From: Steven Rostedt Subject: [PATCH RT 1/2] rwsem-rt: Do not allow readers to nest Date: Tue, 08 Apr 2014 22:47:01 -0400 Message-ID: <20140409025231.998774075@goodmis.org> References: <20140409024700.702797305@goodmis.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Thomas Gleixner , Carsten Emde , Sebastian Andrzej Siewior , John Kacur , Paul Gortmaker , Peter Zijlstra , "H. Peter Anvin" To: linux-kernel@vger.kernel.org, linux-rt-users Return-path: Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.227]:23775 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757406AbaDICwg (ORCPT ); Tue, 8 Apr 2014 22:52:36 -0400 Content-Disposition: inline; filename=0001-rwsem-rt-Do-not-allow-readers-to-nest.patch Sender: linux-rt-users-owner@vger.kernel.org List-ID: From: "Steven Rostedt (Red Hat)" The readers of mainline rwsems are not allowed to nest, the rwsems in the PREEMPT_RT kernel should not nest either. Signed-off-by: Steven Rostedt --- include/linux/rwsem_rt.h | 1 - kernel/rt.c | 37 ++++++++----------------------------- 2 files changed, 8 insertions(+), 30 deletions(-) diff --git a/include/linux/rwsem_rt.h b/include/linux/rwsem_rt.h index e94d945..a81151c 100644 --- a/include/linux/rwsem_rt.h +++ b/include/linux/rwsem_rt.h @@ -20,7 +20,6 @@ struct rw_semaphore { struct rt_mutex lock; - int read_depth; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif diff --git a/kernel/rt.c b/kernel/rt.c index 5d17727..bb72347 100644 --- a/kernel/rt.c +++ b/kernel/rt.c @@ -316,10 +316,8 @@ EXPORT_SYMBOL(rt_up_write); void rt_up_read(struct rw_semaphore *rwsem) { - if (--rwsem->read_depth == 0) { - rwsem_release(&rwsem->dep_map, 1, _RET_IP_); - rt_mutex_unlock(&rwsem->lock); - } + rwsem_release(&rwsem->dep_map, 1, _RET_IP_); + rt_mutex_unlock(&rwsem->lock); } EXPORT_SYMBOL(rt_up_read); @@ -330,7 +328,6 @@ EXPORT_SYMBOL(rt_up_read); void rt_downgrade_write(struct rw_semaphore *rwsem) { BUG_ON(rt_mutex_owner(&rwsem->lock) != current); - rwsem->read_depth = 1; } EXPORT_SYMBOL(rt_downgrade_write); @@ -367,37 +364,20 @@ void rt_down_write_nested_lock(struct rw_semaphore *rwsem, int rt_down_read_trylock(struct rw_semaphore *rwsem) { - struct rt_mutex *lock = &rwsem->lock; - int ret = 1; - - /* - * recursive read locks succeed when current owns the rwsem, - * but not when read_depth == 0 which means that the rwsem is - * write locked. - */ - if (rt_mutex_owner(lock) != current) { - ret = rt_mutex_trylock(&rwsem->lock); - if (ret) - rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_); - } else if (!rwsem->read_depth) { - ret = 0; - } + int ret; + ret = rt_mutex_trylock(&rwsem->lock); if (ret) - rwsem->read_depth++; + rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_); + return ret; } EXPORT_SYMBOL(rt_down_read_trylock); static void __rt_down_read(struct rw_semaphore *rwsem, int subclass) { - struct rt_mutex *lock = &rwsem->lock;