linux-kernel - [POC 0/6] Allow SpinLockIrq to use a normal Guard interface

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Message-ID: <20241018055125.2784186-1-boqun.feng@gmail.com>
Date: Thu, 17 Oct 2024 22:51:19 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: "Thomas Gleixner" <tglx@...utronix.de>
Cc: Dirk Behme <dirk.behme@...il.com>,
	Lyude Paul <lyude@...hat.com>,
	rust-for-linux@...r.kernel.org,
	Danilo Krummrich <dakr@...hat.com>,
	airlied@...hat.com,
	Ingo Molnar <mingo@...hat.com>,
	will@...nel.org,
	Waiman Long <longman@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	wedsonaf@...il.com,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	aliceryhl@...gle.com,
	Trevor Gross <tmgross@...ch.edu>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [POC 0/6] Allow SpinLockIrq to use a normal Guard interface

Hi Thomas,

So this series is what I proposed, previously, because the nested
interrupt API in C is local_irq_save() and local_irq_restore(), the
following Rust code has the problem of enabling interrupt earlier:

	// l1 and l2 are interrupt disabling locks, their guards (i.e.
	// return of lock()) can be used to track interrupt state.

	// interrupts are enabled in the beginning.
	
	let g1 = l1.lock(); // previous interrupt state is enabled.
	let g2 = l2.lock(); // previous interrupt state is disabled.

	drop(g1); // release l1, if we use g1's state, interrupt will be
		  // enabled. But this is obviously wrong. Because g2
		  // can only exist with interrupt disabled.

With the new interrupt disable and enable API, instead of a "unsigned
long", a percpu variable is used to track the outermost interrupt state
and the nested level, so that "drop(g1);" above won't enable interrupts.

Although this requires extra cost, but I think it might be worth paying,
because this could make Rust's SpinLockIrq simply use a guard interface
as SpinLock.

Of course, looking for any comments and suggestions.

Boqun Feng (3):
  irq & spin_lock: Add counted interrupt disabling/enabling
  rust: helper: Add spin_{un,}lock_irq_{enable,disable}() helpers
  rust: sync: lock: Add `Backend::BackendInContext`

Lyude Paul (3):
  rust: Introduce interrupt module
  rust: sync: Add SpinLockIrq
  rust: sync: Introduce lock::Backend::Context

 include/linux/irqflags.h          |  32 +++++++++-
 include/linux/irqflags_types.h    |   6 ++
 include/linux/spinlock.h          |  13 ++++
 include/linux/spinlock_api_smp.h  |  29 +++++++++
 include/linux/spinlock_rt.h       |  10 +++
 kernel/locking/spinlock.c         |  16 +++++
 kernel/softirq.c                  |   3 +
 rust/helpers/helpers.c            |   1 +
 rust/helpers/interrupt.c          |  18 ++++++
 rust/helpers/spinlock.c           |  10 +++
 rust/kernel/interrupt.rs          |  64 +++++++++++++++++++
 rust/kernel/lib.rs                |   1 +
 rust/kernel/sync.rs               |   2 +-
 rust/kernel/sync/lock.rs          |  33 +++++++++-
 rust/kernel/sync/lock/mutex.rs    |   2 +
 rust/kernel/sync/lock/spinlock.rs | 103 ++++++++++++++++++++++++++++++
 16 files changed, 340 insertions(+), 3 deletions(-)
 create mode 100644 rust/helpers/interrupt.c
 create mode 100644 rust/kernel/interrupt.rs

-- 
2.45.2