CPU bringup calls into the random pool to initialize the stack
canary. During boot that works nicely even on RT as the might sleep
checks are disabled. During CPU hotplug the might sleep checks
trigger. Making the locks in random raw is a major PITA, so avoid the
call on RT is the only sensible solution. This is basically the same
randomness which we get during boot where the random pool has no
entropy and we rely on the TSC randomnness.
Reported-by: Carsten Emde <carsten.emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
We had a customer report a lockup on a 3.0-rt kernel that had the
following backtrace:
[ffff88107fca3e80] rt_spin_lock_slowlock at ffffffff81499113
[ffff88107fca3f40] rt_spin_lock at ffffffff81499a56
[ffff88107fca3f50] __wake_up at ffffffff81043379
[ffff88107fca3f80] mce_notify_irq at ffffffff81017328
[ffff88107fca3f90] intel_threshold_interrupt at ffffffff81019508
[ffff88107fca3fa0] smp_threshold_interrupt at ffffffff81019fc1
[ffff88107fca3fb0] threshold_interrupt at ffffffff814a1853
It actually bugged because the lock was taken by the same owner that
already had that lock. What happened was the thread that was setting
itself on a wait queue had the lock when an MCE triggered. The MCE
interrupt does a wake up on its wait list and grabs the same lock.
NOTE: THIS IS NOT A BUG ON MAINLINE
Sorry for yelling, but as I Cc'd mainline maintainers I want them to
know that this is an PREEMPT_RT bug only. I only Cc'd them for advice.
On PREEMPT_RT the wait queue locks are converted from normal
"spin_locks" into an rt_mutex (see the rt_spin_lock_slowlock above).
These are not to be taken by hard interrupt context. This usually isn't
a problem as most all interrupts in PREEMPT_RT are converted into
schedulable threads. Unfortunately that's not the case with the MCE irq.
As wait queue locks are notorious for long hold times, we can not
convert them to raw_spin_locks without causing issues with -rt. But
Thomas has created a "simple-wait" structure that uses raw spin locks
which may have been a good fit.
Unfortunately, wait queues are not the only issue, as the mce_notify_irq
also does a schedule_work(), which grabs the workqueue spin locks that
have the exact same issue.
Thus, this patch I'm proposing is to move the actual work of the MCE
interrupt into a helper thread that gets woken up on the MCE interrupt
and does the work in a schedulable context.
NOTE: THIS PATCH ONLY CHANGES THE BEHAVIOR WHEN PREEMPT_RT IS SET
Oops, sorry for yelling again, but I want to stress that I keep the same
behavior of mainline when PREEMPT_RT is not set. Thus, this only changes
the MCE behavior when PREEMPT_RT is configured.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bigeasy@linutronix: make mce_notify_work() a proper prototype, use
kthread_run()]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
mce_timer is started in atomic contexts of cpu bringup. This results
in might_sleep() warnings on RT. Convert mce_timer to a hrtimer to
avoid this.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
fold in:
|From: Mike Galbraith <bitbucket@online.de>
|Date: Wed, 29 May 2013 13:52:13 +0200
|Subject: [PATCH] x86/mce: fix mce timer interval
|
|Seems mce timer fire at the wrong frequency in -rt kernels since roughly
|forever due to 32 bit overflow. 3.8-rt is also missing a multiplier.
|
|Add missing us -> ns conversion and 32 bit overflow prevention.
|
|Signed-off-by: Mike Galbraith <bitbucket@online.de>
|[bigeasy: use ULL instead of u64 cast]
|Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Two cps in parallel managed to stall the the ext4 fs. It seems that
journal code is either waiting for locks or sleeping waiting for
something to happen. This seems similar to what Mike observed on ext3,
here is his description:
|With an -rt kernel, and a heavy sync IO load, tasks can jam
|up on journal locks without unplugging, which can lead to
|terminal IO starvation. Unplug and schedule when waiting
|for space.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
With an -rt kernel, and a heavy sync IO load, tasks can jam
up on journal locks without unplugging, which can lead to
terminal IO starvation. Unplug and schedule when waiting for space.
