From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34244) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fwsUp-00059O-GI for qemu-devel@nongnu.org; Mon, 03 Sep 2018 13:18:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fwsUm-00076o-HP for qemu-devel@nongnu.org; Mon, 03 Sep 2018 13:18:39 -0400 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:38629) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fwsUm-00075i-B9 for qemu-devel@nongnu.org; Mon, 03 Sep 2018 13:18:36 -0400 From: "Emilio G. Cota" Date: Mon, 3 Sep 2018 13:18:27 -0400 Message-Id: <20180903171831.15446-3-cota@braap.org> In-Reply-To: <20180903171831.15446-1-cota@braap.org> References: <20180903171831.15446-1-cota@braap.org> Subject: [Qemu-devel] [PATCH 2/6] test-rcu-list: avoid torn accesses to n_reclaims and n_nodes_removed List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Peter Crosthwaite , Richard Henderson , Eduardo Habkost , =?UTF-8?q?Alex=20Benn=C3=A9e?= Signed-off-by: Emilio G. Cota --- tests/test-rcu-list.c | 67 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 59 insertions(+), 8 deletions(-) diff --git a/tests/test-rcu-list.c b/tests/test-rcu-list.c index 192bfbf02e..2606b7c19d 100644 --- a/tests/test-rcu-list.c +++ b/tests/test-rcu-list.c @@ -25,6 +25,23 @@ #include "qemu/rcu.h" #include "qemu/thread.h" #include "qemu/rcu_queue.h" +#include "qemu/seqlock.h" + +/* + * Abstraction to avoid torn accesses when there is a single thread updating + * the count. + * + * If CONFIG_ATOMIC64 is defined, we simply use atomic accesses. Otherwise, we + * use a seqlock without a lock, since only one thread can update the count. + */ +struct Count { + long long val; +#ifndef CONFIG_ATOMIC64 + QemuSeqLock sequence; +#endif +}; + +typedef struct Count Count; /* * Test variables. @@ -33,8 +50,8 @@ static QemuMutex counts_mutex; static long long n_reads = 0LL; static long long n_updates = 0LL; -static long long n_reclaims = 0LL; -static long long n_nodes_removed = 0LL; +static Count n_reclaims; +static Count n_nodes_removed; static long long n_nodes = 0LL; static int g_test_in_charge = 0; @@ -60,6 +77,38 @@ static int select_random_el(int max) return (rand() % max); } +static inline long long count_read(Count *c) +{ +#ifdef CONFIG_ATOMIC64 + /* use __nocheck because sizeof(void *) might be < sizeof(long long) */ + return atomic_read__nocheck(&c->val); +#else + unsigned int version; + long long val; + + do { + version = seqlock_read_begin(&c->sequence); + val = c->val; + } while (seqlock_read_retry(&c->sequence, version)); + return val; +#endif +} + +static inline void count_add(Count *c, long long val) +{ +#ifdef CONFIG_ATOMIC64 + atomic_set__nocheck(&c->val, c->val + val); +#else + seqlock_write_begin(&c->sequence); + c->val += val; + seqlock_write_end(&c->sequence); +#endif +} + +static inline void count_inc(Count *c) +{ + count_add(c, 1); +} static void create_thread(void *(*func)(void *)) { @@ -104,7 +153,7 @@ static void reclaim_list_el(struct rcu_head *prcu) struct list_element *el = container_of(prcu, struct list_element, rcu); g_free(el); /* Accessed only from call_rcu thread. */ - n_reclaims++; + count_inc(&n_reclaims); } #if TEST_LIST_TYPE == 1 @@ -232,7 +281,7 @@ static void *rcu_q_updater(void *arg) qemu_mutex_lock(&counts_mutex); n_nodes += n_nodes_local; n_updates += n_updates_local; - n_nodes_removed += n_removed_local; + count_add(&n_nodes_removed, n_removed_local); qemu_mutex_unlock(&counts_mutex); return NULL; } @@ -286,19 +335,21 @@ static void rcu_qtest(const char *test, int duration, int nreaders) n_removed_local++; } qemu_mutex_lock(&counts_mutex); - n_nodes_removed += n_removed_local; + count_add(&n_nodes_removed, n_removed_local); qemu_mutex_unlock(&counts_mutex); synchronize_rcu(); - while (n_nodes_removed > n_reclaims) { + while (count_read(&n_nodes_removed) > count_read(&n_reclaims)) { g_usleep(100); synchronize_rcu(); } if (g_test_in_charge) { - g_assert_cmpint(n_nodes_removed, ==, n_reclaims); + g_assert_cmpint(count_read(&n_nodes_removed), ==, + count_read(&n_reclaims)); } else { printf("%s: %d readers; 1 updater; nodes read: " \ "%lld, nodes removed: %lld; nodes reclaimed: %lld\n", - test, nthreadsrunning - 1, n_reads, n_nodes_removed, n_reclaims); + test, nthreadsrunning - 1, n_reads, + count_read(&n_nodes_removed), count_read(&n_reclaims)); exit(0); } } -- 2.17.1