Linus Torvalds 69cd9eba38 futex: avoid race between requeue and wake ... Jan Stancek reported: "pthread_cond_broadcast/4-1.c testcase from openposix testsuite (LTP) occasionally fails, because some threads fail to wake up. Testcase creates 5 threads, which are all waiting on same condition. Main thread then calls pthread_cond_broadcast() without holding mutex, which calls: futex(uaddr1, FUTEX_CMP_REQUEUE_PRIVATE, 1, 2147483647, uaddr2, ..) This immediately wakes up single thread A, which unlocks mutex and tries to wake up another thread: futex(uaddr2, FUTEX_WAKE_PRIVATE, 1) If thread A manages to call futex_wake() before any waiters are requeued for uaddr2, no other thread is woken up" The ordering constraints for the hash bucket waiter counting are that the waiter counts have to be incremented _before_ getting the spinlock (because the spinlock acts as part of the memory barrier), but the "requeue" operation didn't honor those rules, and nobody had even thought about that case. This fairly simple patch just increments the waiter count for the target hash bucket (hb2) when requeing a futex before taking the locks. It then decrements them again after releasing the lock - the code that actually moves the futex(es) between hash buckets will do the additional required waiter count housekeeping. Reported-and-tested-by: Jan Stancek <jstancek@redhat.com> Acked-by: Davidlohr Bueso <davidlohr@hp.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org # 3.14 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2014-04-09 08:02:12 -07:00
..
debug
events
gcov
irq
locking	lglock: map to spinlock when !CONFIG_SMP	2014-04-07 16:36:14 -07:00
power	kernel: use macros from compiler.h instead of __attribute__((...))	2014-04-07 16:36:11 -07:00
printk
rcu
sched	Merge branch 'akpm' (incoming from Andrew)	2014-04-07 16:38:06 -07:00
time	kernel: use macros from compiler.h instead of __attribute__((...))	2014-04-07 16:36:11 -07:00
trace	Merge branch 'akpm' (incoming from Andrew)	2014-04-07 16:38:06 -07:00
.gitignore
acct.c
async.c
audit.c
audit.h
audit_tree.c
audit_watch.c
auditfilter.c
auditsc.c
backtracetest.c
bounds.c
capability.c
cgroup.c
cgroup_freezer.c
compat.c
configs.c
context_tracking.c
cpu.c
cpu_pm.c
cpuset.c
crash_dump.c
cred.c
delayacct.c
dma.c
elfcore.c
exec_domain.c
exit.c
extable.c
fork.c	kernel: use macros from compiler.h instead of __attribute__((...))	2014-04-07 16:36:11 -07:00
freezer.c
futex.c	futex: avoid race between requeue and wake	2014-04-09 08:02:12 -07:00
futex_compat.c
groups.c
hrtimer.c
hung_task.c
irq_work.c
itimer.c
jump_label.c
kallsyms.c	kernel: use macros from compiler.h instead of __attribute__((...))	2014-04-07 16:36:11 -07:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kexec.c	kernel: use macros from compiler.h instead of __attribute__((...))	2014-04-07 16:36:11 -07:00
kmod.c
kprobes.c
ksysfs.c	kernel: use macros from compiler.h instead of __attribute__((...))	2014-04-07 16:36:11 -07:00
kthread.c
latencytop.c
Makefile
module-internal.h
module.c	modules: use raw_cpu_write for initialization of per cpu refcount.	2014-04-07 16:36:14 -07:00
module_signing.c
notifier.c
nsproxy.c
padata.c
panic.c
params.c
pid.c
pid_namespace.c
posix-cpu-timers.c
posix-timers.c
profile.c
ptrace.c
range.c
reboot.c
relay.c
res_counter.c
resource.c
seccomp.c
signal.c	kernel: use macros from compiler.h instead of __attribute__((...))	2014-04-07 16:36:11 -07:00
smp.c
smpboot.c
smpboot.h
softirq.c
stacktrace.c
stop_machine.c
sys.c
sys_ni.c
sysctl.c
sysctl_binary.c
system_certificates.S
system_keyring.c
task_work.c
taskstats.c
test_kprobes.c
time.c
timeconst.bc
timer.c
torture.c
tracepoint.c
tsacct.c
uid16.c
up.c
user-return-notifier.c
user.c
user_namespace.c
utsname.c
utsname_sysctl.c
watchdog.c
workqueue.c
workqueue_internal.h