1 // SPDX-License-Identifier: GPL-2.0
3 //! Tasks (threads and processes).
5 //! C header: [`include/linux/sched.h`](srctree/include/linux/sched.h).
7 use crate::{bindings, types::Opaque};
8 use core::{marker::PhantomData, ops::Deref, ptr};
10 /// Returns the currently running task.
12 macro_rules! current {
14 // SAFETY: Deref + addr-of below create a temporary `TaskRef` that cannot outlive the
16 unsafe { &*$crate::task::Task::current() }
20 /// Wraps the kernel's `struct task_struct`.
24 /// All instances are valid tasks created by the C portion of the kernel.
26 /// Instances of this type are always ref-counted, that is, a call to `get_task_struct` ensures
27 /// that the allocation remains valid at least until the matching call to `put_task_struct`.
31 /// The following is an example of getting the PID of the current thread with zero additional cost
32 /// when compared to the C version:
35 /// let pid = current!().pid();
38 /// Getting the PID of the current process, also zero additional cost:
41 /// let pid = current!().group_leader().pid();
44 /// Getting the current task and storing it in some struct. The reference count is automatically
45 /// incremented when creating `State` and decremented when it is dropped:
48 /// use kernel::{task::Task, types::ARef};
51 /// creator: ARef<Task>,
56 /// fn new() -> Self {
58 /// creator: current!().into(),
65 pub struct Task(pub(crate) Opaque<bindings::task_struct>);
67 // SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
68 // `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
69 // which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
70 // runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
71 unsafe impl Send for Task {}
73 // SAFETY: It's OK to access `Task` through shared references from other threads because we're
74 // either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
75 // synchronised by C code (e.g., `signal_pending`).
76 unsafe impl Sync for Task {}
78 /// The type of process identifiers (PIDs).
79 type Pid = bindings::pid_t;
82 /// Returns a task reference for the currently executing task/thread.
84 /// The recommended way to get the current task/thread is to use the
85 /// [`current`] macro because it is safe.
89 /// Callers must ensure that the returned object doesn't outlive the current task/thread.
90 pub unsafe fn current() -> impl Deref<Target = Task> {
93 _not_send: PhantomData<*mut ()>,
96 impl Deref for TaskRef<'_> {
99 fn deref(&self) -> &Self::Target {
104 // SAFETY: Just an FFI call with no additional safety requirements.
105 let ptr = unsafe { bindings::get_current() };
108 // SAFETY: If the current thread is still running, the current task is valid. Given
109 // that `TaskRef` is not `Send`, we know it cannot be transferred to another thread
110 // (where it could potentially outlive the caller).
111 task: unsafe { &*ptr.cast() },
112 _not_send: PhantomData,
116 /// Returns the group leader of the given task.
117 pub fn group_leader(&self) -> &Task {
118 // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
119 // have a valid group_leader.
120 let ptr = unsafe { *ptr::addr_of!((*self.0.get()).group_leader) };
122 // SAFETY: The lifetime of the returned task reference is tied to the lifetime of `self`,
123 // and given that a task has a reference to its group leader, we know it must be valid for
124 // the lifetime of the returned task reference.
125 unsafe { &*ptr.cast() }
128 /// Returns the PID of the given task.
129 pub fn pid(&self) -> Pid {
130 // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
132 unsafe { *ptr::addr_of!((*self.0.get()).pid) }
135 /// Determines whether the given task has pending signals.
136 pub fn signal_pending(&self) -> bool {
137 // SAFETY: By the type invariant, we know that `self.0` is valid.
138 unsafe { bindings::signal_pending(self.0.get()) != 0 }
141 /// Wakes up the task.
142 pub fn wake_up(&self) {
143 // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid.
144 // And `wake_up_process` is safe to be called for any valid task, even if the task is
146 unsafe { bindings::wake_up_process(self.0.get()) };
150 // SAFETY: The type invariants guarantee that `Task` is always ref-counted.
151 unsafe impl crate::types::AlwaysRefCounted for Task {
153 // SAFETY: The existence of a shared reference means that the refcount is nonzero.
154 unsafe { bindings::get_task_struct(self.0.get()) };
157 unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
158 // SAFETY: The safety requirements guarantee that the refcount is nonzero.
159 unsafe { bindings::put_task_struct(obj.cast().as_ptr()) }