1 files changed, 54 insertions, 27 deletions

diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index 0f79a2ec9474..d0e6c6e162c2 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -12,26 +12,28 @@ use crate::{
     error::{Error, Result},
     ffi::c_void,
     prelude::*,
-    revocable::Revocable,
-    sync::Arc,
+    revocable::{Revocable, RevocableGuard},
+    sync::{rcu, Arc, Completion},
     types::ARef,
 };
 
-use core::ops::Deref;
-
 #[pin_data]
 struct DevresInner<T> {
     dev: ARef<Device>,
     callback: unsafe extern "C" fn(*mut c_void),
     #[pin]
     data: Revocable<T>,
+    #[pin]
+    revoke: Completion,
 }
 
 /// This abstraction is meant to be used by subsystems to containerize [`Device`] bound resources to
 /// manage their lifetime.
 ///
 /// [`Device`] bound resources should be freed when either the resource goes out of scope or the
-/// [`Device`] is unbound respectively, depending on what happens first.
+/// [`Device`] is unbound respectively, depending on what happens first. In any case, it is always
+/// guaranteed that revoking the device resource is completed before the corresponding [`Device`]
+/// is unbound.
 ///
 /// To achieve that [`Devres`] registers a devres callback on creation, which is called once the
 /// [`Device`] is unbound, revoking access to the encapsulated resource (see also [`Revocable`]).
@@ -42,7 +44,7 @@ struct DevresInner<T> {
 /// [`Devres`] users should make sure to simply free the corresponding backing resource in `T`'s
 /// [`Drop`] implementation.
 ///
-/// # Example
+/// # Examples
 ///
 /// ```no_run
 /// # use kernel::{bindings, c_str, device::{Bound, Device}, devres::Devres, io::{Io, IoRaw}};
@@ -59,19 +61,19 @@ struct DevresInner<T> {
 ///     unsafe fn new(paddr: usize) -> Result<Self>{
 ///         // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
 ///         // valid for `ioremap`.
-///         let addr = unsafe { bindings::ioremap(paddr as _, SIZE as _) };
+///         let addr = unsafe { bindings::ioremap(paddr as bindings::phys_addr_t, SIZE) };
 ///         if addr.is_null() {
 ///             return Err(ENOMEM);
 ///         }
 ///
-///         Ok(IoMem(IoRaw::new(addr as _, SIZE)?))
+///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
 ///     }
 /// }
 ///
 /// impl<const SIZE: usize> Drop for IoMem<SIZE> {
 ///     fn drop(&mut self) {
 ///         // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
-///         unsafe { bindings::iounmap(self.0.addr() as _); };
+///         unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
 ///     }
 /// }
 ///
@@ -102,6 +104,7 @@ impl<T> DevresInner<T> {
                 dev: dev.into(),
                 callback: Self::devres_callback,
                 data <- Revocable::new(data),
+                revoke <- Completion::new(),
             }),
             flags,
         )?;
@@ -112,8 +115,9 @@ impl<T> DevresInner<T> {
 
         // SAFETY: `devm_add_action` guarantees to call `Self::devres_callback` once `dev` is
         // detached.
-        let ret =
-            unsafe { bindings::devm_add_action(dev.as_raw(), Some(inner.callback), data as _) };
+        let ret = unsafe {
+            bindings::devm_add_action(dev.as_raw(), Some(inner.callback), data.cast_mut().cast())
+        };
 
         if ret != 0 {
             // SAFETY: We just created another reference to `inner` in order to pass it to
@@ -127,41 +131,48 @@ impl<T> DevresInner<T> {
     }
 
     fn as_ptr(&self) -> *const Self {
-        self as _
+        self
     }
 
-    fn remove_action(this: &Arc<Self>) {
+    fn remove_action(this: &Arc<Self>) -> bool {
         // SAFETY:
         // - `self.inner.dev` is a valid `Device`,
         // - the `action` and `data` pointers are the exact same ones as given to devm_add_action()
         //   previously,
         // - `self` is always valid, even if the action has been released already.
-        let ret = unsafe {
+        let success = unsafe {
             bindings::devm_remove_action_nowarn(
                 this.dev.as_raw(),
                 Some(this.callback),
-                this.as_ptr() as _,
+                this.as_ptr().cast_mut().cast(),
             )
-        };
+        } == 0;
 
