linux-kernel - [PATCH locking 09/11] rust: sync: condvar: Add wait_interruptible

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Message-ID: <20250307232717.1759087-10-boqun.feng@gmail.com>
Date: Fri,  7 Mar 2025 15:26:59 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>,
	linux-kernel@...r.kernel.org,
	Alice Ryhl <aliceryhl@...gle.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	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>,
	Mitchell Levy <levymitchell0@...il.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	Martin Rodriguez Reboredo <yakoyoku@...il.com>,
	rust-for-linux@...r.kernel.org (open list:RUST)
Subject: [PATCH locking 09/11] rust: sync: condvar: Add wait_interruptible_freezable()

From: Alice Ryhl <aliceryhl@...gle.com>

To support waiting for a `CondVar` as a freezable process, add a
wait_interruptible_freezable() function.

Binder needs this function in the appropriate places to freeze a process
where some of its threads are blocked on the Binder driver.

[Boqun: Capitalize the title, reword the commit log and rephrase the
function doc comment with the impersonal style to align with rest of the
file]

Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Link: https://lore.kernel.org/r/20250204-condvar-freeze-v2-1-804483096260@google.com
---
 rust/kernel/sync/condvar.rs | 23 ++++++++++++++++++++++-
 rust/kernel/task.rs         |  2 ++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index 7df565038d7d..5c1e546a26c3 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -11,7 +11,9 @@
     init::PinInit,
     pin_init,
     str::CStr,
-    task::{MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE},
+    task::{
+        MAX_SCHEDULE_TIMEOUT, TASK_FREEZABLE, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE,
+    },
     time::Jiffies,
     types::Opaque,
 };
@@ -159,6 +161,25 @@ pub fn wait_interruptible<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T,
         crate::current!().signal_pending()
     }
 
+    /// Releases the lock and waits for a notification in interruptible and freezable mode.
+    ///
+    /// The process is allowed to be frozen during this sleep. No lock should be held when calling
+    /// this function, and there is a lockdep assertion for this. Freezing a task that holds a lock
+    /// can trivially deadlock vs another task that needs that lock to complete before it too can
+    /// hit freezable.
+    #[must_use = "wait_interruptible_freezable returns if a signal is pending, so the caller must check the return value"]
+    pub fn wait_interruptible_freezable<T: ?Sized, B: Backend>(
+        &self,
+        guard: &mut Guard<'_, T, B>,
+    ) -> bool {
+        self.wait_internal(
+            TASK_INTERRUPTIBLE | TASK_FREEZABLE,
+            guard,
+            MAX_SCHEDULE_TIMEOUT,
+        );
+        crate::current!().signal_pending()
+    }
+
     /// Releases the lock and waits for a notification in interruptible mode.
     ///
     /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 07bc22a7645c..ea43a3b8d9c5 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -23,6 +23,8 @@
 pub const TASK_INTERRUPTIBLE: c_int = bindings::TASK_INTERRUPTIBLE as c_int;
 /// Bitmask for tasks that are sleeping in an uninterruptible state.
 pub const TASK_UNINTERRUPTIBLE: c_int = bindings::TASK_UNINTERRUPTIBLE as c_int;
+/// Bitmask for tasks that are sleeping in a freezable state.
+pub const TASK_FREEZABLE: c_int = bindings::TASK_FREEZABLE as c_int;
 /// Convenience constant for waking up tasks regardless of whether they are in interruptible or
 /// uninterruptible sleep.
 pub const TASK_NORMAL: c_uint = bindings::TASK_NORMAL as c_uint;
-- 
2.47.1