Messages in this thread | | | From | Wedson Almeida Filho <> | Date | Wed, 12 Apr 2023 08:42:25 -0300 | Subject | Re: [PATCH v4 09/13] rust: add basic `Task` |
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On Tue, 11 Apr 2023 at 17:47, Gary Guo <gary@garyguo.net> wrote: > > On Tue, 11 Apr 2023 02:45:39 -0300 > Wedson Almeida Filho <wedsonaf@gmail.com> wrote: > > > From: Wedson Almeida Filho <walmeida@microsoft.com> > > > > It is an abstraction for C's `struct task_struct`. It implements > > `AlwaysRefCounted`, so the refcount of the wrapped object is managed > > safely on the Rust side. > > > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> > > Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com> > > --- > > v1 -> v2: No changes > > v2 -> v3: Wrap task_struct with `Opaque` instead of `UnsafeCell` > > v3 -> v4: No changes > > > > rust/bindings/bindings_helper.h | 1 + > > rust/helpers.c | 19 +++++++++ > > rust/kernel/lib.rs | 1 + > > rust/kernel/task.rs | 75 +++++++++++++++++++++++++++++++++ > > 4 files changed, 96 insertions(+) > > create mode 100644 rust/kernel/task.rs > > > > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h > > index 75d85bd6c592..03656a44a83f 100644 > > --- a/rust/bindings/bindings_helper.h > > +++ b/rust/bindings/bindings_helper.h > > @@ -8,6 +8,7 @@ > > > > #include <linux/slab.h> > > #include <linux/refcount.h> > > +#include <linux/sched.h> > > > > /* `bindgen` gets confused at certain things. */ > > const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL; > > diff --git a/rust/helpers.c b/rust/helpers.c > > index efd5b1e86f6e..f545923aedd8 100644 > > --- a/rust/helpers.c > > +++ b/rust/helpers.c > > @@ -24,6 +24,7 @@ > > #include <linux/refcount.h> > > #include <linux/mutex.h> > > #include <linux/spinlock.h> > > +#include <linux/sched/signal.h> > > > > __noreturn void rust_helper_BUG(void) > > { > > @@ -76,6 +77,12 @@ void rust_helper_spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags) > > } > > EXPORT_SYMBOL_GPL(rust_helper_spin_unlock_irqrestore); > > > > +int rust_helper_signal_pending(struct task_struct *t) > > +{ > > + return signal_pending(t); > > +} > > +EXPORT_SYMBOL_GPL(rust_helper_signal_pending); > > + > > refcount_t rust_helper_REFCOUNT_INIT(int n) > > { > > return (refcount_t)REFCOUNT_INIT(n); > > @@ -112,6 +119,18 @@ long rust_helper_PTR_ERR(__force const void *ptr) > > } > > EXPORT_SYMBOL_GPL(rust_helper_PTR_ERR); > > > > +void rust_helper_get_task_struct(struct task_struct *t) > > +{ > > + get_task_struct(t); > > +} > > +EXPORT_SYMBOL_GPL(rust_helper_get_task_struct); > > + > > +void rust_helper_put_task_struct(struct task_struct *t) > > +{ > > + put_task_struct(t); > > +} > > +EXPORT_SYMBOL_GPL(rust_helper_put_task_struct); > > + > > /* > > * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type > > * as the Rust `usize` type, so we can use it in contexts where Rust > > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > > index 2d7606135ef6..ee27e10da479 100644 > > --- a/rust/kernel/lib.rs > > +++ b/rust/kernel/lib.rs > > @@ -44,6 +44,7 @@ mod static_assert; > > pub mod std_vendor; > > pub mod str; > > pub mod sync; > > +pub mod task; > > pub mod types; > > > > #[doc(hidden)] > > diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs > > new file mode 100644 > > index 000000000000..d70cad131956 > > --- /dev/null > > +++ b/rust/kernel/task.rs > > @@ -0,0 +1,75 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +//! Tasks (threads and processes). > > +//! > > +//! C header: [`include/linux/sched.h`](../../../../include/linux/sched.h). > > + > > +use crate::{bindings, types::Opaque}; > > +use core::ptr; > > + > > +/// Wraps the kernel's `struct task_struct`. > > +/// > > +/// # Invariants > > +/// > > +/// All instances are valid tasks created by the C portion of the kernel. > > +/// > > +/// Instances of this type are always ref-counted, that is, a call to `get_task_struct` ensures > > +/// that the allocation remains valid at least until the matching call to `put_task_struct`. > > +#[repr(transparent)] > > +pub struct Task(pub(crate) Opaque<bindings::task_struct>); > > + > > +// SAFETY: It's OK to access `Task` through references from other threads because we're either > > +// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly > > +// synchronised by C code (e.g., `signal_pending`). > > +unsafe impl Sync for Task {} > > + > > +/// The type of process identifiers (PIDs). > > +type Pid = bindings::pid_t; > > This'll just end up being `i32`. I think it'll be more desirable that > this is defined as a new type.
We may very well decide that we want to make this a new type.
But that should be done in a different patch.
> > + > > +impl Task { > > + /// Returns the group leader of the given task. > > + pub fn group_leader(&self) -> &Task { > > + // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always > > + // have a valid group_leader. > > + let ptr = unsafe { *ptr::addr_of!((*self.0.get()).group_leader) }; > > + > > + // SAFETY: The lifetime of the returned task reference is tied to the lifetime of `self`, > > + // and given that a task has a reference to its group leader, we know it must be valid for > > + // the lifetime of the returned task reference. > > + unsafe { &*ptr.cast() } > > + } > > + > > + /// Returns the PID of the given task. > > + pub fn pid(&self) -> Pid { > > + // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always > > + // have a valid pid. > > + unsafe { *ptr::addr_of!((*self.0.get()).pid) } > > + } > > + > > + /// Determines whether the given task has pending signals. > > + pub fn signal_pending(&self) -> bool { > > + // SAFETY: By the type invariant, we know that `self.0` is valid. > > + unsafe { bindings::signal_pending(self.0.get()) != 0 } > > + } > > + > > + /// Wakes up the task. > > + pub fn wake_up(&self) { > > + // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid. > > + // And `wake_up_process` is safe to be called for any valid task, even if the task is > > + // running. > > + unsafe { bindings::wake_up_process(self.0.get()) }; > > + } > > +} > > + > > +// SAFETY: The type invariants guarantee that `Task` is always ref-counted. > > +unsafe impl crate::types::AlwaysRefCounted for Task { > > + fn inc_ref(&self) { > > + // SAFETY: The existence of a shared reference means that the refcount is nonzero. > > + unsafe { bindings::get_task_struct(self.0.get()) }; > > + } > > + > > + unsafe fn dec_ref(obj: ptr::NonNull<Self>) { > > + // SAFETY: The safety requirements guarantee that the refcount is nonzero. > > + unsafe { bindings::put_task_struct(obj.cast().as_ptr()) } > > + } > > +} >
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