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Steven Rostedt d473750b40 sched/cpupri: Fix memory barriers for vec updates to always be in order 
[ This patch actually compiles. Thanks to Mike Galbraith for pointing
that out. I compiled and booted this patch with no issues. ]

Re-examining the cpupri patch, I see there's a possible race because the
update of the two priorities vec->counts are not protected by a memory
barrier.

When a RT runqueue is overloaded and wants to push an RT task to another
runqueue, it scans the RT priority vectors in a loop from lowest
priority to highest.

When we queue or dequeue an RT task that changes a runqueue's highest
priority task, we update the vectors to show that a runqueue is rated at
a different priority. To do this, we first set the new priority mask,
and increment the vec->count, and then set the old priority mask by
decrementing the vec->count.

If we are lowering the runqueue's RT priority rating, it will trigger a
RT pull, and we do not care if we miss pushing to this runqueue or not.

But if we raise the priority, but the priority is still lower than an RT
task that is looking to be pushed, we must make sure that this runqueue
is still seen by the push algorithm (the loop).

Because the loop reads from lowest to highest, and the new priority is
set before the old one is cleared, we will either see the new or old
priority set and the vector will be checked.

But! Since there's no memory barrier between the updates of the two, the
old count may be decremented first before the new count is incremented.
This means the loop may see the old count of zero and skip it, and also
the new count of zero before it was updated. A possible runqueue that
the RT task could move to could be missed.

A conditional memory barrier is placed between the vec->count updates
and is only called when both updates are done.

The smp_wmb() has also been changed to smp_mb__before_atomic_inc/dec(),
as they are not needed by archs that already synchronize
atomic_inc/dec().

