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1// SPDX-License-Identifier: GPL-2.0
2
3//! Tasks (threads and processes).
4//!
5//! C header: [`include/linux/sched.h`](srctree/include/linux/sched.h).
6
7use crate::{
8 bindings,
9 mm::MmWithUser,
10 pid_namespace::PidNamespace,
11 prelude::*,
12 sync::aref::ARef,
13 types::{NotThreadSafe, Opaque},
14};
15use core::{
16 ops::Deref,
17 ptr, //
18};
19
20/// A sentinel value used for infinite timeouts.
21pub const MAX_SCHEDULE_TIMEOUT: c_long = c_long::MAX;
22
23/// Bitmask for tasks that are sleeping in an interruptible state.
24pub const TASK_INTERRUPTIBLE: c_int = bindings::TASK_INTERRUPTIBLE as c_int;
25/// Bitmask for tasks that are sleeping in an uninterruptible state.
26pub const TASK_UNINTERRUPTIBLE: c_int = bindings::TASK_UNINTERRUPTIBLE as c_int;
27/// Bitmask for tasks that are sleeping in a freezable state.
28pub const TASK_FREEZABLE: c_int = bindings::TASK_FREEZABLE as c_int;
29/// Convenience constant for waking up tasks regardless of whether they are in interruptible or
30/// uninterruptible sleep.
31pub const TASK_NORMAL: c_uint = bindings::TASK_NORMAL as c_uint;
32
33/// Returns the currently running task.
34#[macro_export]
35macro_rules! current {
36 () => {
37 // SAFETY: This expression creates a temporary value that is dropped at the end of the
38 // caller's scope. The following mechanisms ensure that the resulting `&CurrentTask` cannot
39 // leave current task context:
40 //
41 // * To return to userspace, the caller must leave the current scope.
42 // * Operations such as `begin_new_exec()` are necessarily unsafe and the caller of
43 // `begin_new_exec()` is responsible for safety.
44 // * Rust abstractions for things such as a `kthread_use_mm()` scope must require the
45 // closure to be `Send`, so the `NotThreadSafe` field of `CurrentTask` ensures that the
46 // `&CurrentTask` cannot cross the scope in either direction.
47 unsafe { &*$crate::task::Task::current() }
48 };
49}
50
51/// Wraps the kernel's `struct task_struct`.
52///
53/// # Invariants
54///
55/// All instances are valid tasks created by the C portion of the kernel.
56///
57/// Instances of this type are always refcounted, that is, a call to `get_task_struct` ensures
58/// that the allocation remains valid at least until the matching call to `put_task_struct`.
59///
60/// # Examples
61///
62/// The following is an example of getting the PID of the current thread with zero additional cost
63/// when compared to the C version:
64///
65/// ```
66/// let pid = current!().pid();
67/// ```
68///
69/// Getting the PID of the current process, also zero additional cost:
70///
71/// ```
72/// let pid = current!().group_leader().pid();
73/// ```
74///
75/// Getting the current task and storing it in some struct. The reference count is automatically
76/// incremented when creating `State` and decremented when it is dropped:
77///
78/// ```
79/// use kernel::{task::Task, sync::aref::ARef};
80///
81/// struct State {
82/// creator: ARef<Task>,
83/// index: u32,
84/// }
85///
86/// impl State {
87/// fn new() -> Self {
88/// Self {
89/// creator: ARef::from(&**current!()),
90/// index: 0,
91/// }
92/// }
93/// }
94/// ```
95#[repr(transparent)]
96pub struct Task(pub(crate) Opaque<bindings::task_struct>);
97
98// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
99// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
100// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
101// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
102unsafe impl Send for Task {}
103
104// SAFETY: It's OK to access `Task` through shared references from other threads because we're
105// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
106// synchronised by C code (e.g., `signal_pending`).
107unsafe impl Sync for Task {}
108
109/// Represents the [`Task`] in the `current` global.
110///
111/// This type exists to provide more efficient operations that are only valid on the current task.
112/// For example, to retrieve the pid-namespace of a task, you must use rcu protection unless it is
113/// the current task.
114///
115/// # Invariants
116///
117/// Each value of this type must only be accessed from the task context it was created within.
118///
119/// Of course, every thread is in a different task context, but for the purposes of this invariant,
120/// these operations also permanently leave the task context:
121///
122/// * Returning to userspace from system call context.
