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The changes to move the migrate_disable() down in the trylocks()
caused race conditions to appear in the cpu hotplug code. The
migrate disables must be done before any of the rtmutexes are
taken, otherwise a lock may be held that prevents hotplug from
moving forward.
Link: http://lkml.kernel.org/r/20140429201308.63292691@gandalf.local.home
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Nicholas Mc Guire <der.herr@hofr.at>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
Cc: Clark Williams <williams@redhat.com>
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rwlocks and rwsems on RT do not allow multiple readers. Annotate the
lockdep acquire functions accordingly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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pushdown of migrate_disable/enable from read_*lock* to the rt_read_*lock*
api level
general mapping to mutexes:
read_*lock*
`-> rt_read_*lock*
`-> __spin_lock (the sleeping spin locks)
`-> rt_mutex
The real read_lock* mapping:
read_lock_irqsave -.
read_lock_irq `-> rt_read_lock_irqsave()
`->read_lock ---------. \
read_lock_bh ------+ \
`--> rt_read_lock()
if (rt_mutex_owner(lock) != current){
`-> __rt_spin_lock()
rt_spin_lock_fastlock()
`->rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_trylock mapping:
read_trylock
`-> rt_read_trylock
if (rt_mutex_owner(lock) != current){
`-> rt_mutex_trylock()
rt_mutex_fasttrylock()
rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_unlock* mapping:
read_unlock_bh --------+
read_unlock_irq -------+
read_unlock_irqrestore +
read_unlock -----------+
`-> rt_read_unlock()
if(--rwlock->read_depth==0){
`-> __rt_spin_unlock()
rt_spin_lock_fastunlock()
`-> rt_mutex_cmpxchg()
migrate_disable()
}
So calls to migrate_disable/enable() are better placed at the rt_read_*
level of lock/trylock/unlock as all of the read_*lock* API has this as a
common path. In the rt_read* API of lock/trylock/unlock the nesting level
is already being recorded in rwlock->read_depth, so we can push down the
migrate disable/enable to that level and condition it on the read_depth
going from 0 to 1 -> migrate_disable and 1 to 0 -> migrate_enable. This
eliminates the recursive calls that were needed when migrate_disable/enable
was done at the read_*lock* level.
The approach to read_*_bh also eliminates the concerns raised with the
regards to api inbalances (read_lock_bh -> read_unlock+local_bh_enable)
Tested-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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pushdown of migrate_disable/enable from write_*lock* to the rt_write_*lock*
api level
general mapping of write_*lock* to mutexes:
write_*lock*
`-> rt_write_*lock*
`-> __spin_lock (the sleeping __spin_lock)
`-> rt_mutex
write_*lock*s are non-recursive so we have two lock chains to consider
- write_trylock*/write_unlock
- write_lock*/wirte_unlock
for both paths the migration_disable/enable must be balanced.
write_trylock* mapping:
write_trylock_irqsave
`-> rt_write_trylock_irqsave
write_trylock \
`--------> rt_write_trylock
ret = rt_mutex_trylock
rt_mutex_fasttrylock
rt_mutex_cmpxchg
if (ret)
migrate_disable
write_lock* mapping:
write_lock_irqsave
`-> rt_write_lock_irqsave
write_lock_irq -> write_lock ----. \
write_lock_bh -+ \
`-> rt_write_lock
__rt_spin_lock()
rt_spin_lock_fastlock()
rt_mutex_cmpxchg()
migrate_disable()
write_unlock* mapping:
write_unlock_irqrestore.
write_unlock_bh -------+
write_unlock_irq -> write_unlock ----------+
`-> rt_write_unlock()
__rt_spin_unlock()
rt_spin_lock_fastunlock()
rt_mutex_cmpxchg()
migrate_enable()
So calls to migrate_disable/enable() are better placed at the rt_write_*
level of lock/trylock/unlock as all of the write_*lock* API has this as a
common path.
This approach to write_*_bh also eliminates the concerns raised with
regards to api inbalances (write_lock_bh -> write_unlock+local_bh_enable)
Tested-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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No need to unconditionally migrate_disable (what is it protecting ?) and
re-enable on failure to acquire the lock.
