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Will Deacon c61da58d8a locking/qspinlock: Kill cmpxchg() loop when claiming lock from head of queue 
When a queued locker reaches the head of the queue, it claims the lock
by setting _Q_LOCKED_VAL in the lockword. If there isn't contention, it
must also clear the tail as part of this operation so that subsequent
lockers can avoid taking the slowpath altogether.

Currently this is expressed as a cmpxchg() loop that practically only
runs up to two iterations. This is confusing to the reader and unhelpful
to the compiler. Rewrite the cmpxchg() loop without the loop, so that a
failed cmpxchg() implies that there is contention and we just need to
write to _Q_LOCKED_VAL without considering the rest of the lockword.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-7-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:48 +02:00
..
bpf bpf: sockmap remove dead check 2018-04-20 22:09:51 +02:00
cgroup Merge branch 'for-4.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2018-04-03 18:00:13 -07:00
configs KVM changes for 4.16 2018-02-10 13:16:35 -08:00
debug * Fix 2032 time access issues and new compiler warnings 2018-04-12 10:21:19 -07:00
events perf: Remove superfluous allocation error check 2018-04-17 09:47:40 -03:00
gcov License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
irq genirq/affinity: Spread irq vectors among present CPUs as far as possible 2018-04-06 12:19:51 +02:00
livepatch livepatch: Allow to call a custom callback when freeing shadow variables 2018-04-17 13:42:48 +02:00
locking locking/qspinlock: Kill cmpxchg() loop when claiming lock from head of queue 2018-04-27 09:48:48 +02:00
power PM / QoS: mark expected switch fall-throughs 2018-04-09 13:49:40 +02:00
printk New features: 2018-04-10 11:27:30 -07:00
rcu Merge branches 'fixes.2018.02.23a', 'srcu.2018.02.20a' and 'torture.2018.02.20a' into HEAD 2018-02-23 15:15:41 -08:00
sched Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-04-15 12:43:30 -07:00
time posix-cpu-timers: Ensure set_process_cpu_timer is always evaluated 2018-04-19 12:54:57 +02:00
trace Following tracing fixes: 2018-04-26 16:22:47 -07:00
.gitignore
acct.c kernel/acct.c: fix the acct->needcheck check in check_free_space() 2018-01-04 16:45:09 -08:00
async.c kernel/async.c: revert "async: simplify lowest_in_progress()" 2018-02-06 18:32:44 -08:00
audit.c audit/stable-4.17 PR 20180403 2018-04-06 15:01:25 -07:00
audit.h audit: track the owner of the command mutex ourselves 2018-02-23 11:22:22 -05:00
audit_fsnotify.c
audit_tree.c audit: track the owner of the command mutex ourselves 2018-02-23 11:22:22 -05:00
audit_watch.c
auditfilter.c audit: deprecate the AUDIT_FILTER_ENTRY filter 2018-02-15 14:36:29 -05:00
auditsc.c audit: bail before bug check if audit disabled 2018-02-15 14:40:25 -05:00
backtracetest.c
bounds.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
capability.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
compat.c mm: add kernel_move_pages() helper, move compat syscall to mm/migrate.c 2018-04-02 20:15:32 +02:00
configs.c
context_tracking.c
cpu.c cpu/hotplug: Fix unused function warning 2018-03-15 20:34:40 +01:00
cpu_pm.c
crash_core.c kexec: export PG_swapbacked to VMCOREINFO 2018-04-13 17:10:27 -07:00
crash_dump.c
cred.c
delayacct.c delayacct: Account blkio completion on the correct task 2018-01-16 03:29:36 +01:00
dma.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
elfcore.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
exec_domain.c get rid of pointless includes of fs_struct.h 2018-02-22 14:28:50 -05:00
exit.c kernel: use kernel_wait4() instead of sys_wait4() 2018-04-02 20:14:51 +02:00
extable.c extable: Make init_kernel_text() global 2018-02-21 16:54:06 +01:00
fail_function.c error-injection: Fix to prohibit jump optimization 2018-03-12 16:16:00 +01:00
fork.c fork: unconditionally clear stack on fork 2018-04-20 17:18:35 -07:00
freezer.c
futex.c pids: introduce find_get_task_by_vpid() helper 2018-02-06 18:32:46 -08:00
futex_compat.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
groups.c kernel: make groups_sort calling a responsibility group_info allocators 2017-12-14 16:00:49 -08:00
hung_task.c
irq_work.c irq/work: Improve the flag definitions 2018-01-08 19:43:15 +01:00
jump_label.c jump_label: Disable jump labels in __exit code 2018-03-20 08:57:17 +01:00