123/// * Calling `release_task()`.
124/// * Calling `begin_new_exec()` in a binary format loader.
125///
126/// Other operations temporarily create a new sub-context:
127///
128/// * Calling `kthread_use_mm()` creates a new context, and `kthread_unuse_mm()` returns to the
129/// old context.
130///
131/// This means that a `CurrentTask` obtained before a `kthread_use_mm()` call may be used again
132/// once `kthread_unuse_mm()` is called, but it must not be used between these two calls.
133/// Conversely, a `CurrentTask` obtained between a `kthread_use_mm()`/`kthread_unuse_mm()` pair
134/// must not be used after `kthread_unuse_mm()`.
135#[repr(transparent)]
136pub struct CurrentTask(Task, NotThreadSafe);
137
138// Make all `Task` methods available on `CurrentTask`.
139impl Deref for CurrentTask {
140 type Target = Task;
141 #[inline]
142 fn deref(&self) -> &Task {
143 &self.0
144 }
145}
146
147/// The type of process identifiers (PIDs).
148pub type Pid = bindings::pid_t;
149
150/// The type of user identifiers (UIDs).
151#[derive(Copy, Clone)]
152pub struct Kuid {
153 kuid: bindings::kuid_t,
154}
155
156impl Task {
157 /// Returns a raw pointer to the current task.
158 ///
159 /// It is up to the user to use the pointer correctly.
160 #[inline]
161 pub fn current_raw() -> *mut bindings::task_struct {
162 // SAFETY: Getting the current pointer is always safe.
163 unsafe { bindings::get_current() }
164 }
165
166 /// Returns a task reference for the currently executing task/thread.
167 ///
168 /// The recommended way to get the current task/thread is to use the
169 /// [`current`] macro because it is safe.
170 ///
171 /// # Safety
172 ///
173 /// Callers must ensure that the returned object is only used to access a [`CurrentTask`]
174 /// within the task context that was active when this function was called. For more details,
175 /// see the invariants section for [`CurrentTask`].
176 #[inline]
177 pub unsafe fn current() -> impl Deref<Target = CurrentTask> {
178 struct TaskRef {
179 task: *const CurrentTask,
180 }
181
182 impl Deref for TaskRef {
183 type Target = CurrentTask;
184
185 fn deref(&self) -> &Self::Target {
186 // SAFETY: The returned reference borrows from this `TaskRef`, so it cannot outlive
187 // the `TaskRef`, which the caller of `Task::current()` has promised will not
188 // outlive the task/thread for which `self.task` is the `current` pointer. Thus, it
189 // is okay to return a `CurrentTask` reference here.
190 unsafe { &*self.task }
191 }
192 }
193
194 TaskRef {
195 // CAST: The layout of `struct task_struct` and `CurrentTask` is identical.
196 task: Task::current_raw().cast(),
197 }
198 }
199
200 /// Returns a raw pointer to the task.
201 #[inline]
202 pub fn as_ptr(&self) -> *mut bindings::task_struct {
203 self.0.get()
204 }
205
206 /// Returns the PID of the given task.
207 pub fn pid(&self) -> Pid {
208 // SAFETY: The pid of a task never changes after initialization, so reading this field is
209 // not a data race.
210 unsafe { *ptr::addr_of!((*self.as_ptr()).pid) }
211 }
212
213 /// Returns the TGID (Thread Group ID / Process ID) of the given task.
214 pub fn tgid(&self) -> Pid {
215 // SAFETY: The tgid of a task never changes after initialization, so reading this field is
216 // not a data race.
217 unsafe { *ptr::addr_of!((*self.as_ptr()).tgid) }
218 }
219
220 /// Returns the objective real UID of the given task.
221 #[inline]
222 pub fn uid(&self) -> Kuid {
223 // SAFETY: It's always safe to call `task_uid` on a valid task.
224 Kuid::from_raw(unsafe { bindings::task_uid(self.as_ptr()) })
225 }
226
227 /// Determines whether the given task has pending signals.
228 #[inline]
229 pub fn signal_pending(&self) -> bool {
230 // SAFETY: It's always safe to call `signal_pending` on a valid task.
