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