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Theodore Tso <tytso@mit.edu>
Link: http://lkml.kernel.org/r/1341812414.7370.73.camel@marge.simpson.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
User preempt_*_rt instead of local_irq_*_rt or otherwise there will be
warning on ARM like below:
WARNING: at build/linux/kernel/smp.c:459 smp_call_function_many+0x98/0x264()
Modules linked in:
[<c0013bb4>] (unwind_backtrace+0x0/0xe4) from [<c001be94>] (warn_slowpath_common+0x4c/0x64)
[<c001be94>] (warn_slowpath_common+0x4c/0x64) from [<c001bec4>] (warn_slowpath_null+0x18/0x1c)
[<c001bec4>] (warn_slowpath_null+0x18/0x1c) from [<c0053ff8>](smp_call_function_many+0x98/0x264)
[<c0053ff8>] (smp_call_function_many+0x98/0x264) from [<c0054364>] (smp_call_function+0x44/0x6c)
[<c0054364>] (smp_call_function+0x44/0x6c) from [<c0017d50>] (__new_context+0xbc/0x124)
[<c0017d50>] (__new_context+0xbc/0x124) from [<c009e49c>] (flush_old_exec+0x460/0x5e4)
[<c009e49c>] (flush_old_exec+0x460/0x5e4) from [<c00d61ac>] (load_elf_binary+0x2e0/0x11ac)
[<c00d61ac>] (load_elf_binary+0x2e0/0x11ac) from [<c009d060>] (search_binary_handler+0x94/0x2a4)
[<c009d060>] (search_binary_handler+0x94/0x2a4) from [<c009e8fc>] (do_execve+0x254/0x364)
[<c009e8fc>] (do_execve+0x254/0x364) from [<c0010e84>] (sys_execve+0x34/0x54)
[<c0010e84>] (sys_execve+0x34/0x54) from [<c000da00>] (ret_fast_syscall+0x0/0x30)
---[ end trace 0000000000000002 ]---
The reason is that ARM need irq enabled when doing activate_mm().
According to mm-protect-activate-switch-mm.patch, actually
preempt_[disable|enable]_rt() is sufficient.
Inspired-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1337061236-1766-1-git-send-email-yong.zhang0@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
On RT we cannot loop with preemption disabled here as
mnt_make_readonly() might have been preempted. We can safely enable
preemption while waiting for MNT_WRITE_HOLD to be cleared. Safe on !RT
as well.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Beyond the warning:
drivers/tty/serial/8250/8250.c:1613:6: warning: unused variable ‘pass_counter’ [-Wunused-variable]
the solution of just looping infinitely was ugly - up it to 1 million to
give it a chance to continue in some really ugly situation.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
In -RT the spin_lock_irqsave() does not spin but sleep if the lock is
taken. Before that, local_irq_save() is invoked which disables
interrupts even on -RT. Therefore local_irq_save() + spin_lock() does not
work.
In the ->sysrq and oops_in_progress case it is save to trylock the lock
i.e. this is what we do now anyway except for ->sysrq where we assume
that the lock is already taken.
The spin_lock_irqsave() grabs the lock and disables the interrupts on
vanilla (the same behavior) and on -RT it won't disable interrupts.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: add a patch description]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
If the stop machinery is called from inactive CPU we cannot use
lg_global_lock(), because some other stomp machine invocation might be
in progress and the lock can be contended. We cannot schedule from this
context, so use the lovely new lg_global_trylock_relax() primitive to
do what we used to do via one mutex_trylock()/cpu_relax() loop. We
now do that trylock()/relax() across an entire herd of locks. Joy.
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Create lg_global_trylock_relax() for use by stopper thread when it cannot
schedule, to deal with stop_cpus_lock, which is now an lglock.