This patch moves the migrate_disable to be conditioned on sucessful lock
acquisition only.
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Map spinlocks, rwlocks, rw_semaphores and semaphores to the rt_mutex
based locking functions for preempt-rt.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
|
|
rwlocks and rwsems on RT do not allow multiple readers. Annotate the
lockdep acquire functions accordingly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
|
|
pushdown of migrate_disable/enable from read_*lock* to the rt_read_*lock*
api level
general mapping to mutexes:
read_*lock*
`-> rt_read_*lock*
`-> __spin_lock (the sleeping spin locks)
`-> rt_mutex
The real read_lock* mapping:
read_lock_irqsave -.
read_lock_irq `-> rt_read_lock_irqsave()
`->read_lock ---------. \
read_lock_bh ------+ \
`--> rt_read_lock()
if (rt_mutex_owner(lock) != current){
`-> __rt_spin_lock()
rt_spin_lock_fastlock()
`->rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_trylock mapping:
read_trylock
`-> rt_read_trylock
if (rt_mutex_owner(lock) != current){
`-> rt_mutex_trylock()
rt_mutex_fasttrylock()
rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_unlock* mapping:
read_unlock_bh --------+
read_unlock_irq -------+
read_unlock_irqrestore +
read_unlock -----------+
`-> rt_read_unlock()
if(--rwlock->read_depth==0){
`-> __rt_spin_unlock()
rt_spin_lock_fastunlock()
`-> rt_mutex_cmpxchg()
migrate_disable()
}
So calls to migrate_disable/enable() are better placed at the rt_read_*
level of lock/trylock/unlock as all of the read_*lock* API has this as a
common path. In the rt_read* API of lock/trylock/unlock the nesting level
is already being recorded in rwlock->read_depth, so we can push down the
migrate disable/enable to that level and condition it on the read_depth
going from 0 to 1 -> migrate_disable and 1 to 0 -> migrate_enable. This
eliminates the recursive calls that were needed when migrate_disable/enable
was done at the read_*lock* level.
The approach to read_*_bh also eliminates the concerns raised with the
regards to api inbalances (read_lock_bh -> read_unlock+local_bh_enable)
Tested-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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pushdown of migrate_disable/enable from write_*lock* to the rt_write_*lock*
api level
general mapping of write_*lock* to mutexes:
write_*lock*
`-> rt_write_*lock*
`-> __spin_lock (the sleeping __spin_lock)
`-> rt_mutex
write_*lock*s are non-recursive so we have two lock chains to consider
- write_trylock*/write_unlock
- write_lock*/wirte_unlock
for both paths the migration_disable/enable must be balanced.
write_trylock* mapping:
write_trylock_irqsave
`-> rt_write_trylock_irqsave
write_trylock \
`--------> rt_write_trylock
ret = rt_mutex_trylock
rt_mutex_fasttrylock
rt_mutex_cmpxchg
if (ret)
migrate_disable
write_lock* mapping:
write_lock_irqsave
`-> rt_write_lock_irqsave
write_lock_irq -> write_lock ----. \
write_lock_bh -+ \
`-> rt_write_lock
__rt_spin_lock()
rt_spin_lock_fastlock()
rt_mutex_cmpxchg()
migrate_disable()
write_unlock* mapping:
write_unlock_irqrestore.
write_unlock_bh -------+
write_unlock_irq -> write_unlock ----------+
`-> rt_write_unlock()
__rt_spin_unlock()
rt_spin_lock_fastunlock()
rt_mutex_cmpxchg()
migrate_enable()
So calls to migrate_disable/enable() are better placed at the rt_write_*
level of lock/trylock/unlock as all of the write_*lock* API has this as a
common path.
This approach to write_*_bh also eliminates the concerns raised with
regards to api inbalances (write_lock_bh -> write_unlock+local_bh_enable)
Tested-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
No need to unconditionally migrate_disable (what is it protecting ?) and
re-enable on failure to acquire the lock.
This patch moves the migrate_disable to be conditioned on sucessful lock
acquisition only.
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Map spinlocks, rwlocks, rw_semaphores and semaphores to the rt_mutex
based locking functions for preempt-rt.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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