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Auto merge of #13472 - asajeffrey:util-remutex-dont-log-while-mutating-lock, r=jdm
Don't log in the middle of mutating a reentrant lock <!-- Please describe your changes on the following line: --> Moved assertion that we are the lock owner to after the lock release. The problem is that Servo uses a reentrant lock for logging, so logging in the middle of mutating the lock is A Bad Idea. While I was at it, I tidied up the reentrant lock code. cc @jdm --- <!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: --> - [X] `./mach build -d` does not report any errors - [X] `./mach test-tidy` does not report any errors - [X] These changes fix #13463. - [X] These changes do not require tests because they fix an existing intermittent. <!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. --> <!-- Reviewable:start --> --- This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/13472) <!-- Reviewable:end -->
This commit is contained in:
commit
318b23ed00
2 changed files with 27 additions and 9 deletions
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@ -12,7 +12,6 @@
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use core::nonzero::NonZero;
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use std::cell::{Cell, UnsafeCell};
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use std::mem;
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use std::ops::Deref;
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use std::sync::{LockResult, Mutex, MutexGuard, PoisonError, TryLockError, TryLockResult};
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use std::sync::atomic::{AtomicUsize, Ordering};
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@ -87,13 +86,34 @@ impl HandOverHandMutex {
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}
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}
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#[allow(unsafe_code)]
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pub fn lock(&self) -> LockResult<()> {
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unsafe fn set_guard_and_owner<'a>(&'a self, guard: MutexGuard<'a, ()>) {
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// The following two lines allow us to unsafely store
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// Some(guard): Option<MutexGuard<'a, ()>
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// in self.guard, even though its contents are Option<MutexGuard<'static, ()>>,
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// that is the lifetime is 'a not 'static.
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let guard_ptr = &mut *(self.guard.get() as *mut u8 as *mut Option<MutexGuard<'a, ()>>);
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*guard_ptr = Some(guard);
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self.owner.store(Some(ThreadId::current()), Ordering::Relaxed);
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}
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#[allow(unsafe_code)]
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unsafe fn unset_guard_and_owner(&self) {
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let guard_ptr = &mut *self.guard.get();
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let old_owner = self.owner();
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self.owner.store(None, Ordering::Relaxed);
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// Make sure we release the lock before checking the assertions.
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// We protect logging by a re-entrant lock, so we don't want
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// to do any incidental logging while we the lock is held.
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drop(guard_ptr.take());
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// Now we have released the lock, it's okay to use logging.
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assert_eq!(old_owner, Some(ThreadId::current()));
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}
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#[allow(unsafe_code)]
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pub fn lock<'a>(&'a self) -> LockResult<()> {
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let (guard, result) = match self.mutex.lock() {
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Ok(guard) => (guard, Ok(())),
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Err(err) => (err.into_inner(), Err(PoisonError::new(()))),
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};
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unsafe { *self.guard.get().as_mut().unwrap() = mem::transmute(guard) };
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self.owner.store(Some(ThreadId::current()), Ordering::Relaxed);
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unsafe { self.set_guard_and_owner(guard); }
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result
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}
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#[allow(unsafe_code)]
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@ -103,15 +123,12 @@ impl HandOverHandMutex {
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Err(TryLockError::WouldBlock) => return Err(TryLockError::WouldBlock),
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Err(TryLockError::Poisoned(err)) => (err.into_inner(), Err(TryLockError::Poisoned(PoisonError::new(())))),
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};
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unsafe { *self.guard.get().as_mut().unwrap() = mem::transmute(guard) };
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self.owner.store(Some(ThreadId::current()), Ordering::Relaxed);
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unsafe { self.set_guard_and_owner(guard); }
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result
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}
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#[allow(unsafe_code)]
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pub fn unlock(&self) {
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assert_eq!(Some(ThreadId::current()), self.owner.load(Ordering::Relaxed));
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self.owner.store(None, Ordering::Relaxed);
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unsafe { *self.guard.get().as_mut().unwrap() = None; }
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unsafe { self.unset_guard_and_owner(); }
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}
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pub fn owner(&self) -> Option<ThreadId> {
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self.owner.load(Ordering::Relaxed)
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@ -1,3 +1,4 @@
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/css-flexbox-1_dev/html/flexbox-basic-iframe-vert-001.htm
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/css-transforms-1_dev/html/transform-table-007.htm
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/css-transforms-1_dev/html/transform-abspos-002.htm
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/css-transforms-1_dev/html/transform-abspos-007.htm
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