From 802748b611cbc86d29d767e5197f5a76e1803bc8 Mon Sep 17 00:00:00 2001
From: Derick Eddington <124489-kcired@users.noreply.gitlab.redox-os.org>
Date: Sat, 6 Jul 2024 01:13:23 -0700
Subject: [PATCH] Fix `Rwlock::acquire_write_lock` to avoid blocking
indefinitely.
Without this fix, `tests/bins_static/pthread/rwlock_randtest` would sometimes get stuck blocking
forever with only 1+ threads all doing `pthread_rwlock_wrlock()` but all the other threads
having finished.
---
src/sync/rwlock.rs | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/src/sync/rwlock.rs b/src/sync/rwlock.rs
index f5ecaf12..b787a8e8 100644
--- a/src/sync/rwlock.rs
+++ b/src/sync/rwlock.rs
@@ -45,7 +45,15 @@ impl Rwlock {
};
waiting_wr = expected & WAITING_WR;
- let _ = crate::sync::futex_wait(&self.state, expected, deadline);
+ if actual & COUNT_MASK > 0 {
+ let _ = crate::sync::futex_wait(&self.state, expected, deadline);
+ } else {
+ // We must avoid blocking indefinitely in our `futex_wait()`, in this case
+ // where it's possible that `self.state == expected` but our futex might
+ // never be woken again, because it's possible that all other threads
+ // already did their `futex_wake()` before we would've done our
+ // `futex_wait()`.
+ }
}
}
}
--
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