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Any callers to the function rcu_preempt_qs() must disable irqs in
order to protect the assignment to ->rcu_read_unlock_special. In
RT case, rcu_bh_qs() as the wrapper of rcu_preempt_qs() is called
in some scenarios where irq is enabled, like this path,
do_single_softirq()
|
+ local_irq_enable();
+ handle_softirq()
| |
| + rcu_bh_qs()
| |
| + rcu_preempt_qs()
|
+ local_irq_disable()
So here we'd better disable irq directly inside of rcu_bh_qs() to
fix this, otherwise the kernel may be freezable sometimes as
observed. And especially this way is also kind and safe for the
potential rcu_bh_qs() usage elsewhere in the future.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: Bin Jiang <bin.jiang@windriver.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Implementing RCU-bh in terms of RCU-preempt makes the system vulnerable
to network-based denial-of-service attacks. This patch therefore
makes __do_softirq() invoke rcu_bh_qs(), but only when __do_softirq()
is running in ksoftirqd context. A wrapper layer in interposed so that
other calls to __do_softirq() avoid invoking rcu_bh_qs(). The underlying
function __do_softirq_common() does the actual work.
The reason that rcu_bh_qs() is bad in these non-ksoftirqd contexts is
that there might be a local_bh_enable() inside an RCU-preempt read-side
critical section. This local_bh_enable() can invoke __do_softirq()
directly, so if __do_softirq() were to invoke rcu_bh_qs() (which just
calls rcu_preempt_qs() in the PREEMPT_RT_FULL case), there would be
an illegal RCU-preempt quiescent state in the middle of an RCU-preempt
read-side critical section. Therefore, quiescent states can only happen
in cases where __do_softirq() is invoked directly from ksoftirqd.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20111005184518.GA21601@linux.vnet.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
The Linux kernel has long RCU-bh read-side critical sections that
intolerably increase scheduling latency under mainline's RCU-bh rules,
which include RCU-bh read-side critical sections being non-preemptible.
This patch therefore arranges for RCU-bh to be implemented in terms of
RCU-preempt for CONFIG_PREEMPT_RT_FULL=y.
This has the downside of defeating the purpose of RCU-bh, namely,
handling the case where the system is subjected to a network-based
denial-of-service attack that keeps at least one CPU doing full-time
softirq processing. This issue will be fixed by a later commit.
The current commit will need some work to make it appropriate for
mainline use, for example, it needs to be extended to cover Tiny RCU.
[ paulmck: Added a useful changelog ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20111005185938.GA20403@linux.vnet.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This will void a warning comming from the spin-lock debugging code. The
lock avoiding idea is from Steven Rostedt.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Mike Galbraith captered the following:
| >#11 [ffff88017b243e90] _raw_spin_lock at ffffffff815d2596
| >#12 [ffff88017b243e90] rt_mutex_trylock at ffffffff815d15be
| >#13 [ffff88017b243eb0] get_next_timer_interrupt at ffffffff81063b42
| >#14 [ffff88017b243f00] tick_nohz_stop_sched_tick at ffffffff810bd1fd
| >#15 [ffff88017b243f70] tick_nohz_irq_exit at ffffffff810bd7d2
| >#16 [ffff88017b243f90] irq_exit at ffffffff8105b02d
| >#17 [ffff88017b243fb0] reschedule_interrupt at ffffffff815db3dd
| >--- <IRQ stack> ---
| >#18 [ffff88017a2a9bc8] reschedule_interrupt at ffffffff815db3dd
| > [exception RIP: task_blocks_on_rt_mutex+51]
| >#19 [ffff88017a2a9ce0] rt_spin_lock_slowlock at ffffffff815d183c
| >#20 [ffff88017a2a9da0] lock_timer_base.isra.35 at ffffffff81061cbf
| >#21 [ffff88017a2a9dd0] schedule_timeout at ffffffff815cf1ce
| >#22 [ffff88017a2a9e50] rcu_gp_kthread at ffffffff810f9bbb
| >#23 [ffff88017a2a9ed0] kthread at ffffffff810796d5
| >#24 [ffff88017a2a9f50] ret_from_fork at ffffffff815da04c
lock_timer_base() does a try_lock() which deadlocks on the waiter lock
not the lock itself.