-        if ret == 0 {
+        if success {
             // SAFETY: We leaked an `Arc` reference to devm_add_action() in `DevresInner::new`; if
             // devm_remove_action_nowarn() was successful we can (and have to) claim back ownership
             // of this reference.
             let _ = unsafe { Arc::from_raw(this.as_ptr()) };
         }
+
+        success
     }
 
     #[allow(clippy::missing_safety_doc)]
     unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) {
-        let ptr = ptr as *mut DevresInner<T>;
+        let ptr = ptr.cast::<DevresInner<T>>();
         // Devres owned this memory; now that we received the callback, drop the `Arc` and hence the
         // reference.
         // SAFETY: Safe, since we leaked an `Arc` reference to devm_add_action() in
         //         `DevresInner::new`.
         let inner = unsafe { Arc::from_raw(ptr) };
 
-        inner.data.revoke();
+        if !inner.data.revoke() {
+            // If `revoke()` returns false, it means that `Devres::drop` already started revoking
+            // `inner.data` for us. Hence we have to wait until `Devres::drop()` signals that it
+            // completed revoking `inner.data`.
+            inner.revoke.wait_for_completion();
+        }
     }
 }
 
@@ -192,7 +203,7 @@ impl<T> Devres<T> {
     /// An error is returned if `dev` does not match the same [`Device`] this [`Devres`] instance
     /// has been created with.
     ///
-    /// # Example
+    /// # Examples
     ///
     /// ```no_run
     /// # #![cfg(CONFIG_PCI)]
@@ -218,20 +229,36 @@ impl<T> Devres<T> {
         // SAFETY: `dev` being the same device as the device this `Devres` has been created for
         // proves that `self.0.data` hasn't been revoked and is guaranteed to not be revoked as
         // long as `dev` lives; `dev` lives at least as long as `self`.
-        Ok(unsafe { self.deref().access() })
+        Ok(unsafe { self.0.data.access() })
+    }
+
+    /// [`Devres`] accessor for [`Revocable::try_access`].
+    pub fn try_access(&self) -> Option<RevocableGuard<'_, T>> {
+        self.0.data.try_access()
     }
-}
 
-impl<T> Deref for Devres<T> {
-    type Target = Revocable<T>;
+    /// [`Devres`] accessor for [`Revocable::try_access_with`].
+    pub fn try_access_with<R, F: FnOnce(&T) -> R>(&self, f: F) -> Option<R> {
+        self.0.data.try_access_with(f)
+    }
 
-    fn deref(&self) -> &Self::Target {
-        &self.0.data
+    /// [`Devres`] accessor for [`Revocable::try_access_with_guard`].
+    pub fn try_access_with_guard<'a>(&'a self, guard: &'a rcu::Guard) -> Option<&'a T> {
+        self.0.data.try_access_with_guard(guard)
     }
 }
 
 impl<T> Drop for Devres<T> {
     fn drop(&mut self) {
-        DevresInner::remove_action(&self.0);
+        // SAFETY: When `drop` runs, it is guaranteed that nobody is accessing the revocable data
+        // anymore, hence it is safe not to wait for the grace period to finish.
+        if unsafe { self.0.data.revoke_nosync() } {
+            // We revoked `self.0.data` before the devres action did, hence try to remove it.
+            if !DevresInner::remove_action(&self.0) {
+                // We could not remove the devres action, which means that it now runs concurrently,
+                // hence signal that `self.0.data` has been revoked successfully.
+                self.0.revoke.complete_all();
+            }
+        }
     }
 }