Frederic Weisbecker 37d9fd3134 rcu/nocb: Remove buggy bypass lock contention mitigation ... [ Upstream commit e4f7805729 ] The bypass lock contention mitigation assumes there can be at most 2 contenders on the bypass lock, following this scheme: 1) One kthread takes the bypass lock 2) Another one spins on it and increment the contended counter 3) A third one (a bypass enqueuer) sees the contended counter on and busy loops waiting on it to decrement. However this assumption is wrong. There can be only one CPU to find the lock contended because call_rcu() (the bypass enqueuer) is the only bypass lock acquire site that may not already hold the NOCB lock beforehand, all the other sites must first contend on the NOCB lock. Therefore step 2) is impossible. The other problem is that the mitigation assumes that contenders all belong to the same rdp CPU, which is also impossible for a raw spinlock. In theory the warning could trigger if the enqueuer holds the bypass lock and another CPU flushes the bypass queue concurrently but this is prevented from all flush users: 1) NOCB kthreads only flush if they successfully _tried_ to lock the bypass lock. So no contention management here. 2) Flush on callbacks migration happen remotely when the CPU is offline. No concurrency against bypass enqueue. 3) Flush on deoffloading happen either locally with IRQs disabled or remotely when the CPU is not yet online. No concurrency against bypass enqueue. 4) Flush on barrier entrain happen either locally with IRQs disabled or remotely when the CPU is offline. No concurrency against bypass enqueue. For those reasons, the bypass lock contention mitigation isn't needed and is even wrong. Remove it but keep the warning reporting a contended bypass lock on a remote CPU, to keep unexpected contention awareness. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		2024-09-08 07:54:44 +02:00
..
bpf	bpf: Fix a kernel verifier crash in stacksafe()	2024-08-29 17:33:58 +02:00
cgroup	cgroup: Avoid extra dereference in css_populate_dir()	2024-08-29 17:33:24 +02:00
configs	Kbuild updates for v6.6	2023-09-05 11:01:47 -07:00
debug	kdb: Use the passed prompt in kdb_position_cursor()	2024-08-03 08:54:34 +02:00
dma	dma-debug: avoid deadlock between dma debug vs printk and netconsole	2024-09-08 07:54:32 +02:00
entry	entry: Respect changes to system call number by trace_sys_enter()	2024-04-03 15:28:50 +02:00
events	bpf, events: Use prog to emit ksymbol event for main program	2024-08-03 08:54:36 +02:00
futex	futex: Don't include process MM in futex key on no-MMU	2023-11-20 11:58:53 +01:00
gcov	gcov: add support for GCC 14	2024-06-27 13:49:13 +02:00
irq	genirq/cpuhotplug: Retry with cpu_online_mask when migration fails	2024-08-19 06:04:24 +02:00
kcsan	kcsan: Don't expect 64 bits atomic builtins from 32 bits architectures	2023-06-09 23:29:50 +10:00
livepatch	livepatch: Fix missing newline character in klp_resolve_symbols()	2023-11-20 11:59:25 +01:00
locking	locking/rwsem: Add __always_inline annotation to __down_write_common() and inlined callers	2024-08-03 08:53:42 +02:00
module	module: make waiting for a concurrent module loader interruptible	2024-08-14 13:58:53 +02:00
power	PM: s2idle: Make sure CPUs will wakeup directly on resume	2024-04-17 11:19:26 +02:00
