From: Alice Ryhl Date: Mon, 23 Jun 2025 13:57:27 +0000 (+0000) Subject: poll: rust: allow poll_table ptrs to be null X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=de747bd023c09b5b7f3bf5c952d7b1da77a9caaa;p=thirdparty%2Fkernel%2Flinux.git poll: rust: allow poll_table ptrs to be null It's possible for a poll_table to be null. This can happen if an end-user just wants to know if a resource has events right now without registering a waiter for when events become available. Furthermore, these null pointers should be handled transparently by the API, so we should not change `from_ptr` to return an `Option`. Thus, change `PollTable` to wrap a raw pointer rather than use a reference so that you can pass null. Comments mentioning `struct poll_table` are changed to just `poll_table` since `poll_table` is a typedef. (It's a typedef because it's supposed to be opaque.) Reviewed-by: Benno Lossin Signed-off-by: Alice Ryhl --- diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c index 0f1b5d1159859..ff65073fe3a52 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -30,6 +30,7 @@ #include "platform.c" #include "pci.c" #include "pid_namespace.c" +#include "poll.c" #include "rbtree.c" #include "rcu.c" #include "refcount.c" diff --git a/rust/helpers/poll.c b/rust/helpers/poll.c new file mode 100644 index 0000000000000..7e5b1751c2d52 --- /dev/null +++ b/rust/helpers/poll.c @@ -0,0 +1,10 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include + +void rust_helper_poll_wait(struct file *filp, wait_queue_head_t *wait_address, + poll_table *p) +{ + poll_wait(filp, wait_address, p); +} diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs index d7e6e59e124b0..69f1368a2151c 100644 --- a/rust/kernel/sync/poll.rs +++ b/rust/kernel/sync/poll.rs @@ -9,9 +9,8 @@ use crate::{ fs::File, prelude::*, sync::{CondVar, LockClassKey}, - types::Opaque, }; -use core::ops::Deref; +use core::{marker::PhantomData, ops::Deref}; /// Creates a [`PollCondVar`] initialiser with the given name and a newly-created lock class. #[macro_export] @@ -23,58 +22,43 @@ macro_rules! new_poll_condvar { }; } -/// Wraps the kernel's `struct poll_table`. +/// Wraps the kernel's `poll_table`. /// /// # Invariants /// -/// This struct contains a valid `struct poll_table`. -/// -/// For a `struct poll_table` to be valid, its `_qproc` function must follow the safety -/// requirements of `_qproc` functions: -/// -/// * The `_qproc` function is given permission to enqueue a waiter to the provided `poll_table` -/// during the call. Once the waiter is removed and an rcu grace period has passed, it must no -/// longer access the `wait_queue_head`. +/// The pointer must be null or reference a valid `poll_table`. #[repr(transparent)] -pub struct PollTable(Opaque); +pub struct PollTable<'a> { + table: *mut bindings::poll_table, + _lifetime: PhantomData<&'a bindings::poll_table>, +} -impl PollTable { - /// Creates a reference to a [`PollTable`] from a valid pointer. +impl<'a> PollTable<'a> { + /// Creates a [`PollTable`] from a valid pointer. /// /// # Safety /// - /// The caller must ensure that for the duration of `'a`, the pointer will point at a valid poll - /// table (as defined in the type invariants). - /// - /// The caller must also ensure that the `poll_table` is only accessed via the returned - /// reference for the duration of `'a`. - pub unsafe fn from_ptr<'a>(ptr: *mut bindings::poll_table) -> &'a mut PollTable { - // SAFETY: The safety requirements guarantee the validity of the dereference, while the - // `PollTable` type being transparent makes the cast ok. - unsafe { &mut *ptr.cast() } - } - - fn get_qproc(&self) -> bindings::poll_queue_proc { - let ptr = self.0.get(); - // SAFETY: The `ptr` is valid because it originates from a reference, and the `_qproc` - // field is not modified concurrently with this call since we have an immutable reference. - unsafe { (*ptr)._qproc } + /// The pointer must be null or reference a valid `poll_table` for the duration of `'a`. + pub unsafe fn from_raw(table: *mut bindings::poll_table) -> Self { + // INVARIANTS: The safety requirements are the same as the struct invariants. + PollTable { + table, + _lifetime: PhantomData, + } } /// Register this [`PollTable`] with the provided [`PollCondVar`], so that it can be notified /// using the condition variable. - pub fn register_wait(&mut self, file: &File, cv: &PollCondVar) { - if let Some(qproc) = self.get_qproc() { - // SAFETY: The pointers to `file` and `self` need to be valid for the duration of this - // call to `qproc`, which they are because they are references. - // - // The `cv.wait_queue_head` pointer must be valid until an rcu grace period after the - // waiter is removed. The `PollCondVar` is pinned, so before `cv.wait_queue_head` can - // be destroyed, the destructor must run. That destructor first removes all waiters, - // and then waits for an rcu grace period. Therefore, `cv.wait_queue_head` is valid for - // long enough. - unsafe { qproc(file.as_ptr() as _, cv.wait_queue_head.get(), self.0.get()) }; - } + pub fn register_wait(&self, file: &File, cv: &PollCondVar) { + // SAFETY: + // * `file.as_ptr()` references a valid file for the duration of this call. + // * `self.table` is null or references a valid poll_table for the duration of this call. + // * Since `PollCondVar` is pinned, its destructor is guaranteed to run before the memory + // containing `cv.wait_queue_head` is invalidated. Since the destructor clears all + // waiters and then waits for an rcu grace period, it's guaranteed that + // `cv.wait_queue_head` remains valid for at least an rcu grace period after the removal + // of the last waiter. + unsafe { bindings::poll_wait(file.as_ptr(), cv.wait_queue_head.get(), self.table) } } }