231 unsafe { bindings::signal_pending(self.as_ptr()) != 0 }
232 }
233
234 /// Returns task's pid namespace with elevated reference count
235 #[inline]
236 pub fn get_pid_ns(&self) -> Option<ARef<PidNamespace>> {
237 // SAFETY: By the type invariant, we know that `self.0` is valid.
238 let ptr = unsafe { bindings::task_get_pid_ns(self.as_ptr()) };
239 if ptr.is_null() {
240 None
241 } else {
242 // SAFETY: `ptr` is valid by the safety requirements of this function. And we own a
243 // reference count via `task_get_pid_ns()`.
244 // CAST: `Self` is a `repr(transparent)` wrapper around `bindings::pid_namespace`.
245 Some(unsafe { ARef::from_raw(ptr::NonNull::new_unchecked(ptr.cast::<PidNamespace>())) })
246 }
247 }
248
249 /// Returns the given task's pid in the provided pid namespace.
250 #[doc(alias = "task_tgid_nr_ns")]
251 #[inline]
252 pub fn tgid_nr_ns(&self, pidns: Option<&PidNamespace>) -> Pid {
253 let pidns = match pidns {
254 Some(pidns) => pidns.as_ptr(),
255 None => core::ptr::null_mut(),
256 };
257 // SAFETY: By the type invariant, we know that `self.0` is valid. We received a valid
258 // PidNamespace that we can use as a pointer or we received an empty PidNamespace and
259 // thus pass a null pointer. The underlying C function is safe to be used with NULL
260 // pointers.
261 unsafe { bindings::task_tgid_nr_ns(self.as_ptr(), pidns) }
262 }
263
264 /// Wakes up the task.
265 #[inline]
266 pub fn wake_up(&self) {
267 // SAFETY: It's always safe to call `wake_up_process` on a valid task, even if the task
268 // running.
269 unsafe { bindings::wake_up_process(self.as_ptr()) };
270 }
271}
272
273impl CurrentTask {
274 /// Access the address space of the current task.
275 ///
276 /// This function does not touch the refcount of the mm.
277 #[inline]
278 pub fn mm(&self) -> Option<&MmWithUser> {
279 // SAFETY: The `mm` field of `current` is not modified from other threads, so reading it is
280 // not a data race.
281 let mm = unsafe { (*self.as_ptr()).mm };
282
283 if mm.is_null() {
284 return None;
285 }
286
287 // SAFETY: If `current->mm` is non-null, then it references a valid mm with a non-zero
288 // value of `mm_users`. Furthermore, the returned `&MmWithUser` borrows from this
289 // `CurrentTask`, so it cannot escape the scope in which the current pointer was obtained.
290 //
291 // This is safe even if `kthread_use_mm()`/`kthread_unuse_mm()` are used. There are two
292 // relevant cases:
293 // * If the `&CurrentTask` was created before `kthread_use_mm()`, then it cannot be
294 // accessed during the `kthread_use_mm()`/`kthread_unuse_mm()` scope due to the
295 // `NotThreadSafe` field of `CurrentTask`.
296 // * If the `&CurrentTask` was created within a `kthread_use_mm()`/`kthread_unuse_mm()`
297 // scope, then the `&CurrentTask` cannot escape that scope, so the returned `&MmWithUser`
298 // also cannot escape that scope.
299 // In either case, it's not possible to read `current->mm` and keep using it after the
300 // scope is ended with `kthread_unuse_mm()`.
301 Some(unsafe { MmWithUser::from_raw(mm) })
302 }
303
304 /// Access the pid namespace of the current task.
305 ///
306 /// This function does not touch the refcount of the namespace or use RCU protection.
307 ///
308 /// To access the pid namespace of another task, see [`Task::get_pid_ns`].
309 #[doc(alias = "task_active_pid_ns")]
310 #[inline]
311 pub fn active_pid_ns(&self) -> Option<&PidNamespace> {
312 // SAFETY: It is safe to call `task_active_pid_ns` without RCU protection when calling it
313 // on the current task.
314 let active_ns = unsafe { bindings::task_active_pid_ns(self.as_ptr()) };
315
316 if active_ns.is_null() {
317 return None;
318 }
319
320 // The lifetime of `PidNamespace` is bound to `Task` and `struct pid`.
321 //
322 // The `PidNamespace` of a `Task` doesn't ever change once the `Task` is alive.