This patch takes the waiter_lock with trylock so it should work from interrupt
context as well. If the fastpath doesn't work and the waiter_lock itself is
taken then it seems that the lock itself taken.
This patch also adds "rt_spin_unlock_after_trylock_in_irq" to keep lockdep
happy. If we managed to take the wait_lock in the first place we should also
be able to take it in the unlock path.
Cc: stable-rt@vger.kernel.org
Reported-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
It was previously discovered that some systems would hang on boot up
with a previous version of 3.12-rt. This was due to RCU using irq_work,
and RT defers the irq_work to a softirq. But if there's no active
timers, the softirq will not be raised, and RCU work will not get done,
causing the system to hang. The fix was to check that if there was no
active timers but irq_work to be done, then we should raise the softirq.
But this fix was not 100% correct. It left out the case that there were
active timers that were not expired yet. This would have the softirq
not get raised even if there was irq work to be done.
If there is irq_work to be done, then we must raise the timer softirq
regardless of if there is active timers or whether they are expired or
not. The softirq can handle those cases. But we can never ignore
irq_work.
As it is only PREEMPT_RT_FULL that requires irq_work to be done in the
softirq, we can pull out the check in the active_timers condition, and
make the code a bit cleaner by having the irq_work check separate, and
put the code in with the other #ifdef PREEMPT_RT. If there is irq_work
to be done, there's no need to check the active timers or if they are
expired. Just raise the time softirq and be done with it. Otherwise, we
can do the timer checks just like we do with non -rt.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ Talking with Sebastian on IRC, it seems that doing the irq_work_run()
from the interrupt in -rt is a bad thing. Here we simply raise the
softirq if there's irq work to do. This too boots on my i7 ]
After trying hard to figure out why my i7 box was locking up with the
new active_timers code, that does not run the timer softirq if there
are no active timers, I took an extra look at the softirq handler and
noticed that it doesn't just run timer softirqs, it also runs irq work.
This was the bug that was locking up the system. It wasn't missing a
timer, it was missing irq work. By always doing the irq work callbacks,
the system boots fine. The missing irq work callback was the RCU's
sp_wakeup() function.
No need to check for defined(CONFIG_IRQ_WORK). When that's not set the
"irq_work_needs_cpu()" is a static inline that returns false.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Mike,
On Thu, 7 Nov 2013, Mike Galbraith wrote:
> On Thu, 2013-11-07 at 04:26 +0100, Mike Galbraith wrote:
> > On Wed, 2013-11-06 at 18:49 +0100, Thomas Gleixner wrote:
>
> > > I bet you are trying to work around some of the side effects of the
> > > occasional tick which is still necessary despite of full nohz, right?
> >
> > Nope, I wanted to check out cost of nohz_full for rt, and found that it
> > doesn't work at all instead, looked, and found that the sole running
> > task has just awakened ksoftirqd when it wants to shut the tick down, so
> > that shutdown never happens.
>
> Like so in virgin 3.10-rt. Box is x3550 M3 booted nowatchdog
> rcu_nocbs=1-3 nohz_full=1-3, and CPUs1-3 are completely isolated via
> cpusets as well.
well, that very same problem is in mainline if you add "threadirqs" to
the command line. But we can be smart about this. The untested patch
below should address that issue. If that works on mainline we can
adapt it for RT (needs a trylock(&base->lock) there).
Though it's not a full solution. It needs some thought versus the
softirq code of timers. Assume we have only one timer queued 1000
ticks into the future. So this change will cause the timer softirq not
to be called until that timer expires and then the timer softirq is
going to do 1000 loops until it catches up with jiffies. That's
anything but pretty ...
What worries me more is this one:
pert-5229 [003] d..h1.. 684.482618: softirq_raise: vec=9 [action=RCU]
The CPU has no callbacks as you shoved them over to cpu 0, so why is
the RCU softirq raised?
