From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47556) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFmSO-0003tQ-Cb for qemu-devel@nongnu.org; Thu, 16 Jul 2015 12:56:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFmSL-0008P8-G3 for qemu-devel@nongnu.org; Thu, 16 Jul 2015 12:56:24 -0400 Received: from mail-wi0-x233.google.com ([2a00:1450:400c:c05::233]:34024) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFmSL-0008Ox-9L for qemu-devel@nongnu.org; Thu, 16 Jul 2015 12:56:21 -0400 Received: by wibud3 with SMTP id ud3so20345582wib.1 for ; Thu, 16 Jul 2015 09:56:20 -0700 (PDT) Received: from donizetti.localdomain (host231-210-dynamic.21-79-r.retail.telecomitalia.it. [79.21.210.231]) by smtp.gmail.com with ESMTPSA id lq9sm14006305wjb.35.2015.07.16.09.56.19 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 Jul 2015 09:56:19 -0700 (PDT) Sender: Paolo Bonzini From: Paolo Bonzini Date: Thu, 16 Jul 2015 18:55:55 +0200 Message-Id: <1437065758-4625-9-git-send-email-pbonzini@redhat.com> In-Reply-To: <1437065758-4625-1-git-send-email-pbonzini@redhat.com> References: <1437065758-4625-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PULL 08/11] rcu: detect missing rcu_register_thread() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Use an "impossible" value for the .depth field in order to quickly detect threads that have not registered themselves with the RCU subsystem. Avoid a false positive around forking by unregistering and registering the forking thread explicitly. Previously, it was enough to re-register the thread. Signed-off-by: Paolo Bonzini --- include/qemu/rcu.h | 4 +++- util/rcu.c | 35 ++++++++++++++++++++++++++++++----- 2 files changed, 33 insertions(+), 6 deletions(-) diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h index 7df1e86..4facb35 100644 --- a/include/qemu/rcu.h +++ b/include/qemu/rcu.h @@ -82,7 +82,9 @@ static inline void rcu_read_lock(void) struct rcu_reader_data *p_rcu_reader = &rcu_reader; unsigned ctr; - if (p_rcu_reader->depth++ > 0) { + p_rcu_reader->depth++; + assert(p_rcu_reader->depth >= 1); + if (p_rcu_reader->depth > 1) { return; } diff --git a/util/rcu.c b/util/rcu.c index e21bb46..2490273 100644 --- a/util/rcu.c +++ b/util/rcu.c @@ -63,8 +63,11 @@ static inline int rcu_gp_ongoing(unsigned long *ctr) /* Written to only by each individual reader. Read by both the reader and the * writers. + * + * Initializing the depth to -1 causes an assertion failure on the first + * call to rcu_read_lock() if the thread does not call rcu_register_thread(). */ -__thread struct rcu_reader_data rcu_reader; +__thread struct rcu_reader_data rcu_reader = { .depth = -1 }; /* Protected by rcu_gp_lock. */ typedef QLIST_HEAD(, rcu_reader_data) ThreadList; @@ -279,7 +282,12 @@ static void rcu_unregister_thread_notify(Notifier *n, void *data) void rcu_register_thread(void) { - assert(rcu_reader.ctr == 0); + /* rcu_reader.depth is also used to detect whether the thread is + * registered. + */ + assert(rcu_reader.depth == -1); + rcu_reader.depth = 0; + qemu_mutex_lock(&rcu_gp_lock); QLIST_INSERT_HEAD(®istry, &rcu_reader, node); qemu_mutex_unlock(&rcu_gp_lock); @@ -290,6 +298,12 @@ void rcu_register_thread(void) void rcu_unregister_thread(void) { + /* Resetting the depth to -1 causes an assertion failure on the next + * call to rcu_read_lock(). + */ + assert(rcu_reader.depth == 0); + rcu_reader.depth = -1; + qemu_mutex_lock(&rcu_gp_lock); QLIST_REMOVE(&rcu_reader, node); qemu_mutex_unlock(&rcu_gp_lock); @@ -301,7 +315,6 @@ static void rcu_init_complete(void) { QemuThread thread; - qemu_mutex_init(&rcu_gp_lock); qemu_event_init(&rcu_gp_event, true); qemu_event_init(&rcu_call_ready_event, false); @@ -311,8 +324,6 @@ static void rcu_init_complete(void) */ qemu_thread_create(&thread, "call_rcu", call_rcu_thread, NULL, QEMU_THREAD_DETACHED); - - rcu_register_thread(); } #ifdef CONFIG_POSIX @@ -329,14 +340,28 @@ static void rcu_init_unlock(void) void rcu_after_fork(void) { + int save_depth = rcu_reader.depth; + if (save_depth != -1) { + rcu_unregister_thread(); + } + memset(®istry, 0, sizeof(registry)); + rcu_init_complete(); + + if (save_depth != -1) { + rcu_register_thread(); + rcu_reader.depth = save_depth; + } } static void __attribute__((__constructor__)) rcu_init(void) { + qemu_mutex_init(&rcu_gp_lock); #ifdef CONFIG_POSIX pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_unlock); #endif rcu_init_complete(); + + rcu_register_thread(); } -- 2.4.3