From patchwork Fri Mar 13 13:06:11 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: =?utf-8?b?SsO8cmdlbiBHcm/Dnw==?= X-Patchwork-Id: 11436869 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D8D96921 for ; Fri, 13 Mar 2020 13:07:37 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BFD4A2073E for ; Fri, 13 Mar 2020 13:07:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BFD4A2073E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jCk1H-0001AU-5R; Fri, 13 Mar 2020 13:06:31 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jCk1F-00019v-5A for xen-devel@lists.xenproject.org; Fri, 13 Mar 2020 13:06:29 +0000 X-Inumbo-ID: 6cd2afef-652b-11ea-b2f0-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 6cd2afef-652b-11ea-b2f0-12813bfff9fa; Fri, 13 Mar 2020 13:06:17 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id CA996AFBA; Fri, 13 Mar 2020 13:06:16 +0000 (UTC) From: Juergen Gross To: xen-devel@lists.xenproject.org Date: Fri, 13 Mar 2020 14:06:11 +0100 Message-Id: <20200313130614.27265-2-jgross@suse.com> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20200313130614.27265-1-jgross@suse.com> References: <20200313130614.27265-1-jgross@suse.com> Subject: [Xen-devel] [PATCH v6 1/4] xen/rcu: don't use stop_machine_run() for rcu_barrier() X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Stefano Stabellini , Julien Grall , Wei Liu , Andrew Cooper , Ian Jackson , George Dunlap , Jan Beulich MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Today rcu_barrier() is calling stop_machine_run() to synchronize all physical cpus in order to ensure all pending rcu calls have finished when returning. As stop_machine_run() is using tasklets this requires scheduling of idle vcpus on all cpus imposing the need to call rcu_barrier() on idle cpus only in case of core scheduling being active, as otherwise a scheduling deadlock would occur. There is no need at all to do the syncing of the cpus in tasklets, as rcu activity is started in __do_softirq() called whenever softirq activity is allowed. So rcu_barrier() can easily be modified to use softirq for synchronization of the cpus no longer requiring any scheduling activity. As there already is a rcu softirq reuse that for the synchronization. Remove the barrier element from struct rcu_data as it isn't used. Finally switch rcu_barrier() to return void as it now can never fail. Partially-based-on-patch-by: Igor Druzhinin Signed-off-by: Juergen Gross --- V2: - add recursion detection V3: - fix races (Igor Druzhinin) V5: - rename done_count to pending_count (Jan Beulich) - fix race (Jan Beulich) V6: - add barrier (Julien Grall) - add ASSERT() (Julien Grall) - hold cpu_map lock until end of rcu_barrier() (Julien Grall) --- xen/common/rcupdate.c | 95 +++++++++++++++++++++++++++++++++------------- xen/include/xen/rcupdate.h | 2 +- 2 files changed, 69 insertions(+), 28 deletions(-) diff --git a/xen/common/rcupdate.c b/xen/common/rcupdate.c index 03d84764d2..ed9083d2b2 100644 --- a/xen/common/rcupdate.c +++ b/xen/common/rcupdate.c @@ -83,7 +83,6 @@ struct rcu_data { struct rcu_head **donetail; long blimit; /* Upper limit on a processed batch */ int cpu; - struct rcu_head barrier; long last_rs_qlen; /* qlen during the last resched */ /* 3) idle CPUs handling */ @@ -91,6 +90,7 @@ struct rcu_data { bool idle_timer_active; bool process_callbacks; + bool barrier_active; }; /* @@ -143,51 +143,85 @@ static int qhimark = 10000; static int qlowmark = 100; static int rsinterval = 1000; -struct rcu_barrier_data { - struct rcu_head head; - atomic_t *cpu_count; -}; +/* + * rcu_barrier() handling: + * cpu_count holds the number of cpus required to finish barrier handling. + * pending_count is initialized to nr_cpus + 1. + * Cpus are synchronized via softirq mechanism. rcu_barrier() is regarded to + * be active if pending_count is not zero. In case rcu_barrier() is called on + * multiple cpus it is enough to check for pending_count being not zero on entry + * and to call process_pending_softirqs() in a loop until pending_count drops to + * zero, before starting the new rcu_barrier() processing. + * In order to avoid hangs when rcu_barrier() is called multiple times on the + * same cpu in fast sequence and a slave cpu couldn't drop out of the + * barrier handling fast enough a second counter pending_count is needed. + * The rcu_barrier() invoking cpu will wait until pending_count reaches 1 + * (meaning that all cpus have finished processing the barrier) and then will + * reset pending_count to 0 to enable entering rcu_barrier() again. + */ +static atomic_t cpu_count = ATOMIC_INIT(0); +static atomic_t pending_count = ATOMIC_INIT(0); static void rcu_barrier_callback(struct rcu_head *head) { - struct rcu_barrier_data *data = container_of( - head, struct rcu_barrier_data, head); - atomic_inc(data->cpu_count); + smp_wmb(); /* Make all previous writes visible to other cpus. */ + atomic_dec(&cpu_count); } -static int rcu_barrier_action(void *_cpu_count) +static void rcu_barrier_action(void) { - struct rcu_barrier_data data = { .cpu_count = _cpu_count }; - - ASSERT(!local_irq_is_enabled()); - local_irq_enable(); + struct rcu_head head; /* * When callback is executed, all previously-queued RCU work on this CPU - * is completed. When all CPUs have executed their callback, data.cpu_count - * will have been incremented to include every online CPU. + * is completed. When all CPUs have executed their callback, cpu_count + * will have been decremented to 0. */ - call_rcu(&data.head, rcu_barrier_callback); + call_rcu(&head, rcu_barrier_callback); - while ( atomic_read(data.cpu_count) != num_online_cpus() ) + while ( atomic_read(&cpu_count) ) { process_pending_softirqs(); cpu_relax(); } - local_irq_disable(); - - return 0; + atomic_dec(&pending_count); } -/* - * As rcu_barrier() is using stop_machine_run() it is allowed to be used in - * idle context only (see comment for stop_machine_run()). - */ -int rcu_barrier(void) +void rcu_barrier(void) { - atomic_t cpu_count = ATOMIC_INIT(0); - return stop_machine_run(rcu_barrier_action, &cpu_count, NR_CPUS); + unsigned int n_cpus; + + ASSERT(!in_irq() && local_irq_is_enabled()); + + for ( ;; ) + { + if ( !atomic_read(&pending_count) && get_cpu_maps() ) + { + n_cpus = num_online_cpus(); + + if ( atomic_cmpxchg(&pending_count, 0, n_cpus + 1) == 0 ) + break; + + put_cpu_maps(); + } + + process_pending_softirqs(); + cpu_relax(); + } + + atomic_set(&cpu_count, n_cpus); + cpumask_raise_softirq(&cpu_online_map, RCU_SOFTIRQ); + + while ( atomic_read(&pending_count) != 1 ) + { + process_pending_softirqs(); + cpu_relax(); + } + + atomic_set(&pending_count, 0); + + put_cpu_maps(); } /* Is batch a before batch b ? */ @@ -426,6 +460,13 @@ static void rcu_process_callbacks(void) rdp->process_callbacks = false; __rcu_process_callbacks(&rcu_ctrlblk, rdp); } + + if ( atomic_read(&cpu_count) && !rdp->barrier_active ) + { + rdp->barrier_active = true; + rcu_barrier_action(); + rdp->barrier_active = false; + } } static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp) diff --git a/xen/include/xen/rcupdate.h b/xen/include/xen/rcupdate.h index eb9b60df07..31c8b86d13 100644 --- a/xen/include/xen/rcupdate.h +++ b/xen/include/xen/rcupdate.h @@ -144,7 +144,7 @@ void rcu_check_callbacks(int cpu); void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *head)); -int rcu_barrier(void); +void rcu_barrier(void); void rcu_idle_enter(unsigned int cpu); void rcu_idle_exit(unsigned int cpu); From patchwork Fri Mar 13 13:06:13 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?b?SsO8cmdlbiBHcm/Dnw==?= X-Patchwork-Id: 11436875 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id F2306921 for ; Fri, 13 Mar 2020 13:07:49 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D91DA20724 for ; Fri, 13 Mar 2020 13:07:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D91DA20724 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jCk1A-000192-Kp; Fri, 13 Mar 2020 13:06:24 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jCk19-00018p-AB for xen-devel@lists.xenproject.org; Fri, 13 Mar 2020 13:06:23 +0000 X-Inumbo-ID: 6cfd6608-652b-11ea-bec1-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 6cfd6608-652b-11ea-bec1-bc764e2007e4; Fri, 13 Mar 2020 13:06:18 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 36397B001; Fri, 13 Mar 2020 13:06:17 +0000 (UTC) From: Juergen Gross To: xen-devel@lists.xenproject.org Date: Fri, 13 Mar 2020 14:06:13 +0100 Message-Id: <20200313130614.27265-4-jgross@suse.com> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20200313130614.27265-1-jgross@suse.com> References: <20200313130614.27265-1-jgross@suse.com> MIME-Version: 1.0 Subject: [Xen-devel] [PATCH v6 3/4] xen/rcu: add assertions to debug build X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Stefano Stabellini , Julien Grall , Wei Liu , Andrew Cooper , Ian Jackson , George Dunlap , Jan Beulich Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Xen's RCU implementation relies on no softirq handling taking place while being in a RCU critical section. Add ASSERT()s in debug builds in order to catch any violations. For that purpose modify rcu_read_[un]lock() to use a dedicated percpu counter additional to preempt_[en|dis]able() as this enables to test that condition in __do_softirq() (ASSERT_NOT_IN_ATOMIC() is not usable there due to __cpu_up() calling process_pending_softirqs() while holding the cpu hotplug lock). While at it switch the rcu_read_[un]lock() implementation to static inline functions instead of macros. Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich --- V3: - add barriers to rcu_[en|dis]able() (Roger Pau Monné) - add rcu_quiesce_allowed() to ASSERT_NOT_IN_ATOMIC (Roger Pau Monné) - convert macros to static inline functions - add sanity check in rcu_read_unlock() V4: - use barrier() in rcu_[en|dis]able() (Julien Grall) V5: - use rcu counter even if not using a debug build V6: - keep preempt_[dis|en]able() calls --- xen/common/rcupdate.c | 2 ++ xen/common/softirq.c | 4 +++- xen/include/xen/rcupdate.h | 36 +++++++++++++++++++++++++++++++++--- 3 files changed, 38 insertions(+), 4 deletions(-) diff --git a/xen/common/rcupdate.c b/xen/common/rcupdate.c index ed9083d2b2..5e7bd7196f 100644 --- a/xen/common/rcupdate.c +++ b/xen/common/rcupdate.c @@ -46,6 +46,8 @@ #include #include +DEFINE_PER_CPU(unsigned int, rcu_lock_cnt); + /* Global control variables for rcupdate callback mechanism. */ static struct rcu_ctrlblk { long cur; /* Current batch number. */ diff --git a/xen/common/softirq.c b/xen/common/softirq.c index 00d676b62c..eba65c5fc0 100644 --- a/xen/common/softirq.c +++ b/xen/common/softirq.c @@ -31,6 +31,8 @@ static void __do_softirq(unsigned long ignore_mask) unsigned long pending; bool rcu_allowed = !(ignore_mask & (1ul << RCU_SOFTIRQ)); + ASSERT(!rcu_allowed || rcu_quiesce_allowed()); + for ( ; ; ) { /* @@ -58,7 +60,7 @@ void process_pending_softirqs(void) (1ul << SCHED_SLAVE_SOFTIRQ); /* Block RCU processing in case of rcu_read_lock() held. */ - if ( preempt_count() ) + if ( !rcu_quiesce_allowed() ) ignore_mask |= 1ul << RCU_SOFTIRQ; ASSERT(!in_irq() && local_irq_is_enabled()); diff --git a/xen/include/xen/rcupdate.h b/xen/include/xen/rcupdate.h index 31c8b86d13..d3c2b7b093 100644 --- a/xen/include/xen/rcupdate.h +++ b/xen/include/xen/rcupdate.h @@ -32,12 +32,35 @@ #define __XEN_RCUPDATE_H #include +#include #include #include +#include #include #define __rcu +DECLARE_PER_CPU(unsigned int, rcu_lock_cnt); + +static inline void rcu_quiesce_disable(void) +{ + preempt_disable(); + this_cpu(rcu_lock_cnt)++; + barrier(); +} + +static inline void rcu_quiesce_enable(void) +{ + barrier(); + this_cpu(rcu_lock_cnt)--; + preempt_enable(); +} + +static inline bool rcu_quiesce_allowed(void) +{ + return !this_cpu(rcu_lock_cnt); +} + /** * struct rcu_head - callback structure for use with RCU * @next: next update requests in a list @@ -91,16 +114,23 @@ typedef struct _rcu_read_lock rcu_read_lock_t; * will be deferred until the outermost RCU read-side critical section * completes. * - * It is illegal to block while in an RCU read-side critical section. + * It is illegal to process softirqs while in an RCU read-side critical section. */ -#define rcu_read_lock(x) ({ ((void)(x)); preempt_disable(); }) +static inline void rcu_read_lock(rcu_read_lock_t *lock) +{ + rcu_quiesce_disable(); +} /** * rcu_read_unlock - marks the end of an RCU read-side critical section. * * See rcu_read_lock() for more information. */ -#define rcu_read_unlock(x) ({ ((void)(x)); preempt_enable(); }) +static inline void rcu_read_unlock(rcu_read_lock_t *lock) +{ + ASSERT(!rcu_quiesce_allowed()); + rcu_quiesce_enable(); +} /* * So where is rcu_write_lock()? It does not exist, as there is no From patchwork Fri Mar 13 13:06:14 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: =?utf-8?b?SsO8cmdlbiBHcm/Dnw==?