From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 8 May 2012 21:09:46 +0000 (-0400)
Subject: rculfhash: Ensure future-proof memory barrier semantic consistency
X-Git-Tag: v0.7.0~12
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=196f4fab9bf26c48bc318ac2ff985469c4f62c7e;p=userspace-rcu.git

rculfhash: Ensure future-proof memory barrier semantic consistency

Use cmm_smp_mb__before_uatomic_or() prior to the uatomic_or() in
_rcu_lfht_del() to ensure correct memory barrier semantic when we relax
(in the future) the barrier implementation of some architectures.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/rculfhash.c b/rculfhash.c
index e9cf062..3ad3618 100644
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -1073,6 +1073,11 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
 	if (caa_unlikely(is_removed(next)))
 		return -ENOENT;
 	assert(!is_bucket(next));
+	/*
+	 * The del operation semantic guarantees a full memory barrier
+	 * before the uatomic_or atomic commit of the deletion flag.
+	 */
+	cmm_smp_mb__before_uatomic_or();
 	/*
 	 * We set the REMOVED_FLAG unconditionally. Note that there may
 	 * be more than one concurrent thread setting this flag.