Thanks,
tglx
------------------
Message-id: <alpine.DEB.2.02.1311071158350.23353@ionos.tec.linutronix.de>
|CONFIG_NO_HZ_FULL + CONFIG_PREEMPT_RT_FULL = nogo
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
This fixes the following build error for the preempt-rt kernel.
make kernel/fork.o
CC kernel/fork.o
kernel/fork.c:90: error: section of tasklist_lock conflicts with previous declaration
make[2]: *** [kernel/fork.o] Error 1
make[1]: *** [kernel/fork.o] Error 2
The rt kernel cache aligns the RWLOCK in DEFINE_RWLOCK by default.
The non-rt kernels explicitly cache align only the tasklist_lock in
kernel/fork.c
That can create a build conflict. This fixes the build problem by making the
non-rt kernels cache align RWLOCKs by default. The side effect is that
the other RWLOCKs are also cache aligned for non-rt.
This is a short term solution for rt only.
The longer term solution would be to push the cache aligned DEFINE_RWLOCK
to mainline. If there are objections, then we could create a
DEFINE_RWLOCK_CACHE_ALIGNED or something of that nature.
Comments? Objections?
Signed-off-by: John Kacur <jkacur@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/alpine.LFD.2.00.1109191104010.23118@localhost6.localdomain6
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Bad return value in _mutex_lock_check_stamp - this problem only would show
up with 3.12.1 rt4 applied but CONFIG_PREEMPT_RT_FULL not enabled
currently it would be returning what ever vprintk_emit ended up with
(atleast on x86), which probably is not the intended behavior. Added a
return 0; as in the case with CONFIG_PREEMPT_RT_FULL enabled.
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
lockdep says:
| --------------------------------------------------------------------------
| | Wound/wait tests |
| ---------------------
| ww api failures: ok | ok | ok |
| ww contexts mixing: ok | ok |
| finishing ww context: ok | ok | ok | ok |
| locking mismatches: ok | ok | ok |
| EDEADLK handling: ok | ok | ok | ok | ok | ok | ok | ok | ok | ok |
| spinlock nest unlocked: ok |
| -----------------------------------------------------
| |block | try |context|
| -----------------------------------------------------
| context: ok | ok | ok |
| try: ok | ok | ok |
| block: ok | ok | ok |
| spinlock: ok | ok | ok |
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
With the migration pushdonw a few of the do{ }while(0)
loops became obsolete but got left over - this patch
only removes this fallout.
Patch applies on top of 3.12.9-rt13
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
If there's no complaints about it. I'm going to add this to the 3.12-rt
stable tree. As without it, it fails horribly with the cpu hotplug
stress test, and I wont release a stable kernel that does that.
Signed-off-by: Steven Rostedt <rostedt@goodmis.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>
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>
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>
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>
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>
In exit_pi_state_list() we have the following locking construct:
spin_lock(&hb->lock);
raw_spin_lock_irq(&curr->pi_lock);
...
spin_unlock(&hb->lock);
In !RT this works, but on RT the migrate_enable() function which is
called from spin_unlock() sees atomic context due to the held pi_lock
and just decrements the migrate_disable_atomic counter of the
task. Now the next call to migrate_disable() sees the counter being
negative and issues a warning. That check should be in
migrate_enable() already.
Fix this by dropping pi_lock before unlocking hb->lock and reaquire
pi_lock after that again. This is safe as the loop code reevaluates
head again under the pi_lock.
Reported-by: Yong Zhang <yong.zhang@windriver.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Thomas Gleixner
Steven Rostedt
Sebastian Andrzej Siewior
Mike Galbraith
Mike Galbraith
Yong Zhang
Ingo Molnar
Mike Galbraith
Tiejun Chen
Paul E. McKenney
Peter Zijlstra
John Kacur
Nicholas Mc Guire
Sebastian Andrzej Siewior