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Refine comments about the lock usage

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This commit is contained in:
Ruihan Li
2024-11-18 21:07:58 +08:00
committed by Tate, Hongliang Tian
parent 85e1f0973b
commit b3f8d21c3d
1 changed files with 9 additions and 10 deletions
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19
kernel/src/fs/epoll/entry.rs
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@ -105,7 +105,8 @@ impl Entry {
let file = self.file()?; let file = self.file()?;
let inner = self.inner.lock(); let inner = self.inner.lock();
// There are no events if the entry is disabled. // There are no events if the entry is disabled. Note that this check should be done after
// locking `Inner` to avoid race conditions.
if !self.observer.is_enabled() { if !self.observer.is_enabled() {
return Some((None, false)); return Some((None, false));
} }
@ -207,10 +208,9 @@ impl Observer {
/// Returns whether the epoll entry is in the ready list. /// Returns whether the epoll entry is in the ready list.
/// ///
/// *Caution:* If this method is called without holding the lock of the ready list, the user /// This method needs to be called while holding the lock of the ready list. See also
/// must ensure that the behavior is desired with respect to the way the ready list might be /// [`Self::set_ready`] and [`Self::reset_ready`].
/// modified concurrently. fn is_ready(&self, _guard: &SpinLockGuard<VecDeque<Weak<Entry>>, LocalIrqDisabled>) -> bool {
fn is_ready(&self) -> bool {
self.is_ready.load(Ordering::Relaxed) self.is_ready.load(Ordering::Relaxed)
} }
@ -293,13 +293,12 @@ impl ReadySet {
} }
pub(super) fn push(&self, observer: &Observer) { pub(super) fn push(&self, observer: &Observer) {
// Note that we cannot take the `Inner` lock because we are in the callback of the event // Note that we cannot take the `Inner` lock because we may be in the callback of the event
// observer. Doing so will cause dead locks due to inconsistent locking orders. // observer. Doing so will cause dead locks due to inconsistent locking orders.
// //
// We don't need to take the lock because // We don't need to take the lock because
// - We always call `file.poll()` immediately after calling `self.set_enabled()` and // - `set_enabled` is guaranteed to be visible after its following `FileLike::poll`. This
// `file.register_observer()`, so all events are caught either here or by the immediate // synchronization relies on the lock in `Subject`. As a result, no events are lost.
// poll; in other words, we don't lose any events.
// - Catching spurious events here is always fine because we always check them later before // - Catching spurious events here is always fine because we always check them later before
// returning events to the user (in `Entry::poll`). // returning events to the user (in `Entry::poll`).
if !observer.is_enabled() { if !observer.is_enabled() {
@ -308,7 +307,7 @@ impl ReadySet {
let mut entries = self.entries.lock(); let mut entries = self.entries.lock();
if !observer.is_ready() { if !observer.is_ready(&entries) {
observer.set_ready(&entries); observer.set_ready(&entries);
entries.push_back(observer.weak_entry().clone()) entries.push_back(observer.weak_entry().clone())
} }