printk	printk: For @suppress_panic_printk check for other CPU in panic	2024-04-13 13:07:29 +02:00
rcu	rcu/nocb: Remove buggy bypass lock contention mitigation	2024-09-08 07:54:44 +02:00
sched	sched/topology: Handle NUMA_NO_NODE in sched_numa_find_nth_cpu()	2024-08-29 17:33:24 +02:00
time	hrtimer: Prevent queuing of hrtimer without a function callback	2024-08-29 17:33:41 +02:00
trace	tracing: Have format file honor EVENT_FILE_FL_FREED	2024-09-04 13:28:22 +02:00
.gitignore
acct.c	audit/stable-6.6 PR 20230829	2023-08-30 08:17:35 -07:00
async.c	async: Introduce async_schedule_dev_nocall()	2024-01-31 16:18:49 -08:00
audit_fsnotify.c
audit_tree.c
audit_watch.c	audit: don't WARN_ON_ONCE(!current->mm) in audit_exe_compare()	2023-11-28 17:19:56 +00:00
audit.c	audit: Send netlink ACK before setting connection in auditd_set	2024-02-05 20:14:14 +00:00
audit.h	audit: correct audit_filter_inodes() definition	2023-07-21 12:17:25 -04:00
auditfilter.c	ima: Avoid blocking in RCU read-side critical section	2024-07-11 12:49:18 +02:00
auditsc.c	audit,io_uring: io_uring openat triggers audit reference count underflow	2023-10-13 18:34:46 +02:00
backtracetest.c
bounds.c	bounds: Use the right number of bits for power-of-two CONFIG_NR_CPUS	2024-05-02 16:32:50 +02:00
capability.c	lsm: constify the 'target' parameter in security_capget()	2023-08-08 16:48:47 -04:00
cfi.c
compat.c
configs.c
context_tracking.c	locking/atomic: treewide: use raw_atomic*_<op>()	2023-06-05 09:57:20 +02:00
cpu_pm.c
cpu.c	cpu/SMT: Enable SMT only if a core is online	2024-08-29 17:33:30 +02:00
crash_core.c	mm: turn folio_test_hugetlb into a PageType	2024-05-02 16:32:47 +02:00
crash_dump.c
cred.c	cred: get rid of CONFIG_DEBUG_CREDENTIALS	2023-12-20 17:01:51 +01:00
delayacct.c
dma.c
exec_domain.c
exit.c	mm: optimize the redundant loop of mm_update_owner_next()	2024-07-11 12:49:15 +02:00
extable.c
fail_function.c
fork.c	Revert "fork: defer linking file vma until vma is fully initialized"	2024-06-21 14:38:47 +02:00
freezer.c
gen_kheaders.sh	kheaders: explicitly define file modes for archived headers	2024-06-21 14:38:40 +02:00
groups.c
hung_task.c
iomem.c	kernel/iomem.c: remove __weak ioremap_cache helper	2023-08-21 13:37:28 -07:00
irq_work.c
jump_label.c	jump_label: Fix the fix, brown paper bags galore	2024-08-14 13:58:38 +02:00
kallsyms_internal.h
kallsyms_selftest.c	Modules changes for v6.6-rc1	2023-08-29 17:32:32 -07:00
kallsyms_selftest.h
kallsyms.c	kallsyms: Change func signature for cleanup_symbol_name()	2023-08-25 15:00:36 -07:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.kexec	kexec: select CRYPTO from KEXEC_FILE instead of depending on it	2024-01-05 15:19:41 +01:00
Kconfig.locks
Kconfig.preempt
kcov.c	kcov: properly check for softirq context	2024-08-14 13:58:57 +02:00
kexec_core.c	kexec: do syscore_shutdown() in kernel_kexec	2024-01-31 16:18:56 -08:00
kexec_elf.c
kexec_file.c	integrity-v6.6	2023-08-30 09:16:56 -07:00
kexec_internal.h
kexec.c	kernel: kexec: copy user-array safely	2023-11-28 17:19:40 +00:00
kheaders.c
kprobes.c	kprobes: Fix to check symbol prefixes correctly	2024-08-14 13:58:51 +02:00
ksyms_common.c	kallsyms: make kallsyms_show_value() as generic function	2023-06-08 12:27:20 -07:00
ksysfs.c	crash: hotplug support for kexec_load()	2023-08-24 16:25:14 -07:00
kthread.c	kthread: add kthread_stop_put	2024-06-12 11:12:52 +02:00
latencytop.c
Makefile	kernel/numa.c: Move logging out of numa.h	2024-06-12 11:11:50 +02:00
module_signature.c
notifier.c
nsproxy.c	nsproxy: Convert nsproxy.count to refcount_t	2023-08-21 11:29:12 -07:00
numa.c	kernel/numa.c: Move logging out of numa.h	2024-06-12 11:11:50 +02:00
padata.c	padata: Fix possible divide-by-0 panic in padata_mt_helper()	2024-08-14 13:58:59 +02:00
panic.c	panic: Flush kernel log buffer at the end	2024-04-13 13:07:29 +02:00
params.c	kernel: params: Remove unnecessary ‘0’ values from err	2023-07-10 12:47:01 -07:00
pid_namespace.c	zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING	2024-06-21 14:38:50 +02:00
pid_sysctl.h	memfd: replace ratcheting feature from vm.memfd_noexec with hierarchy	2023-08-21 13:37:59 -07:00
pid.c	pidfd: prevent a kernel-doc warning	2023-09-19 13:21:33 -07:00
profile.c	profiling: remove profile=sleep support	2024-08-14 13:58:47 +02:00
ptrace.c
range.c
reboot.c	kernel/reboot: emergency_restart: Set correct system_state	2023-11-28 17:20:04 +00:00
regset.c
relay.c	kernel: relay: remove unnecessary NULL values from relay_open_buf	2023-08-18 10:18:55 -07:00
resource_kunit.c
resource.c	kernel/resource: Increment by align value in get_free_mem_region()	2024-01-10 17:16:58 +01:00
rseq.c
scftorture.c	scftorture: Pause testing after memory-allocation failure	2023-07-14 15:02:57 -07:00
scs.c
seccomp.c	seccomp: Add missing kerndoc notations	2023-08-17 12:32:15 -07:00
signal.c	kernel: rerun task_work while freezing in get_signal()	2024-08-03 08:54:13 +02:00
smp.c	smp,csd: Throw an error if a CSD lock is stuck for too long	2023-11-28 17:19:36 +00:00
smpboot.c	kthread: add kthread_stop_put	2024-06-12 11:12:52 +02:00
smpboot.h
softirq.c	softirq: Fix suspicious RCU usage in __do_softirq()	2024-06-12 11:11:27 +02:00
stackleak.c
stacktrace.c
static_call_inline.c
static_call.c
stop_machine.c
sys_ni.c	syscalls: fix compat_sys_io_pgetevents_time64 usage	2024-07-05 09:34:04 +02:00
sys.c	prctl: generalize PR_SET_MDWE support check to be per-arch	2024-04-03 15:28:54 +02:00
sysctl-test.c
sysctl.c	v6.5-rc1-sysctl-next	2023-06-28 16:05:21 -07:00
task_work.c	task_work: Introduce task_work_cancel() again	2024-08-03 08:54:16 +02:00
taskstats.c
torture.c	rcutorture: Fix stuttering races and other issues	2023-11-28 17:20:08 +00:00
tracepoint.c
tsacct.c
ucount.c	sysctl: Add size to register_sysctl	2023-08-15 15:26:17 -07:00
uid16.c
uid16.h
umh.c	sysctl: fix unused proc_cap_handler() function warning	2023-06-29 15:19:43 -07:00
up.c
user_namespace.c
user-return-notifier.c
user.c
usermode_driver.c
utsname_sysctl.c
utsname.c
vhost_task.c	vhost_task: Handle SIGKILL by flushing work and exiting	2024-07-11 12:49:10 +02:00
watch_queue.c	kernel: watch_queue: copy user-array safely	2023-11-28 17:19:40 +00:00
watchdog_buddy.c	watchdog/hardlockup: move SMP barriers from common code to buddy code	2023-06-19 16:25:28 -07:00
watchdog_perf.c	watchdog/perf: properly initialize the turbo mode timestamp and rearm counter	2024-08-03 08:54:29 +02:00
watchdog.c	watchdog: move softlockup_panic back to early_param	2023-11-28 17:19:57 +00:00
workqueue_internal.h	workqueue: Drop the special locking rule for worker->flags and worker_pool->flags	2023-08-07 15:57:22 -10:00
workqueue.c	workqueue: Fix selection of wake_cpu in kick_pool()	2024-05-17 12:02:31 +02:00