kallsyms.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk 2018-02-01 13:36:15 -08:00
kcmp.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kcov.c kcov: detect double association with a single task 2018-02-06 18:32:46 -08:00
kexec.c kexec: call do_kexec_load() in compat syscall directly 2018-04-02 20:15:01 +02:00
kexec_core.c
kexec_file.c kernel/kexec_file.c: allow archs to set purgatory load address 2018-04-13 17:10:28 -07:00
kexec_internal.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kmod.c
kprobes.c kprobes: Fix random address output of blacklist file 2018-04-25 10:27:56 -04:00
ksysfs.c
kthread.c treewide: Remove TIMER_FUNC_TYPE and TIMER_DATA_TYPE casts 2017-11-21 16:35:54 -08:00
latencytop.c
Makefile error-injection: Support fault injection framework 2018-01-12 17:33:38 -08:00
memremap.c kernel/memremap: Remove stale devres_free() call 2018-03-06 10:58:54 -08:00
module-internal.h
module.c arch: remove obsolete architecture ports 2018-04-02 20:20:12 -07:00
module_signing.c
notifier.c
nsproxy.c
padata.c padata: add SPDX identifier 2018-01-05 18:43:00 +11:00
panic.c taint: add taint for randstruct 2018-04-11 10:28:35 -07:00
params.c kernel/params.c: downgrade warning for unsafe parameters 2018-04-11 10:28:37 -07:00
pid.c xarray: add the xa_lock to the radix_tree_root 2018-04-11 10:28:39 -07:00
pid_namespace.c Merge branch 'userns-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2018-04-03 19:15:32 -07:00
profile.c
ptrace.c pids: introduce find_get_task_by_vpid() helper 2018-02-06 18:32:46 -08:00
range.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
reboot.c kernel/reboot.c: add devm_register_reboot_notifier() 2017-11-17 16:10:04 -08:00
relay.c kernel/relay.c: limit kmalloc size to KMALLOC_MAX_SIZE 2018-02-21 15:35:43 -08:00
resource.c resource: fix integer overflow at reallocation 2018-04-13 17:10:27 -07:00
seccomp.c - Fix seccomp GET_METADATA to deal with field sizes correctly (Tycho Andersen) 2018-02-22 10:50:24 -08:00
signal.c Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2018-04-07 11:11:41 -07:00
smp.c smp/core: Use lockdep to assert IRQs are disabled/enabled 2017-11-08 11:13:50 +01:00
smpboot.c watchdog/core, powerpc: Lock cpus across reconfiguration 2017-10-04 10:53:54 +02:00
smpboot.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
softirq.c softirq: Consolidate common code in tasklet_[hi]_action() 2018-03-09 11:50:55 +01:00
stacktrace.c
stop_machine.c
sys.c kernel: add ksys_setsid() helper; remove in-kernel call to sys_setsid() 2018-04-02 20:16:06 +02:00
sys_ni.c syscalls/core: Prepare CONFIG_ARCH_HAS_SYSCALL_WRAPPER=y for compat syscalls 2018-04-05 16:59:38 +02:00
sysctl.c kernel/sysctl.c: add kdoc comments to do_proc_do{u}intvec_minmax_conv_param 2018-04-11 10:28:38 -07:00
sysctl_binary.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
task_work.c locking/barriers: Convert users of lockless_dereference() to READ_ONCE() 2017-12-17 13:57:15 +01:00
taskstats.c pids: introduce find_get_task_by_vpid() helper 2018-02-06 18:32:46 -08:00
test_kprobes.c kprobes: Disable the jprobes test code 2017-10-20 11:02:54 +02:00
torture.c torture: Save a line in stutter_wait(): while -> for 2017-12-11 09:18:30 -08:00
tracepoint.c tracepoint: Remove smp_read_barrier_depends() from comment 2017-12-04 10:52:56 -08:00
tsacct.c
ucount.c headers: untangle kmemleak.h from mm.h 2018-04-05 21:36:27 -07:00
uid16.c fs: add do_fchownat(), ksys_fchown() helpers and ksys_{,l}chown() wrappers 2018-04-02 20:15:59 +02:00
uid16.h kernel: provide ksys_*() wrappers for syscalls called by kernel/uid16.c 2018-04-02 20:15:30 +02:00
umh.c kernel: use kernel_wait4() instead of sys_wait4() 2018-04-02 20:14:51 +02:00
up.c
user-return-notifier.c
user.c efivarfs: Limit the rate for non-root to read files 2018-02-22 10:21:02 -08:00
user_namespace.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2017-11-16 12:20:15 -08:00
utsname.c uts: create "struct uts_namespace" from kmem_cache 2018-04-11 10:28:35 -07:00
utsname_sysctl.c
watchdog.c Merge branch 'linus' into sched/core, to pick up fixes 2017-11-08 10:17:15 +01:00
watchdog_hld.c Merge branch 'linus' into core/urgent, to pick up dependent commits 2017-11-04 08:53:04 +01:00
workqueue.c Merge branch 'for-4.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2018-04-03 18:00:13 -07:00
workqueue_internal.h Merge branch 'for-4.14-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2017-11-06 12:26:49 -08:00