From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752826Ab3JUWfJ (ORCPT ); Mon, 21 Oct 2013 18:35:09 -0400 Received: from mail-ee0-f47.google.com ([74.125.83.47]:49474 "EHLO mail-ee0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752120Ab3JUWdz (ORCPT ); Mon, 21 Oct 2013 18:33:55 -0400 From: David Herrmann To: dri-devel@lists.freedesktop.org Cc: linux-kernel@vger.kernel.org, Dave Airlie , David Herrmann Subject: [RFC v2 2/6] percpu_rw_semaphore: add percpu_down_read_trylock() Date: Tue, 22 Oct 2013 00:33:24 +0200 Message-Id: <1382394808-20611-3-git-send-email-dh.herrmann@gmail.com> X-Mailer: git-send-email 1.8.4.1 In-Reply-To: <1382394808-20611-1-git-send-email-dh.herrmann@gmail.com> References: <1382394808-20611-1-git-send-email-dh.herrmann@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is basically a copy of percpu_down_read() but does not sleep if a writer is already active. Same semantics as classic down_read_trylock(). Signed-off-by: David Herrmann --- include/linux/percpu-rwsem.h | 1 + lib/percpu-rwsem.c | 20 ++++++++++++++++++++ 2 files changed, 21 insertions(+) diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h index 3e88c9a..2f752bd 100644 --- a/include/linux/percpu-rwsem.h +++ b/include/linux/percpu-rwsem.h @@ -16,6 +16,7 @@ struct percpu_rw_semaphore { }; extern void percpu_down_read(struct percpu_rw_semaphore *); +extern int percpu_down_read_trylock(struct percpu_rw_semaphore *); extern void percpu_up_read(struct percpu_rw_semaphore *); extern void percpu_down_write(struct percpu_rw_semaphore *); diff --git a/lib/percpu-rwsem.c b/lib/percpu-rwsem.c index 893586c..596f44b 100644 --- a/lib/percpu-rwsem.c +++ b/lib/percpu-rwsem.c @@ -92,6 +92,26 @@ void percpu_down_read(struct percpu_rw_semaphore *brw) } EXPORT_SYMBOL(percpu_down_read); +int percpu_down_read_trylock(struct percpu_rw_semaphore *brw) +{ + int r; + + if (likely(update_fast_ctr(brw, +1))) { + rwsem_acquire_read(&brw->rw_sem.dep_map, 0, 0, _RET_IP_); + return 1; + } + + r = down_read_trylock(&brw->rw_sem); + if (r) { + atomic_inc(&brw->slow_read_ctr); + /* avoid up_read()->rwsem_release() */ + __up_read(&brw->rw_sem); + } + + return r; +} +EXPORT_SYMBOL(percpu_down_read_trylock); + void percpu_up_read(struct percpu_rw_semaphore *brw) { rwsem_release(&brw->rw_sem.dep_map, 1, _RET_IP_); -- 1.8.4.1