From 999bcff5bd185eca61a9781c043a56f06b133366 Mon Sep 17 00:00:00 2001
From: Torvald Riegel <triegel@redhat.com>
Date: Tue, 24 Jan 2012 19:17:05 +0000
Subject: [PATCH] libitm: Fix wake-up of readers in futex-based serial lock.
libitm/
* config/linux/rwlock.cc (GTM::gtm_rwlock::write_unlock): Fix reader
wake-up.
From-SVN: r183488
---
libitm/ChangeLog | 5 +++++
libitm/config/linux/rwlock.cc | 9 ++++++---
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/libitm/ChangeLog b/libitm/ChangeLog
index 4b6d156d750d..9da73d022374 100644
--- a/libitm/ChangeLog
+++ b/libitm/ChangeLog
@@ -1,3 +1,8 @@
+2012-01-24 Torvald Riegel <triegel@redhat.com>
+
+ * config/linux/rwlock.cc (GTM::gtm_rwlock::write_unlock): Fix reader
+ wake-up.
+
2012-01-24 Uros Bizjak <ubizjak@gmail.com>
* config/x86/target.h (gtm_jmpbuf) [__x86_64__]: Move rip to the
diff --git a/libitm/config/linux/rwlock.cc b/libitm/config/linux/rwlock.cc
index 24e7042ff100..ad1b042964ad 100644
--- a/libitm/config/linux/rwlock.cc
+++ b/libitm/config/linux/rwlock.cc
@@ -231,10 +231,13 @@ gtm_rwlock::write_unlock ()
// last writer (this can happen because write_lock_generic()
// exchanges 0 or 1 to 2 and thus might go to contended mode even if
// no other thread holds the write lock currently). Therefore, we
- // have to wake up readers here as well.
- futex_wake(&readers, INT_MAX);
+ // have to wake up readers here as well. Execute a barrier after
+ // the previous relaxed reset of writers (Dekker-style), and fall
+ // through to the normal reader wake-up code.
+ atomic_thread_fence (memory_order_seq_cst);
}
- return;
+ else
+ return;
}
// No waiting writers, so wake up all waiting readers.
// Because the fetch_and_sub is a full barrier already, we don't need
--
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