Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757046AbaFSCVA (ORCPT ); Wed, 18 Jun 2014 22:21:00 -0400 Received: from mail-qg0-f48.google.com ([209.85.192.48]:43195 "EHLO mail-qg0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754662AbaFSCU7 (ORCPT ); Wed, 18 Jun 2014 22:20:59 -0400 Date: Wed, 18 Jun 2014 22:20:55 -0400 From: Tejun Heo To: cl@linux-foundation.org, kmo@daterainc.com Cc: linux-kernel@vger.kernel.org Subject: [PATCH v2 6/6] percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is_zero() Message-ID: <20140619022055.GD20100@mtj.dyndns.org> References: <1403053685-28240-1-git-send-email-tj@kernel.org> <1403053685-28240-7-git-send-email-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1403053685-28240-7-git-send-email-tj@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that explicit invocation of percpu_ref_exit() is necessary to free the percpu counter, we can implement percpu_ref_reinit() which reinitializes a released percpu_ref. This can be used implement scalable gating switch which can be drained and then re-opened without worrying about memory allocation failures. percpu_ref_is_zero() is added to be used in a sanity check in percpu_ref_exit(). As this function will be useful for other purposes too, make it a public interface. v2: Use smp_read_barrier_depends() instead of smp_load_acquire(). We only need data dep barrier and smp_load_acquire() is stronger and heavier on some archs. Spotted by Lai Jiangshan. Signed-off-by: Tejun Heo Cc: Kent Overstreet Cc: Christoph Lameter Cc: Lai Jiangshan --- include/linux/percpu-refcount.h | 19 +++++++++++++++++++ lib/percpu-refcount.c | 35 +++++++++++++++++++++++++++++++++++ 2 files changed, 54 insertions(+) --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -67,6 +67,7 @@ struct percpu_ref { int __must_check percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release); +void percpu_ref_reinit(struct percpu_ref *ref); void percpu_ref_exit(struct percpu_ref *ref); void percpu_ref_kill_and_confirm(struct percpu_ref *ref, percpu_ref_func_t *confirm_kill); @@ -99,6 +100,9 @@ static inline bool __pcpu_ref_alive(stru { unsigned long pcpu_ptr = ACCESS_ONCE(ref->pcpu_count_ptr); + /* paired with smp_store_release() in percpu_ref_reinit() */ + smp_read_barrier_depends(); + if (unlikely(pcpu_ptr & PCPU_REF_DEAD)) return false; @@ -206,4 +210,19 @@ static inline void percpu_ref_put(struct rcu_read_unlock_sched(); } +/** + * percpu_ref_is_zero - test whether a percpu refcount reached zero + * @ref: percpu_ref to test + * + * Returns %true if @ref reached zero. + */ +static inline bool percpu_ref_is_zero(struct percpu_ref *ref) +{ + unsigned __percpu *pcpu_count; + + if (__pcpu_ref_alive(ref, &pcpu_count)) + return false; + return !atomic_read(&ref->count); +} + #endif --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -61,6 +61,41 @@ int percpu_ref_init(struct percpu_ref *r EXPORT_SYMBOL_GPL(percpu_ref_init); /** + * percpu_ref_reinit - re-initialize a percpu refcount + * @ref: perpcu_ref to re-initialize + * + * Re-initialize @ref so that it's in the same state as when it finished + * percpu_ref_init(). @ref must have been initialized successfully, killed + * and reached 0 but not exited. + * + * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while + * this function is in progress. + */ +void percpu_ref_reinit(struct percpu_ref *ref) +{ + unsigned __percpu *pcpu_count = pcpu_count_ptr(ref); + int cpu; + + BUG_ON(!pcpu_count); + WARN_ON(!percpu_ref_is_zero(ref)); + + atomic_set(&ref->count, 1 + PCPU_COUNT_BIAS); + + /* + * Restore per-cpu operation. smp_store_release() is paired with + * smp_load_acquire() in __pcpu_ref_alive() and guarantees that the + * zeroing is visible to all percpu accesses which can see the + * following PCPU_REF_DEAD clearing. + */ + for_each_possible_cpu(cpu) + *per_cpu_ptr(pcpu_count, cpu) = 0; + + smp_store_release(&ref->pcpu_count_ptr, + ref->pcpu_count_ptr & ~PCPU_REF_DEAD); +} +EXPORT_SYMBOL_GPL(percpu_ref_reinit); + +/** * percpu_ref_exit - undo percpu_ref_init() * @ref: percpu_ref to exit * -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/