[PATCH v3 09/13] rust: add basic `Task`

Wedson Almeida Filho
2023-04-08T07:55:03Z

From: Wedson Almeida Filho <walmeida@microsoft.com>

It is an abstraction for C's `struct task_struct`. It implements
`AlwaysRefCounted`, so the refcount of the wrapped object is managed
safely on the Rust side.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
v1 -> v2: No changes
v2 -> v3: Wrap task_struct with `Opaque` instead of `UnsafeCell`

rust/bindings/bindings_helper.h | 1 +
rust/helpers.c | 19 +++++++++
rust/kernel/lib.rs | 1 +
rust/kernel/task.rs | 75 +++++++++++++++++++++++++++++++++
4 files changed, 96 insertions(+)
create mode 100644 rust/kernel/task.rs

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 75d85bd6c592..03656a44a83f 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -8,6 +8,7 @@

#include <linux/slab.h>
#include <linux/refcount.h>
+#include <linux/sched.h>

/* `bindgen` gets confused at certain things. */
const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
diff --git a/rust/helpers.c b/rust/helpers.c
index e42f5b446f92..58a194042c86 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -23,6 +23,7 @@
#include <linux/refcount.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
+#include <linux/sched/signal.h>

__noreturn void rust_helper_BUG(void)
{
@@ -75,6 +76,12 @@ void rust_helper_spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
}
EXPORT_SYMBOL_GPL(rust_helper_spin_unlock_irqrestore);

+int rust_helper_signal_pending(struct task_struct *t)
+{
+ return signal_pending(t);
+}
+EXPORT_SYMBOL_GPL(rust_helper_signal_pending);
+
refcount_t rust_helper_REFCOUNT_INIT(int n)
{
return (refcount_t)REFCOUNT_INIT(n);
@@ -93,6 +100,18 @@ bool rust_helper_refcount_dec_and_test(refcount_t *r)
}
EXPORT_SYMBOL_GPL(rust_helper_refcount_dec_and_test);

+void rust_helper_get_task_struct(struct task_struct *t)
+{
+ get_task_struct(t);
+}
+EXPORT_SYMBOL_GPL(rust_helper_get_task_struct);
+
+void rust_helper_put_task_struct(struct task_struct *t)
+{
+ put_task_struct(t);
+}
+EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
+
/*
* We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
* as the Rust `usize` type, so we can use it in contexts where Rust
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 2d7606135ef6..ee27e10da479 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -44,6 +44,7 @@ mod static_assert;
pub mod std_vendor;
pub mod str;
pub mod sync;
+pub mod task;
pub mod types;

#[doc(hidden)]
diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
new file mode 100644
index 000000000000..d70cad131956
--- /dev/null
+++ b/rust/kernel/task.rs
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Tasks (threads and processes).
+//!
+//! C header: [`include/linux/sched.h`](../../../../include/linux/sched.h).
+
+use crate::{bindings, types::Opaque};
+use core::ptr;
+
+/// Wraps the kernel's `struct task_struct`.
+///
+/// # Invariants
+///
+/// All instances are valid tasks created by the C portion of the kernel.
+///
+/// Instances of this type are always ref-counted, that is, a call to `get_task_struct` ensures
+/// that the allocation remains valid at least until the matching call to `put_task_struct`.
+#[repr(transparent)]
+pub struct Task(pub(crate) Opaque<bindings::task_struct>);
+
+// SAFETY: It's OK to access `Task` through references from other threads because we're either
+// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
+// synchronised by C code (e.g., `signal_pending`).
+unsafe impl Sync for Task {}
+
+/// The type of process identifiers (PIDs).
+type Pid = bindings::pid_t;
+
+impl Task {
+ /// Returns the group leader of the given task.
+ pub fn group_leader(&self) -> &Task {
+ // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
+ // have a valid group_leader.
+ let ptr = unsafe { *ptr::addr_of!((*self.0.get()).group_leader) };
+
+ // SAFETY: The lifetime of the returned task reference is tied to the lifetime of `self`,
+ // and given that a task has a reference to its group leader, we know it must be valid for
+ // the lifetime of the returned task reference.
+ unsafe { &*ptr.cast() }
+ }
+
+ /// Returns the PID of the given task.
+ pub fn pid(&self) -> Pid {
+ // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
+ // have a valid pid.
+ unsafe { *ptr::addr_of!((*self.0.get()).pid) }
+ }
+
+ /// Determines whether the given task has pending signals.
+ pub fn signal_pending(&self) -> bool {
+ // SAFETY: By the type invariant, we know that `self.0` is valid.
+ unsafe { bindings::signal_pending(self.0.get()) != 0 }
+ }
+
+ /// Wakes up the task.
+ pub fn wake_up(&self) {
+ // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid.
+ // And `wake_up_process` is safe to be called for any valid task, even if the task is
+ // running.
+ unsafe { bindings::wake_up_process(self.0.get()) };
+ }
+}
+
+// SAFETY: The type invariants guarantee that `Task` is always ref-counted.
+unsafe impl crate::types::AlwaysRefCounted for Task {
+ fn inc_ref(&self) {
+ // SAFETY: The existence of a shared reference means that the refcount is nonzero.
+ unsafe { bindings::get_task_struct(self.0.get()) };
+ }
+
+ unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
+ // SAFETY: The safety requirements guarantee that the refcount is nonzero.
+ unsafe { bindings::put_task_struct(obj.cast().as_ptr()) }
+ }
+}
--
2.34.1