The smp_rmb() has been moved to be called at every iteration of the loop
so that the race between seeing the two updates is visible by each
iteration of the loop, as an arch is free to optimize the reading of
memory of the counters in the loop.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1312547269.18583.194.camel@gandalf.stny.rr.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-08-14 12:01:07 +02:00
..
debug Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/linux-2.6-kgdb 2011-08-01 13:39:40 -10:00
events perf: Remove perf_event_attr::type check 2011-07-21 20:41:55 +02:00
gcov gcov: disable CONSTRUCTORS for UML 2011-07-26 16:49:45 -07:00
irq Merge branch 'imx/dt' into next/dt 2011-07-28 15:25:46 +00:00
power Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-07-25 13:56:39 -07:00
time Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-07-22 16:52:18 -07:00
trace Merge branch 'linus' into perf/urgent 2011-08-05 10:33:55 +02:00
.gitignore
acct.c
async.c async: Fixed an include coding style issue 2011-06-14 22:48:46 -04:00
audit_tree.c audit_tree,rcu: Convert call_rcu(__put_tree) to kfree_rcu() 2011-07-20 14:10:11 -07:00
audit_watch.c kill path_lookup() 2011-03-14 09:15:23 -04:00
audit.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
audit.h
auditfilter.c netlink: kill loginuid/sessionid/sid members from struct netlink_skb_parms 2011-03-03 10:55:40 -08:00
auditsc.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
backtracetest.c
bounds.c memcg: remove direct page_cgroup-to-page pointer 2011-03-23 19:46:28 -07:00
capability.c Merge branch 'master' into next 2011-05-19 18:51:57 +10:00
cgroup_freezer.c cgroups: add per-thread subsystem callbacks 2011-05-26 17:12:34 -07:00
cgroup.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6 2011-07-27 19:26:38 -07:00
compat.c Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-2.6 2011-07-30 00:08:53 -07:00
configs.c kernel/configs.c: include MODULE_*() when CONFIG_IKCONFIG_PROC=n 2011-07-25 20:57:15 -07:00
cpu.c Fix common misspellings 2011-03-31 11:26:23 -03:00
cpuset.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
crash_dump.c crash_dump: export is_kdump_kernel to modules, consolidate elfcorehdr_addr, setup_elfcorehdr and saved_max_pfn 2011-03-23 19:47:19 -07:00
cred.c move RLIMIT_NPROC check from set_user() to do_execve_common() 2011-08-11 11:24:42 -07:00
delayacct.c KVM: Steal time implementation 2011-07-14 12:59:14 +03:00
dma.c
elfcore.c
exec_domain.c
exit.c ipc: introduce shm_rmid_forced sysctl 2011-07-26 16:49:44 -07:00
extable.c extable, core_kernel_data(): Make sure all archs define _sdata 2011-05-20 08:56:56 +02:00
fork.c move RLIMIT_NPROC check from set_user() to do_execve_common() 2011-08-11 11:24:42 -07:00
freezer.c Freezer: Use SMP barriers 2011-05-17 23:19:17 +02:00
futex_compat.c userns: user namespaces: convert several capable() calls 2011-03-23 19:47:08 -07:00
futex.c Merge branch 'linus' into core/urgent 2011-08-04 09:09:27 +02:00
groups.c userns: user namespaces: convert several capable() calls 2011-03-23 19:47:08 -07:00
hrtimer.c hrtimers: Fix typo causing erratic timers 2011-05-25 15:31:58 -07:00
hung_task.c watchdog, hung_task_timeout: Add Kconfig configurable default 2011-04-28 09:13:17 +02:00
irq_work.c irq_work: Use per cpu atomics instead of regular atomics 2010-12-18 15:54:48 +01:00
itimer.c
jump_label.c jump_label: Fix jump_label update for modules 2011-06-29 09:59:17 -04:00
kallsyms.c Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-03-25 17:52:22 -07:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks arch:Kconfig.locks Remove unused config option. 2011-04-10 17:01:05 +02:00
Kconfig.preempt sched: Isolate preempt counting in its own config option 2011-06-10 15:15:40 +02:00
kexec.c treewide: Convert uses of struct resource to resource_size(ptr) 2011-06-10 14:55:36 +02:00
kfifo.c
kmod.c Boot up with usermodehelper disabled 2011-08-03 22:03:29 -10:00
kprobes.c kprobes: Return -ENOENT if probe point doesn't exist 2011-07-15 15:11:47 -04:00
ksysfs.c kernel/ksysfs.c: expose file_caps_enabled in sysfs 2011-04-19 16:45:51 -07:00
kthread.c cpuset: Fix cpuset_cpus_allowed_fallback(), don't update tsk->rt.nr_cpus_allowed 2011-05-28 17:02:57 +02:00
latencytop.c Fix common misspellings 2011-03-31 11:26:23 -03:00
lockdep_internals.h
lockdep_proc.c lockdep: Remove unused 'factor' variable from lockdep_stats_show() 2011-03-23 13:54:47 +01:00
lockdep_states.h
lockdep.c lockdep: Clear whole lockdep_map on initialization 2011-08-04 10:17:56 +02:00
Makefile jump label: Reduce the cycle count by changing the link order 2011-08-05 23:57:33 +02:00
module.c module: add /sys/module/<name>/uevent files 2011-07-24 22:06:04 +09:30
mutex-debug.c mutex: Use p->on_cpu for the adaptive spin 2011-04-14 08:52:33 +02:00
mutex-debug.h mutex: Use p->on_cpu for the adaptive spin 2011-04-14 08:52:33 +02:00
mutex.c lockdep, mutex: provide mutex_lock_nest_lock 2011-05-25 08:39:17 -07:00
mutex.h mutex: Use p->on_cpu for the adaptive spin 2011-04-14 08:52:33 +02:00
notifier.c notifiers: sys: move reboot notifiers into reboot.h 2011-07-25 20:57:14 -07:00
nsproxy.c make sure that nsproxy_cache is initialized early enough 2011-07-20 01:44:07 -04:00
padata.c Fix common misspellings 2011-03-31 11:26:23 -03:00
panic.c panic: panic=-1 for immediate reboot 2011-07-26 16:49:45 -07:00
