Commit | Line | Data |
---|---|---|
313c4281 WAF |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | ||
3 | //! Tasks (threads and processes). | |
4 | //! | |
bc2e7d5c | 5 | //! C header: [`include/linux/sched.h`](srctree/include/linux/sched.h). |
313c4281 | 6 | |
00280272 | 7 | use crate::types::Opaque; |
f090f0d0 AR |
8 | use core::{ |
9 | ffi::{c_int, c_long, c_uint}, | |
10 | marker::PhantomData, | |
11 | ops::Deref, | |
12 | ptr, | |
13 | }; | |
e7b9b1ff AR |
14 | |
15 | /// A sentinel value used for infinite timeouts. | |
16 | pub const MAX_SCHEDULE_TIMEOUT: c_long = c_long::MAX; | |
8da7a2b7 | 17 | |
f090f0d0 AR |
18 | /// Bitmask for tasks that are sleeping in an interruptible state. |
19 | pub const TASK_INTERRUPTIBLE: c_int = bindings::TASK_INTERRUPTIBLE as c_int; | |
20 | /// Bitmask for tasks that are sleeping in an uninterruptible state. | |
21 | pub const TASK_UNINTERRUPTIBLE: c_int = bindings::TASK_UNINTERRUPTIBLE as c_int; | |
22 | /// Convenience constant for waking up tasks regardless of whether they are in interruptible or | |
23 | /// uninterruptible sleep. | |
24 | pub const TASK_NORMAL: c_uint = bindings::TASK_NORMAL as c_uint; | |
25 | ||
8da7a2b7 WAF |
26 | /// Returns the currently running task. |
27 | #[macro_export] | |
28 | macro_rules! current { | |
29 | () => { | |
30 | // SAFETY: Deref + addr-of below create a temporary `TaskRef` that cannot outlive the | |
31 | // caller. | |
32 | unsafe { &*$crate::task::Task::current() } | |
33 | }; | |
34 | } | |
313c4281 WAF |
35 | |
36 | /// Wraps the kernel's `struct task_struct`. | |
37 | /// | |
38 | /// # Invariants | |
39 | /// | |
40 | /// All instances are valid tasks created by the C portion of the kernel. | |
41 | /// | |
ebf2b8a7 | 42 | /// Instances of this type are always refcounted, that is, a call to `get_task_struct` ensures |
313c4281 | 43 | /// that the allocation remains valid at least until the matching call to `put_task_struct`. |
8da7a2b7 WAF |
44 | /// |
45 | /// # Examples | |
46 | /// | |
47 | /// The following is an example of getting the PID of the current thread with zero additional cost | |
48 | /// when compared to the C version: | |
49 | /// | |
50 | /// ``` | |
51 | /// let pid = current!().pid(); | |
52 | /// ``` | |
53 | /// | |
54 | /// Getting the PID of the current process, also zero additional cost: | |
55 | /// | |
56 | /// ``` | |
57 | /// let pid = current!().group_leader().pid(); | |
58 | /// ``` | |
59 | /// | |
60 | /// Getting the current task and storing it in some struct. The reference count is automatically | |
61 | /// incremented when creating `State` and decremented when it is dropped: | |
62 | /// | |
63 | /// ``` | |
64 | /// use kernel::{task::Task, types::ARef}; | |
65 | /// | |
66 | /// struct State { | |
67 | /// creator: ARef<Task>, | |
68 | /// index: u32, | |
69 | /// } | |
70 | /// | |
71 | /// impl State { | |
72 | /// fn new() -> Self { | |
73 | /// Self { | |
74 | /// creator: current!().into(), | |
75 | /// index: 0, | |
76 | /// } | |
77 | /// } | |
78 | /// } | |
79 | /// ``` | |
313c4281 WAF |
80 | #[repr(transparent)] |
81 | pub struct Task(pub(crate) Opaque<bindings::task_struct>); | |
82 | ||
d09a6102 AR |
83 | // SAFETY: By design, the only way to access a `Task` is via the `current` function or via an |
84 | // `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in | |
85 | // which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor | |
86 | // runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`. | |
87 | unsafe impl Send for Task {} | |
88 | ||
89 | // SAFETY: It's OK to access `Task` through shared references from other threads because we're | |
90 | // either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly | |
