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Unix RwLock: avoid racy access to write_locked #55865

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Merged
merged 2 commits into from
Nov 15, 2018
Merged

Unix RwLock: avoid racy access to write_locked #55865

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0c6a093
Unix RwLock: avoid racy access to write_locked
RalfJung Nov 11, 2018
db13390
do not skip return code check in release builds
RalfJung Nov 11, 2018
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6 changes: 3 additions & 3 deletions src/libstd/sys/unix/rwlock.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ use sync::atomic::{AtomicUsize, Ordering};

pub struct RWLock {
inner: UnsafeCell<libc::pthread_rwlock_t>,
write_locked: UnsafeCell<bool>,
write_locked: UnsafeCell<bool>, // guarded by the `inner` RwLock
num_readers: AtomicUsize,
}

Expand Down Expand Up @@ -52,13 +52,13 @@ impl RWLock {
// allow that because it could lead to aliasing issues.
if r == libc::EAGAIN {
panic!("rwlock maximum reader count exceeded");
} else if r == libc::EDEADLK || *self.write_locked.get() {
} else if r == libc::EDEADLK || (r == 0 && *self.write_locked.get()) {
if r == 0 {
self.raw_unlock();
}
panic!("rwlock read lock would result in deadlock");
} else {
debug_assert_eq!(r, 0);
assert_eq!(r, 0);
self.num_readers.fetch_add(1, Ordering::Relaxed);
}
}
Expand Down