params.c module: add /sys/module/<name>/uevent files 2011-07-24 22:06:04 +09:30
pid_namespace.c pidns: call pid_ns_prepare_proc() from create_pid_namespace() 2011-03-23 19:46:58 -07:00
pid.c rcu: treewide: Do not use rcu_read_lock_held when calling rcu_dereference_check 2011-07-08 22:21:58 +02:00
pm_qos_params.c plist: Remove the need to supply locks to plist heads 2011-07-08 14:02:53 +02:00
posix-cpu-timers.c hrtimers: Avoid touching inactive timer bases 2011-05-23 13:59:54 +02:00
posix-timers.c posix-timers: RCU conversion 2011-05-24 12:10:51 +02:00
printk.c cap_syslog: don't use WARN_ONCE for CAP_SYS_ADMIN deprecation warning 2011-08-09 18:22:22 -07:00
profile.c kernel/profile.c: remove some duplicate code from profile_hits() 2011-05-26 17:12:37 -07:00
ptrace.c connector: add an event for monitoring process tracers 2011-07-18 21:38:33 +02:00
range.c
rcupdate.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
rcutiny_plugin.h rcu: Converge TINY_RCU expedited and normal boosting 2011-05-05 23:16:58 -07:00
rcutiny.c sanitize <linux/prefetch.h> usage 2011-05-20 12:50:29 -07:00
rcutorture.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
rcutree_plugin.h softirq,rcu: Inform RCU of irq_exit() activity 2011-07-20 10:50:12 -07:00
rcutree_trace.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
rcutree.c rcu: Prevent RCU callbacks from executing before scheduler initialized 2011-07-13 08:17:56 -07:00
rcutree.h rcu: Move RCU_BOOST #ifdefs to header file 2011-06-16 16:12:05 -07:00
relay.c
res_counter.c memcg: res_counter_read_u64(): fix potential races on 32-bit machines 2011-03-23 19:46:22 -07:00
resource.c resources: Add lookup_resource() 2011-07-30 21:21:39 +02:00
rtmutex_common.h rtmutex: Simplify PI algorithm and make highest prio task get lock 2011-01-27 21:13:51 -05:00
rtmutex-debug.c rtmutex: Simplify PI algorithm and make highest prio task get lock 2011-01-27 21:13:51 -05:00
rtmutex-debug.h
rtmutex-tester.c rtmutex: tester: Remove the remaining BKL leftovers 2011-02-22 22:07:22 +01:00
rtmutex.c plist: Remove the need to supply locks to plist heads 2011-07-08 14:02:53 +02:00
rtmutex.h
rwsem.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
sched_autogroup.c Fix common misspellings 2011-03-31 11:26:23 -03:00
sched_autogroup.h sched: Skip autogroup when looking for all rt sched groups 2011-07-01 10:39:08 +02:00
sched_clock.c
sched_cpupri.c sched/cpupri: Fix memory barriers for vec updates to always be in order 2011-08-14 12:01:07 +02:00
sched_cpupri.h sched/cpupri: Remove the vec->lock 2011-08-14 12:01:03 +02:00
sched_debug.c sched: Get rid of lock_depth 2011-04-24 13:18:38 +02:00
sched_fair.c sched: Remove noop in lowest_flag_domain() 2011-08-14 12:00:46 +02:00
sched_features.h sched: Kill WAKEUP_PREEMPT 2011-08-14 12:00:41 +02:00
sched_idletask.c sched: Drop the rq argument to sched_class::select_task_rq() 2011-04-14 08:52:36 +02:00
sched_rt.c sched: Use pushable_tasks to determine next highest prio 2011-08-14 12:00:55 +02:00
sched_stats.h sched: More sched_domain iterations fixes 2011-05-28 17:02:54 +02:00
sched_stoptask.c sched: Drop the rq argument to sched_class::select_task_rq() 2011-04-14 08:52:36 +02:00
sched.c sched: fix broken SCHED_RESET_ON_FORK handling 2011-08-14 12:00:43 +02:00
seccomp.c
semaphore.c
signal.c signals: sys_ssetmask/sys_rt_sigsuspend should use set_current_blocked() 2011-07-27 12:53:36 -07:00
smp.c generic-ipi: Fix kexec boot crash by initializing call_single_queue before enabling interrupts 2011-06-17 10:17:12 +02:00
softirq.c softirq,rcu: Inform RCU of irq_exit() activity 2011-07-20 10:50:12 -07:00
spinlock.c
srcu.c rcu: demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status 2011-01-14 04:56:49 -08:00
stacktrace.c stack_trace: Add weak save_stack_trace_regs() 2011-06-14 22:48:52 -04:00
stop_machine.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
sys_ni.c ipc: Add missing sys_ni entries for ipc/compat.c functions 2011-05-20 13:53:02 -07:00
sys.c move RLIMIT_NPROC check from set_user() to do_execve_common() 2011-08-11 11:24:42 -07:00
sysctl_binary.c open-style analog of vfs_path_lookup() 2011-03-14 09:15:28 -04:00
sysctl_check.c sysctl_check: drop dead code 2011-03-23 19:46:51 -07:00
sysctl.c sysctl,rcu: Convert call_rcu(free_head) to kfree 2011-07-20 14:10:18 -07:00
taskstats.c taskstats: add_del_listener() should ignore !valid listeners 2011-08-03 14:25:20 -10:00
test_kprobes.c
time.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-03-15 18:53:35 -07:00
timeconst.pl
timer.c timers: Consider slack value in mod_timer() 2011-06-03 15:02:32 +02:00
tracepoint.c jump label: Introduce static_branch() interface 2011-04-04 12:48:08 -04:00
tsacct.c
uid16.c userns: user namespaces: convert several capable() calls 2011-03-23 19:47:08 -07:00
up.c
user_namespace.c user_ns: improve the user_ns on-the-slab packaging 2011-01-13 08:03:18 -08:00
user-return-notifier.c Fix common misspellings 2011-03-31 11:26:23 -03:00
user.c userns: add a user_namespace as creator/owner of uts_namespace 2011-03-23 19:46:59 -07:00
utsname_sysctl.c
utsname.c ns proc: Add support for the uts namespace 2011-05-10 14:35:35 -07:00
wait.c Fix common misspellings 2011-03-31 11:26:23 -03:00
watchdog.c perf, x86: P4 PMU - Introduce event alias feature 2011-07-14 17:25:04 -04:00
workqueue_sched.h
workqueue.c Merge branch 'for-3.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2011-07-22 15:07:15 -07:00