313c4281 WAF |
91 | // synchronised by C code (e.g., `signal_pending`). |
92 | unsafe impl Sync for Task {} | |
93 | ||
94 | /// The type of process identifiers (PIDs). | |
95 | type Pid = bindings::pid_t; | |
96 | ||
97 | impl Task { | |
8da7a2b7 WAF |
98 | /// Returns a task reference for the currently executing task/thread. |
99 | /// | |
100 | /// The recommended way to get the current task/thread is to use the | |
c61bcc27 | 101 | /// [`current`] macro because it is safe. |
8da7a2b7 WAF |
102 | /// |
103 | /// # Safety | |
104 | /// | |
105 | /// Callers must ensure that the returned object doesn't outlive the current task/thread. | |
106 | pub unsafe fn current() -> impl Deref<Target = Task> { | |
107 | struct TaskRef<'a> { | |
108 | task: &'a Task, | |
109 | _not_send: PhantomData<*mut ()>, | |
110 | } | |
111 | ||
112 | impl Deref for TaskRef<'_> { | |
113 | type Target = Task; | |
114 | ||
115 | fn deref(&self) -> &Self::Target { | |
116 | self.task | |
117 | } | |
118 | } | |
119 | ||
120 | // SAFETY: Just an FFI call with no additional safety requirements. | |
121 | let ptr = unsafe { bindings::get_current() }; | |
122 | ||
123 | TaskRef { | |
124 | // SAFETY: If the current thread is still running, the current task is valid. Given | |
125 | // that `TaskRef` is not `Send`, we know it cannot be transferred to another thread | |
126 | // (where it could potentially outlive the caller). | |
127 | task: unsafe { &*ptr.cast() }, | |
128 | _not_send: PhantomData, | |
129 | } | |
130 | } | |
131 | ||
313c4281 WAF |
132 | /// Returns the group leader of the given task. |
133 | pub fn group_leader(&self) -> &Task { | |
134 | // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always | |
af8b18d7 | 135 | // have a valid `group_leader`. |
313c4281 WAF |
136 | let ptr = unsafe { *ptr::addr_of!((*self.0.get()).group_leader) }; |
137 | ||
138 | // SAFETY: The lifetime of the returned task reference is tied to the lifetime of `self`, | |
139 | // and given that a task has a reference to its group leader, we know it must be valid for | |
140 | // the lifetime of the returned task reference. | |
141 | unsafe { &*ptr.cast() } | |
142 | } | |
143 | ||
144 | /// Returns the PID of the given task. | |
145 | pub fn pid(&self) -> Pid { | |
146 | // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always | |
147 | // have a valid pid. | |
148 | unsafe { *ptr::addr_of!((*self.0.get()).pid) } | |
149 | } | |
150 | ||
151 | /// Determines whether the given task has pending signals. | |
152 | pub fn signal_pending(&self) -> bool { | |
153 | // SAFETY: By the type invariant, we know that `self.0` is valid. | |
154 | unsafe { bindings::signal_pending(self.0.get()) != 0 } | |
155 | } | |
156 | ||
157 | /// Wakes up the task. | |
158 | pub fn wake_up(&self) { | |
159 | // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid. | |
160 | // And `wake_up_process` is safe to be called for any valid task, even if the task is | |
161 | // running. | |
162 | unsafe { bindings::wake_up_process(self.0.get()) }; | |
163 | } | |
164 | } | |
165 | ||
ebf2b8a7 | 166 | // SAFETY: The type invariants guarantee that `Task` is always refcounted. |
313c4281 WAF |
167 | unsafe impl crate::types::AlwaysRefCounted for Task { |
168 | fn inc_ref(&self) { | |
169 | // SAFETY: The existence of a shared reference means that the refcount is nonzero. | |
170 | unsafe { bindings::get_task_struct(self.0.get()) }; | |
171 | } | |
172 | ||
173 | unsafe fn dec_ref(obj: ptr::NonNull<Self>) { | |
174 | // SAFETY: The safety requirements guarantee that the refcount is nonzero. | |
175 | unsafe { bindings::put_task_struct(obj.cast().as_ptr()) } | |
176 | } | |
177 | } |