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Thomas Gleixner 83e96c604e futex: Remove warn on in return fixup path 
The WARN_ON() in the fixup return path of futex_lock_pi() can
trigger with false positives.

The following scenario happens:
t1 holds the futex and t2 and t3 are blocked on the kernel side rt_mutex.
t1 releases the futex (and the rt_mutex) and assigned t2 to be the next
owner of the futex.

t2 is interrupted and returns w/o acquiring the rt_mutex, before t1 can
release the rtmutex.

t1 releases the rtmutex and t3 becomes the pending owner of the rtmutex.

t2 notices that it is the designated owner (user space variable) and
fails to acquire the rt_mutex via trylock, because it is not allowed to
steal the rt_mutex from t3. Now it looks at the rt_mutex pending owner (t3)
and assigns the futex and the pi_state to it.

During the fixup t4 steals the rtmutex from t3.

t2 returns from the fixup and the owner of the rt_mutex has changed from
t3 to t4.

There is no need to do another round of fixups from t2. The important
part (t2 is not returning as the user space visible owner) is
done. The further fixups are done, before either t3 or t4 return to
user space.

For the user space it is not relevant which task (t3 or t4) is the real
owner, as long as those are both in the kernel, which is guaranteed by
the serialization of the hash bucket lock. Both tasks (which ever returns
first to userspace - t4 because it locked the rt_mutex or t3 due to a signal)
are going through the lock_futex_pi() return path where the ownership is
fixed before the return to user space.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-01 17:45:14 +01:00
..
irq genirq: stackdump after the "Trying to free already-free IRQ" message 2008-01-30 13:33:24 +01:00
power Merge branch 'task_killable' of git://git.kernel.org/pub/scm/linux/kernel/git/willy/misc 2008-02-01 11:45:47 +11:00
time tick-sched: add more debug information 2008-02-01 17:45:14 +01:00
.gitignore
acct.c acct: real_parent ppid 2008-01-07 14:55:37 -08:00
audit_tree.c [PATCH] audit: watching subtrees 2007-10-21 02:37:45 -04:00
audit.c [AUDIT]: Increase skb->truesize in audit_expand 2008-01-31 19:27:08 -08:00
audit.h [PATCH] audit: watching subtrees 2007-10-21 02:37:45 -04:00
auditfilter.c [PATCH] audit: watching subtrees 2007-10-21 02:37:45 -04:00
auditsc.c auditsc: fix kernel-doc param warnings 2007-10-22 19:40:02 -07:00
backtracetest.c x86: add a simple backtrace test module 2008-01-30 13:33:08 +01:00
capability.c
cgroup_debug.c
cgroup.c Improve cgroup printks 2007-11-14 18:45:37 -08:00
compat.c
configs.c
cpu.c cpu-hotplug: replace per-subsystem mutexes with get_online_cpus() 2008-01-25 21:08:02 +01:00
cpuset.c cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus() 2008-01-25 21:08:02 +01:00
delayacct.c
dma.c
exec_domain.c
exit.c exit: Use task_is_* 2007-12-06 17:35:17 -05:00
extable.c module: Don't report discarded init pages as kernel text. 2008-01-29 17:13:18 +11:00
fork.c KVM: Disallow fork() and similar games when using a VM 2008-01-30 17:53:13 +02:00
futex_compat.c [FUTEX] Fix address computation in compat code. 2007-11-09 16:13:08 -08:00
futex.c futex: Remove warn on in return fixup path 2008-02-01 17:45:14 +01:00
hrtimer.c hrtimer: fix hrtimer_init_sleeper() users 2008-02-01 17:45:13 +01:00
itimer.c
kallsyms.c module: make module_address_lookup safe 2008-01-29 17:13:23 +11:00
Kconfig.hz sched: high-res preemption tick 2008-01-25 21:08:29 +01:00
Kconfig.instrumentation Tiny clean-up of OPROFILE/KPROBES configuration 2007-12-06 09:41:12 -08:00
Kconfig.preempt sched: remove the !PREEMPT_BKL code 2008-01-25 21:08:33 +01:00
kexec.c vmcoreinfo: add the array length of "free_list" for filtering free pages 2008-01-08 16:10:36 -08:00
kfifo.c
kmod.c Fix unbalanced helper_lock in kernel/kmod.c 2008-01-17 15:38:59 -08:00
kprobes.c x86: kprobes: add kprobes smoke tests that run on boot 2008-01-30 13:32:53 +01:00
ksysfs.c Kobject: convert remaining kobject_unregister() to kobject_put() 2008-01-24 20:40:40 -08:00
kthread.c sched: fix, always create kernel threads with normal priority 2008-01-25 21:08:33 +01:00
latency.c
