Commit | Line | Data |
---|---|---|
313c4281 WAF |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | ||
3 | //! Tasks (threads and processes). | |
4 | //! | |
5 | //! C header: [`include/linux/sched.h`](../../../../include/linux/sched.h). | |
6 | ||
7 | use crate::{bindings, types::Opaque}; | |
8da7a2b7 WAF |
8 | use core::{marker::PhantomData, ops::Deref, ptr}; |
9 | ||
10 | /// Returns the currently running task. | |
11 | #[macro_export] | |
12 | macro_rules! current { | |
13 | () => { | |
14 | // SAFETY: Deref + addr-of below create a temporary `TaskRef` that cannot outlive the | |
15 | // caller. | |
16 | unsafe { &*$crate::task::Task::current() } | |
17 | }; | |
18 | } | |
313c4281 WAF |
19 | |
20 | /// Wraps the kernel's `struct task_struct`. | |
21 | /// | |
22 | /// # Invariants | |
23 | /// | |
24 | /// All instances are valid tasks created by the C portion of the kernel. | |
25 | /// | |
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`. | |
8da7a2b7 WAF |
28 | /// |
29 | /// # Examples | |
30 | /// | |
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: | |
33 | /// | |
34 | /// ``` | |
35 | /// let pid = current!().pid(); | |
36 | /// ``` | |
37 | /// | |
38 | /// Getting the PID of the current process, also zero additional cost: | |
39 | /// | |
40 | /// ``` | |
41 | /// let pid = current!().group_leader().pid(); | |
42 | /// ``` | |
43 | /// | |
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: | |
46 | /// | |
47 | /// ``` | |
48 | /// use kernel::{task::Task, types::ARef}; | |
49 | /// | |
50 | /// struct State { | |
51 | /// creator: ARef<Task>, | |
52 | /// index: u32, | |
53 | /// } | |
54 | /// | |
55 | /// impl State { | |
56 | /// fn new() -> Self { | |
57 | /// Self { | |
58 | /// creator: current!().into(), | |
59 | /// index: 0, | |
60 | /// } | |
61 | /// } | |
62 | /// } | |
63 | /// ``` | |
313c4281 WAF |
64 | #[repr(transparent)] |
65 | pub struct Task(pub(crate) Opaque<bindings::task_struct>); | |
66 | ||
d09a6102 AR |
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 {} | |
72 | ||
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 | |
313c4281 WAF |
75 | // synchronised by C code (e.g., `signal_pending`). |
76 | unsafe impl Sync for Task {} | |
77 | ||
78 | /// The type of process identifiers (PIDs). | |
79 | type Pid = bindings::pid_t; | |
80 | ||
81 | impl Task { | |
8da7a2b7 WAF |
82 | /// Returns a task reference for the currently executing task/thread. |
83 | /// | |
84 | /// The recommended way to get the current task/thread is to use the | |
85 | /// [`current`](crate::current) macro because it is safe. | |
86 | /// | |
87 | /// # Safety | |
88 | /// | |
89 | /// Callers must ensure that the returned object doesn't outlive the current task/thread. | |
90 | pub unsafe fn current() -> impl Deref<Target = Task> { | |
91 | struct TaskRef<'a> { | |
92 | task: &'a Task, | |
93 | _not_send: PhantomData<*mut ()>, | |
94 | } | |
95 | ||
96 | impl Deref for TaskRef<'_> { | |
97 | type Target = Task; | |
98 | ||
99 | fn deref(&self) -> &Self::Target { | |
100 | self.task | |
101 | } | |
102 | } | |
103 | ||
104 | // SAFETY: Just an FFI call with no additional safety requirements. | |
105 | let ptr = unsafe { bindings::get_current() }; | |
106 | ||
107 | TaskRef { | |
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, | |
113 | } | |
114 | } | |
115 | ||
313c4281 WAF |
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) }; | |
121 | ||
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() } | |
126 | } | |
127 | ||
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 | |
131 | // have a valid pid. | |
132 | unsafe { *ptr::addr_of!((*self.0.get()).pid) } | |
133 | } | |
134 | ||
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 } | |
139 | } | |
140 | ||
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 | |
145 | // running. | |
146 | unsafe { bindings::wake_up_process(self.0.get()) }; | |
147 | } | |
148 | } | |
149 | ||
150 | // SAFETY: The type invariants guarantee that `Task` is always ref-counted. | |
151 | unsafe impl crate::types::AlwaysRefCounted for Task { | |
152 | fn inc_ref(&self) { | |
153 | // SAFETY: The existence of a shared reference means that the refcount is nonzero. | |
154 | unsafe { bindings::get_task_struct(self.0.get()) }; | |
155 | } | |
156 | ||
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()) } | |
160 | } | |
161 | } |