= X-Patchwork-Id: 11436873 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 048A51668 for ; Fri, 13 Mar 2020 13:07:45 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DFDF720746 for ; Fri, 13 Mar 2020 13:07:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DFDF720746 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jCk1B-00019D-T6; Fri, 13 Mar 2020 13:06:25 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jCk1A-00018w-5B for xen-devel@lists.xenproject.org; Fri, 13 Mar 2020 13:06:24 +0000 X-Inumbo-ID: 6c6a5ebd-652b-11ea-b2f0-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 6c6a5ebd-652b-11ea-b2f0-12813bfff9fa; Fri, 13 Mar 2020 13:06:18 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 673FEAFCA; Fri, 13 Mar 2020 13:06:17 +0000 (UTC) From: Juergen Gross To: xen-devel@lists.xenproject.org Date: Fri, 13 Mar 2020 14:06:14 +0100 Message-Id: <20200313130614.27265-5-jgross@suse.com> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20200313130614.27265-1-jgross@suse.com> References: <20200313130614.27265-1-jgross@suse.com> Subject: [Xen-devel] [PATCH v6 4/4] xen/rcu: add per-lock counter in debug builds X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Stefano Stabellini , Julien Grall , Wei Liu , Andrew Cooper , Ian Jackson , George Dunlap , Jan Beulich MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Add a lock specific counter to rcu read locks in debug builds. This allows to test for matching lock/unlock calls. This will help to avoid cases like the one fixed by commit 98ed1f43cc2c89 where different rcu read locks were referenced in the lock and unlock calls. Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich --- V5: - updated commit message (Jan Beulich) --- xen/include/xen/rcupdate.h | 46 +++++++++++++++++++++++++++++++++------------- 1 file changed, 33 insertions(+), 13 deletions(-) diff --git a/xen/include/xen/rcupdate.h b/xen/include/xen/rcupdate.h index d3c2b7b093..e0c3b16e7d 100644 --- a/xen/include/xen/rcupdate.h +++ b/xen/include/xen/rcupdate.h @@ -37,21 +37,50 @@ #include #include #include +#include #define __rcu +#ifndef NDEBUG +/* * Lock type for passing to rcu_read_{lock,unlock}. */ +struct _rcu_read_lock { + atomic_t cnt; +}; +typedef struct _rcu_read_lock rcu_read_lock_t; +#define DEFINE_RCU_READ_LOCK(x) rcu_read_lock_t x = { .cnt = ATOMIC_INIT(0) } +#define RCU_READ_LOCK_INIT(x) atomic_set(&(x)->cnt, 0) + +#else +/* + * Dummy lock type for passing to rcu_read_{lock,unlock}. Currently exists + * only to document the reason for rcu_read_lock() critical sections. + */ +struct _rcu_read_lock {}; +typedef struct _rcu_read_lock rcu_read_lock_t; +#define DEFINE_RCU_READ_LOCK(x) rcu_read_lock_t x +#define RCU_READ_LOCK_INIT(x) + +#endif + DECLARE_PER_CPU(unsigned int, rcu_lock_cnt); -static inline void rcu_quiesce_disable(void) +static inline void rcu_quiesce_disable(rcu_read_lock_t *lock) { preempt_disable(); this_cpu(rcu_lock_cnt)++; +#ifndef NDEBUG + atomic_inc(&lock->cnt); +#endif barrier(); } -static inline void rcu_quiesce_enable(void) +static inline void rcu_quiesce_enable(rcu_read_lock_t *lock) { barrier(); +#ifndef NDEBUG + ASSERT(atomic_read(&lock->cnt)); + atomic_dec(&lock->cnt); +#endif this_cpu(rcu_lock_cnt)--; preempt_enable(); } @@ -81,15 +110,6 @@ struct rcu_head { int rcu_pending(int cpu); int rcu_needs_cpu(int cpu); -/* - * Dummy lock type for passing to rcu_read_{lock,unlock}. Currently exists - * only to document the reason for rcu_read_lock() critical sections. - */ -struct _rcu_read_lock {}; -typedef struct _rcu_read_lock rcu_read_lock_t; -#define DEFINE_RCU_READ_LOCK(x) rcu_read_lock_t x -#define RCU_READ_LOCK_INIT(x) - /** * rcu_read_lock - mark the beginning of an RCU read-side critical section. * @@ -118,7 +138,7 @@ typedef struct _rcu_read_lock rcu_read_lock_t; */ static inline void rcu_read_lock(rcu_read_lock_t *lock) { - rcu_quiesce_disable(); + rcu_quiesce_disable(lock); } /** @@ -129,7 +149,7 @@ static inline void rcu_read_lock(rcu_read_lock_t *lock) static inline void rcu_read_unlock(rcu_read_lock_t *lock) { ASSERT(!rcu_quiesce_allowed()); - rcu_quiesce_enable(); + rcu_quiesce_enable(lock); } /*