latencytop.c sched: latencytop support 2008-01-25 21:08:34 +01:00
lockdep_internals.h
lockdep_proc.c
lockdep.c softlockup: automatically detect hung TASK_UNINTERRUPTIBLE tasks 2008-01-25 21:08:02 +01:00
Makefile x86: add a simple backtrace test module 2008-01-30 13:33:08 +01:00
marker.c Linux Kernel Markers: fix marker mutex not taken upon module load 2007-11-14 18:45:40 -08:00
module.c x86/non-x86: percpu, node ids, apic ids x86.git fixup 2008-01-30 13:33:32 +01:00
mutex-debug.c
mutex-debug.h
mutex.c Add mutex_lock_killable 2007-12-06 17:37:59 -05:00
mutex.h
notifier.c
ns_cgroup.c
nsproxy.c
panic.c debug: add the end-of-trace marker and the module list to 2008-01-30 13:32:50 +01:00
params.c module: fix the module name length in param_sysfs_builtin 2008-01-29 17:13:24 +11:00
pid.c pidns: Place under CONFIG_EXPERIMENTAL 2007-11-14 18:45:43 -08:00
posix-cpu-timers.c sched: rt-watchdog: fix .rlim_max = RLIM_INFINITY 2008-01-25 21:08:32 +01:00
posix-timers.c
printk.c debug: turn ignore_loglevel into an early param 2008-01-31 22:45:23 +01:00
profile.c debug: clean up kernel/profile.c 2008-01-25 21:08:33 +01:00
ptrace.c Merge branch 'task_killable' of git://git.kernel.org/pub/scm/linux/kernel/git/willy/misc 2008-02-01 11:45:47 +11:00
rcuclassic.c Preempt-RCU: implementation 2008-01-25 21:08:24 +01:00
rcupdate.c Preempt-RCU: fix rcu_barrier for preemptive environment. 2008-01-25 21:08:24 +01:00
rcupreempt_trace.c Preempt-RCU: implementation 2008-01-25 21:08:24 +01:00
rcupreempt.c Preempt-RCU: CPU Hotplug handling 2008-01-25 21:08:25 +01:00
rcutorture.c cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus() 2008-01-25 21:08:02 +01:00
relay.c
resource.c Add IORESOUCE_BUSY flag for System RAM 2007-11-14 18:45:39 -08:00
rtmutex_common.h
rtmutex-debug.c
rtmutex-debug.h
rtmutex-tester.c Driver core: change sysdev classes to use dynamic kobject names 2008-01-24 20:40:40 -08:00
rtmutex.c
rtmutex.h
rwsem.c sched: mark rwsem functions as __sched for wchan/profiling 2007-12-18 15:21:13 +01:00
sched_debug.c sched: keep total / count stats in addition to the max for 2008-01-25 21:08:35 +01:00
sched_fair.c sched: let +nice tasks have smaller impact 2008-01-31 22:45:22 +01:00
sched_idletask.c sched: high-res preemption tick 2008-01-25 21:08:29 +01:00
sched_rt.c sched: fix goto retry in pick_next_task_rt() 2008-01-25 21:08:34 +01:00
sched_stats.h sched: clean up kernel/sched_stat.h 2007-11-28 15:52:56 +01:00
sched.c Merge branch 'task_killable' of git://git.kernel.org/pub/scm/linux/kernel/git/willy/misc 2008-02-01 11:45:47 +11:00
seccomp.c
signal.c Ensure that we export __fatal_signal_pending() 2008-02-01 12:58:14 +11:00
softirq.c time: track accurate idle time with tick_sched.idle_sleeptime 2008-01-30 13:30:04 +01:00
softlockup.c softlockup: fix signedness 2008-01-25 21:08:34 +01:00
spinlock.c spinlock: lockbreak cleanup 2008-01-30 13:31:20 +01:00
srcu.c
stacktrace.c
stop_machine.c cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus() 2008-01-25 21:08:02 +01:00
sys_ni.c [POWERPC] Provide a way to protect 4k subpages when using 64k pages 2008-01-24 10:06:01 +11:00
sys.c x86: ignore the sys_getcpu() tcache parameter 2007-11-17 16:27:00 +01:00
sysctl_check.c sysctl: Infrastructure for per namespace sysctls 2008-01-28 14:55:17 -08:00
sysctl.c x86: various changes and cleanups to in_p/out_p delay details 2008-01-30 13:30:05 +01:00
taskstats.c kernel/taskstats.c: fix bogus nlmsg_free() 2007-11-14 18:45:44 -08:00
test_kprobes.c x86: kprobes: add kprobes smoke tests that run on boot 2008-01-30 13:32:53 +01:00
time.c timekeeping: update xtime_cache when time(zone) changes 2008-02-01 17:45:13 +01:00
timer.c Merge branch 'task_killable' of git://git.kernel.org/pub/scm/linux/kernel/git/willy/misc 2008-02-01 11:45:47 +11:00
tsacct.c
uid16.c
user_namespace.c
user.c uids: merge multiple error paths in alloc_uid() into one 2008-01-25 21:08:26 +01:00
utsname_sysctl.c Isolate the UTS namespace's domainname and hostname back 2007-11-29 09:24:53 -08:00
utsname.c
wait.c wait: Use TASK_NORMAL 2007-12-06 17:34:36 -05:00
workqueue.c cpu-hotplug: replace per-subsystem mutexes with get_online_cpus() 2008-01-25 21:08:02 +01:00