module initializer before first use. > +/// static MY_COUNTER: Mutex = unsafe { uninit }; > +/// value: 0; > +/// } > +/// > +/// fn increment_counter() -> u32 { > +/// let mut guard = MY_COUNTER.lock(); > +/// *guard += 1; > +/// *guard > +/// } > +/// > +/// impl kernel::Module for MyModule { > +/// fn init(_module: &'static ThisModule) -> Result { > +/// // SAFETY: called exactly once > +/// unsafe { MY_COUNTER.init() }; > +/// > +/// Ok(MyModule {}) > +/// } > +/// } > +/// # struct MyModule {} > +/// ``` > +/// > +/// A global mutex used to protect all instances of a given struct. > +/// > +/// ``` > +/// kernel::sync::global_lock! { > +/// // SAFETY: Initialized in module initializer before first use. > +/// static MY_MUTEX: Mutex<()> = unsafe { uninit }; > +/// value: (); > +/// guard: MyGuard; > +/// locked_by: LockedByMyMutex; > +/// } > +/// > +/// /// All instances of this struct are protected by `MY_MUTEX`. > +/// struct MyStruct { > +/// my_counter: LockedByMyMutex, > +/// } > +/// > +/// impl MyStruct { > +/// /// Increment the counter in this instance. > +/// /// > +/// /// The caller must hold the `MY_MUTEX` mutex. > +/// fn increment(&self, guard: &mut MyGuard) -> u32 { > +/// let my_counter = self.my_counter.as_mut(guard); > +/// *my_counter += 1; > +/// *my_counter > +/// } > +/// } > +/// > +/// impl kernel::Module for MyModule { > +/// fn init(_module: &'static ThisModule) -> Result { > +/// // SAFETY: called exactly once > +/// unsafe { MY_MUTEX.init() }; > +/// > +/// Ok(MyModule {}) > +/// } > +/// } > +/// # struct MyModule {} > +/// ``` > +#[macro_export] > +macro_rules! global_lock { > + { > + $(#[$meta:meta])* $pub:vis static $name:ident: $kind:ident<$valuety:ty> = unsafe { uninit }; > + value: $value:expr; > + wrapper: $wrapper:ident; > + $( name: $lname:literal; )? > + $( > + guard: $guard:ident; > + locked_by: $locked_by:ident; > + )? > + } => { > + $crate::macros::paste! { > + type [< __static_lock_ty_ $name >] = $valuety; > + > + #[allow(unused_pub)] > + mod [< __static_lock_mod_ $name >] { > + use super::[< __static_lock_ty_ $name >] as Val; > + type Backend = $crate::global_lock_inner!(backend $kind); > + type GuardTyp = $crate::global_lock_inner!(guard $kind, Val $(, $guard)?); > + > + /// # Safety > + /// > + /// Must be used to initialize `super::$name`. > + pub(super) const unsafe fn new() -> $wrapper { > + let state = $crate::types::Opaque::uninit(); > + $wrapper { > + // SAFETY: The user of this macro promises to call `init` before calling > + // `lock`. > + inner: unsafe { > + $crate::sync::lock::Lock::global_lock_helper_new(state, $value) > + } > + } > + } > + > + /// Wrapper type for a global lock. > + pub struct $wrapper { > + inner: $crate::sync::lock::Lock, > + } > + > + impl $wrapper { > + /// Initialize the global lock. > + /// > + /// # Safety > + /// > + /// This method must not be called more than once. > + pub unsafe fn init(&'static self) { > + // SAFETY: > + // * This type can only be created by `new`. > + // * Caller promises to not call this method more than once. > + unsafe { > + $crate::sync::lock::Lock::global_lock_helper_init( > + ::core::pin::Pin::static_ref(&self.inner), > + $crate::optional_name!($($lname)?), > + $crate::static_lock_class!(), > + ); > + } > + } > + > + /// Lock this global lock. > + pub fn lock(&'static self) -> GuardTyp { > + $crate::global_lock_inner!(new_guard $($guard)? { > + self.inner.lock() > + }) > + } > + } > + > + $( > + pub struct $guard($crate::sync::lock::Guard<'static, Val, Backend>); > + > + impl ::core::ops::Deref for $guard { > + type Target = Val; > + fn deref(&self) -> &Val { > + &self.0 > + } > + } > + > + impl ::core::ops::DerefMut for $guard { > + fn deref_mut(&mut self) -> &mut Val { > + &mut self.0 > + } > + } > + > + pub struct $locked_by(::core::cell::UnsafeCell); > + > + impl $locked_by { > + pub fn new(val: T) -> Self { > + Self(::core::cell::UnsafeCell::new(val)) > + } > + } > + > + impl $locked_by { > + pub fn as_ref<'a>(&'a self, _guard: &'a $guard) -> &'a T { > + // SAFETY: The lock is globally unique, so there can only be one guard. > + unsafe { &*self.0.get() } > + } > + > + pub fn as_mut<'a>(&'a self, _guard: &'a mut $guard) -> &'a mut T { > + // SAFETY: The lock is globally unique, so there can only be one guard. > + unsafe { &mut *self.0.get() } > + } > + > + pub fn get_mut(&mut self) -> &mut T { > + self.0.get_mut() > + } > + } > + )? > + } > + > + use [< __static_lock_mod_ $name >]::$wrapper; > + $( use [< __static_lock_mod_ $name >]::{$guard, $locked_by}; )? > + > + $(#[$meta])* > + $pub static $name: $wrapper = { > + // SAFETY: We are using this to initialize $name. > + unsafe { [< __static_lock_mod_ $name >]::new() } > + }; > + } > + }; > + > + { > + $(#[$meta:meta])* $pub:vis static $name:ident: $kind:ident<$valuety:ty> = unsafe { uninit }; > + value: $value:expr; > + $( name: $lname:literal; )? > + $( > + guard: $guard:ident; > + locked_by: $locked_by:ident; > + )? > + } => { > + $crate::macros::paste! { > + $crate::global_lock! { > + $(#[$meta])* $pub static $name: $kind<$valuety> = unsafe { uninit }; > + value: $value; > + wrapper: [< __static_lock_wrapper_ $name >]; > + $( name: $lname; )? > + $( guard: $guard; locked_by: $locked_by; )? > + } > + } > + } > +} > +pub use global_lock; > + > +#[doc(hidden)] > +#[macro_export] > +macro_rules! global_lock_inner { > + (backend Mutex) => { $crate::sync::lock::mutex::MutexBackend }; > + (backend SpinLock) => { $crate::sync::lock::spinlock::SpinLockBackend }; > + (guard Mutex, $val:ty) => { > + $crate::sync::lock::Guard<'static, $val, $crate::sync::lock::mutex::MutexBackend> > + }; > + (guard SpinLock, $val:ty) => { > + $crate::sync::lock::Guard<'static, $val, $crate::sync::lock::spinlock::SpinLockBackend> > + }; > + (guard $kind:ident, $val:ty, $name:ident) => { $name }; > + (new_guard { $val:expr }) => { $val }; > + (new_guard $name:ident { $val:expr }) => { $name($val) }; > +} > > --- > base-commit: 93dc3be19450447a3a7090bd1dfb9f3daac3e8d2 > change-id: 20240826-static-mutex-a4b228e0e6aa > > Best regards, > -- > Alice Ryhl > -- Simona Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch