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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org,
	linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	John Kacur <jkacur@redhat.com>,
	Paul Gortmaker <paul.gortmaker@windriver.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH RT 1/2] rwsem-rt: Do not allow readers to nest
Date: Tue, 08 Apr 2014 22:47:01 -0400	[thread overview]
Message-ID: <20140409025231.998774075@goodmis.org> (raw)
In-Reply-To: 20140409024700.702797305@goodmis.org

[-- Attachment #1: 0001-rwsem-rt-Do-not-allow-readers-to-nest.patch --]
[-- Type: text/plain, Size: 2834 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

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 <rostedt@goodmis.org>
---
 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;
-
-	if (rt_mutex_owner(lock) != current) {
-		rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_);
-		rt_mutex_lock(&rwsem->lock);
-	}
-	rwsem->read_depth++;
+	rwsem_acquire(&rwsem->dep_map, subclass, 0, _RET_IP_);
+	rt_mutex_lock(&rwsem->lock);
 }
 
 void  rt_down_read(struct rw_semaphore *rwsem)
@@ -422,7 +402,6 @@ void  __rt_rwsem_init(struct rw_semaphore *rwsem, const char *name,
 	debug_check_no_locks_freed((void *)rwsem, sizeof(*rwsem));
 	lockdep_init_map(&rwsem->dep_map, name, key, 0);
 #endif
-	rwsem->read_depth = 0;
 	rwsem->lock.save_state = 0;
 }
 EXPORT_SYMBOL(__rt_rwsem_init);
-- 
1.8.5.3



WARNING: multiple messages have this Message-ID (diff)
From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org,
	linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	John Kacur <jkacur@redhat.com>,
	Paul Gortmaker <paul.gortmaker@windriver.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH RT 1/2] rwsem-rt: Do not allow readers to nest
Date: Tue, 08 Apr 2014 22:47:01 -0400	[thread overview]
Message-ID: <20140409025231.998774075@goodmis.org> (raw)
In-Reply-To: 20140409024700.702797305@goodmis.org

[-- Attachment #1: 0001-rwsem-rt-Do-not-allow-readers-to-nest.patch --]
[-- Type: text/plain, Size: 2220 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

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 <rostedt@goodmis.org>
---
 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;

  reply	other threads:[~2014-04-09  2:52 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-09  2:47 [PATCH RT 0/2] rwsem-rt: Make rwsem rt closer to mainline Steven Rostedt
2014-04-09  2:47 ` Steven Rostedt [this message]
2014-04-09  2:47   ` [PATCH RT 1/2] rwsem-rt: Do not allow readers to nest Steven Rostedt
2014-05-02  9:04   ` Sebastian Andrzej Siewior
2015-02-18 19:57   ` Sebastian Andrzej Siewior
2015-02-18 20:13     ` Steven Rostedt
2015-02-20  5:07       ` Jason Low
2015-02-25 12:15       ` Sebastian Andrzej Siewior
2014-04-09  2:47 ` [PATCH RT 2/2] rtmutex: Remove duplicate rt_mutex_init() Steven Rostedt
2014-04-09  2:47   ` Steven Rostedt
2014-05-02  9:08   ` Sebastian Andrzej Siewior
2014-05-02 13:12     ` Steven Rostedt
2014-05-02 13:21       ` Sebastian Andrzej Siewior

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