Paul E. McKenney aa24f93753 rcu: Fix rcu_barrier_callback() race condition ... The rcu_barrier_callback() function does an atomic_dec_and_test(), and if it is the last CPU to check in, does the required wakeup. Either way, it does an event trace. Unfortunately, this is susceptible to the following sequence of events: o CPU 0 invokes rcu_barrier_callback(), but atomic_dec_and_test() says that it is not last. But at this point, CPU 0 is delayed, perhaps due to an NMI, SMI, or vCPU preemption. o CPU 1 invokes rcu_barrier_callback(), and atomic_dec_and_test() says that it is last. So CPU 1 traces completion and does the needed wakeup. o The awakened rcu_barrier() function does cleanup and releases rcu_state.barrier_mutex. o Another CPU now acquires rcu_state.barrier_mutex and starts another round of rcu_barrier() processing, including updating rcu_state.barrier_sequence. o CPU 0 gets its act back together and does its tracing. Except that rcu_state.barrier_sequence has already been updated, so its tracing is incorrect and probably quite confusing. (Wait! Why did this CPU check in twice for one rcu_barrier() invocation???) This commit therefore causes rcu_barrier_callback() to take a snapshot of the value of rcu_state.barrier_sequence before invoking atomic_dec_and_test(), thus guaranteeing that the event-trace output is sensible, even if the timing of the event-trace output might still be confusing. (Wait! Why did the old rcu_barrier() complete before all of its CPUs checked in???) But being that this is RCU, only so much confusion can reasonably be eliminated. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely and due to the mild consequences of the failure, namely a confusing event trace. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>		2020-02-20 15:58:23 -08:00
..
bpf	Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net	2020-02-08 17:15:08 -08:00
cgroup	Merge branch 'merge.nfs-fs_parse.1' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2020-02-08 13:26:41 -08:00
configs
debug	Revert "kdb: Get rid of confusing diag msg from "rd" if current task has no regs"	2020-02-06 11:40:09 +00:00
dma
events	A set of fixes and improvements for the perf subsystem:	2020-02-09 12:04:09 -08:00
gcov
irq	A set of fixes for X86:	2020-02-09 12:11:12 -08:00
livepatch
locking	locking/rtmutex: rcu: Add WRITE_ONCE() to rt_mutex ->owner	2020-02-20 15:58:22 -08:00
power
printk
rcu	rcu: Fix rcu_barrier_callback() race condition	2020-02-20 15:58:23 -08:00
sched
time	timer: Use hlist_unhashed_lockless() in timer_pending()	2020-02-20 15:58:22 -08:00
trace	Tracing updates:	2020-02-06 07:12:11 +00:00
.gitignore
acct.c
async.c
audit_fsnotify.c
audit_tree.c
audit_watch.c
audit.c
audit.h
auditfilter.c
auditsc.c
backtracetest.c
bounds.c
capability.c
compat.c
configs.c
context_tracking.c
cpu_pm.c
cpu.c
crash_core.c
crash_dump.c
cred.c
delayacct.c
dma.c
elfcore.c
exec_domain.c
exit.c
extable.c
fail_function.c
fork.c
freezer.c
futex.c
gen_kheaders.sh
groups.c
hung_task.c
iomem.c
irq_work.c
jump_label.c
kallsyms.c	Kbuild updates for v5.6 (2nd)	2020-02-09 16:05:50 -08:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kcov.c
kexec_core.c
kexec_elf.c
kexec_file.c
kexec_internal.h
kexec.c
kheaders.c
kmod.c
kprobes.c
ksysfs.c
kthread.c
latencytop.c
Makefile
module_signature.c
module_signing.c
module-internal.h
module.c
notifier.c
nsproxy.c
padata.c
panic.c
params.c
pid_namespace.c
pid.c
profile.c
ptrace.c
range.c
reboot.c
relay.c
resource.c
rseq.c
seccomp.c
signal.c
smp.c
smpboot.c
smpboot.h
softirq.c
stackleak.c
stacktrace.c
stop_machine.c
sys_ni.c
sys.c
sysctl_binary.c
sysctl-test.c
sysctl.c
task_work.c
taskstats.c
test_kprobes.c
torture.c
tracepoint.c
tsacct.c
ucount.c
uid16.c
uid16.h
umh.c
up.c	smp/up: Make smp_call_function_single() match SMP semantics	2020-02-07 15:34:12 +01:00
user_namespace.c
user-return-notifier.c
user.c
utsname_sysctl.c
utsname.c
watchdog_hld.c
watchdog.c
workqueue_internal.h
workqueue.c