323 //
324 // From system call context retrieving the `PidNamespace` for the current task is always
325 // safe and requires neither RCU locking nor a reference count to be held. Retrieving the
326 // `PidNamespace` after `release_task()` for current will return `NULL` but no codepath
327 // like that is exposed to Rust.
328 //
329 // SAFETY: If `current`'s pid ns is non-null, then it references a valid pid ns.
330 // Furthermore, the returned `&PidNamespace` borrows from this `CurrentTask`, so it cannot
331 // escape the scope in which the current pointer was obtained, e.g. it cannot live past a
332 // `release_task()` call.
333 Some(unsafe { PidNamespace::from_ptr(active_ns) })
334 }
335
336 /// Returns the group leader of the current task.
337 pub fn group_leader(&self) -> &Task {
338 // SAFETY: The group leader of a task never changes while the task is running, and `self`
339 // is the current task, which is guaranteed running.
340 let ptr = unsafe { (*self.as_ptr()).group_leader };
341
342 // SAFETY: `current->group_leader` stays valid for at least the duration in which `current`
343 // is running, and the signature of this function ensures that the returned `&Task` can
344 // only be used while `current` is still valid, thus still running.
345 unsafe { &*ptr.cast() }
346 }
347}
348
349// SAFETY: The type invariants guarantee that `Task` is always refcounted.
350unsafe impl crate::sync::aref::AlwaysRefCounted for Task {
351 #[inline]
352 fn inc_ref(&self) {
353 // SAFETY: The existence of a shared reference means that the refcount is nonzero.
354 unsafe { bindings::get_task_struct(self.as_ptr()) };
355 }
356
357 #[inline]
358 unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
359 // SAFETY: The safety requirements guarantee that the refcount is nonzero.
360 unsafe { bindings::put_task_struct(obj.cast().as_ptr()) }
361 }
362}
363
364impl PartialEq for Task {
365 #[inline]
366 fn eq(&self, other: &Self) -> bool {
367 ptr::eq(self.as_ptr(), other.as_ptr())
368 }
369}
370
371impl Eq for Task {}
372
373impl Kuid {
374 /// Get the current subjective effective UID.
375 #[inline]
376 pub fn current_euid() -> Kuid {
377 // SAFETY: Just an FFI call.
378 Self::from_raw(unsafe { bindings::current_euid() })
379 }
380
381 /// Create a `Kuid` given the raw C type.
382 #[inline]
383 pub fn from_raw(kuid: bindings::kuid_t) -> Self {
384 Self { kuid }
385 }
386
387 /// Turn this kuid into the raw C type.
388 #[inline]
389 pub fn into_raw(self) -> bindings::kuid_t {
390 self.kuid
391 }
392
393 /// Converts this kernel UID into a userspace UID.
394 ///
395 /// Uses the namespace of the current task.
396 #[inline]
397 pub fn into_uid_in_current_ns(self) -> bindings::uid_t {
398 // SAFETY: Just an FFI call.
399 unsafe { bindings::from_kuid(bindings::current_user_ns(), self.kuid) }
400 }
401}
402
403impl PartialEq for Kuid {
404 #[inline]
405 fn eq(&self, other: &Kuid) -> bool {
406 // SAFETY: Just an FFI call.
407 unsafe { bindings::uid_eq(self.kuid, other.kuid) }
408 }
409}
410
411impl Eq for Kuid {}
412
413/// Annotation for functions that can sleep.
414///
415/// Equivalent to the C side [`might_sleep()`], this function serves as
416/// a debugging aid and a potential scheduling point.
417///
418/// This function can only be used in a nonatomic context.
419///
420/// [`might_sleep()`]: https://docs.kernel.org/driver-api/basics.html#c.might_sleep
421#[track_caller]
422#[inline]
423pub fn might_sleep() {
424 #[cfg(CONFIG_DEBUG_ATOMIC_SLEEP)]
425 {
426 let loc = core::panic::Location::caller();
427 let file = kernel::file_from_location(loc);
428
429 // SAFETY: `file.as_ptr()` is valid for reading and guaranteed to be nul-terminated.
430 unsafe { crate::bindings::__might_sleep(file.as_char_ptr(), loc.line() as i32) }
431 }
432
433 // SAFETY: Always safe to call.
434 unsafe { crate::bindings::might_resched() }
435}