98 lines
2.9 KiB
Diff
98 lines
2.9 KiB
Diff
From 1db4ce56001465fba240916d0c8de7443cafec62 Mon Sep 17 00:00:00 2001
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Wed, 25 Feb 2015 12:16:43 +0100
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Subject: [PATCH] Revert "rwsem-rt: Do not allow readers to nest"
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.0/patches-4.0.5-rt3.tar.xz
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This behaviour is required by cpufreq and its logic is "okay": It does a
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read_lock followed by a try_read_lock.
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Lockdep warns if one try a read_lock twice in -RT and vanilla so it
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should be good. We still only allow multiple readers as long as it is in
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the same process.
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Cc: stable-rt@vger.kernel.org
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/rwsem_rt.h | 1 +
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kernel/locking/rt.c | 29 +++++++++++++++++++++++------
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2 files changed, 24 insertions(+), 6 deletions(-)
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--- a/include/linux/rwsem_rt.h
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+++ b/include/linux/rwsem_rt.h
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@@ -20,6 +20,7 @@
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struct rw_semaphore {
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struct rt_mutex lock;
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+ int read_depth;
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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#endif
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--- a/kernel/locking/rt.c
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+++ b/kernel/locking/rt.c
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@@ -316,7 +316,8 @@ EXPORT_SYMBOL(rt_up_write);
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void rt_up_read(struct rw_semaphore *rwsem)
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{
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rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
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- rt_mutex_unlock(&rwsem->lock);
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+ if (--rwsem->read_depth == 0)
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+ rt_mutex_unlock(&rwsem->lock);
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}
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EXPORT_SYMBOL(rt_up_read);
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@@ -327,6 +328,7 @@ EXPORT_SYMBOL(rt_up_read);
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void rt_downgrade_write(struct rw_semaphore *rwsem)
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{
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BUG_ON(rt_mutex_owner(&rwsem->lock) != current);
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+ rwsem->read_depth = 1;
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}
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EXPORT_SYMBOL(rt_downgrade_write);
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@@ -356,12 +358,23 @@ EXPORT_SYMBOL(rt_down_write_nested);
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int rt_down_read_trylock(struct rw_semaphore *rwsem)
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{
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- int ret;
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+ struct rt_mutex *lock = &rwsem->lock;
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+ int ret = 1;
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- ret = rt_mutex_trylock(&rwsem->lock);
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- if (ret)
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- rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
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+ /*
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+ * recursive read locks succeed when current owns the rwsem,
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+ * but not when read_depth == 0 which means that the rwsem is
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+ * write locked.
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+ */
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+ if (rt_mutex_owner(lock) != current)
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+ ret = rt_mutex_trylock(&rwsem->lock);
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+ else if (!rwsem->read_depth)
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+ ret = 0;
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+ if (ret) {
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+ rwsem->read_depth++;
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+ rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
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+ }
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return ret;
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}
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EXPORT_SYMBOL(rt_down_read_trylock);
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@@ -371,7 +384,10 @@ static void __rt_down_read(struct rw_sem
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struct rt_mutex *lock = &rwsem->lock;
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rwsem_acquire_read(&rwsem->dep_map, subclass, 0, _RET_IP_);
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- rt_mutex_lock(&rwsem->lock);
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+
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+ if (rt_mutex_owner(lock) != current)
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+ rt_mutex_lock(&rwsem->lock);
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+ rwsem->read_depth++;
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}
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void rt_down_read(struct rw_semaphore *rwsem)
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@@ -396,6 +412,7 @@ void __rt_rwsem_init(struct rw_semaphor
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debug_check_no_locks_freed((void *)rwsem, sizeof(*rwsem));
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lockdep_init_map(&rwsem->dep_map, name, key, 0);
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#endif
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+ rwsem->read_depth = 0;
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rwsem->lock.save_state = 0;
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}
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EXPORT_SYMBOL(__rt_rwsem_init);
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