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Chang S. Bae 6c3118c321 signal: Skip the altstack update when not needed 
== Background ==

Support for large, "dynamic" fpstates was recently merged.  This
included code to ensure that sigaltstacks are sufficiently sized for
these large states.  A new lock was added to remove races between
enabling large features and setting up sigaltstacks.

== Problem ==

The new lock (sigaltstack_lock()) is acquired in the sigreturn path
before restoring the old sigaltstack.  Unfortunately, contention on the
new lock causes a measurable signal handling performance regression [1].
However, the common case is that no *changes* are made to the
sigaltstack state at sigreturn.

== Solution ==

do_sigaltstack() acquires sigaltstack_lock() and is used for both
sys_sigaltstack() and restoring the sigaltstack in sys_sigreturn().
Check for changes to the sigaltstack before taking the lock.  If no
changes were made, return before acquiring the lock.

This removes lock contention from the common-case sigreturn path.

[1] https://lore.kernel.org/lkml/20211207012128.GA16074@xsang-OptiPlex-9020/

Fixes: 3aac3ebea0 ("x86/signal: Implement sigaltstack size validation")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20211210225503.12734-1-chang.seok.bae@intel.com
2021-12-14 13:08:36 -08:00
..
bpf bpf: Fix toctou on read-only map's constant scalar tracking 2021-11-15 20:47:07 -08:00
cgroup Merge branch 'akpm' (patches from Andrew) 2021-11-06 14:08:17 -07:00
configs drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
debug kdb: Adopt scheduler's task classification 2021-11-03 17:21:37 +00:00
dma dma-mapping updates for Linux 5.16 2021-11-09 10:56:41 -08:00
entry signal: Replace force_fatal_sig with force_exit_sig when in doubt 2021-11-19 09:15:58 -06:00
events perf: Ignore sigtrap for tracepoints destined for other tasks 2021-11-23 09:45:37 +01:00
futex futex: Fix PREEMPT_RT build 2021-10-19 17:27:05 +02:00
gcov Kconfig: Introduce ARCH_WANTS_NO_INSTR and CC_HAS_NO_PROFILE_FN_ATTR 2021-06-22 11:07:18 -07:00
irq PCI/MSI: Move non-mask check back into low level accessors 2021-11-11 09:50:30 +01:00
kcsan kcsan: selftest: Cleanup and add missing __init 2021-09-13 16:41:20 -07:00
livepatch Tracing updates for 5.16: 2021-11-01 20:05:19 -07:00
locking locking/rwsem: Optimize down_read_trylock() under highly contended case 2021-11-23 09:45:36 +01:00
power PM: hibernate: Fix snapshot partial write lengths 2021-11-24 13:50:18 +01:00
printk printk fixup for 5.16 2021-11-18 10:50:45 -08:00
rcu RCU pull request for v5.16 2021-11-01 20:25:38 -07:00
sched sched/uclamp: Fix rq->uclamp_max not set on first enqueue 2021-12-04 10:56:18 +01:00
time timers/nohz: Last resort update jiffies on nohz_full IRQ entry 2021-12-02 15:07:22 +01:00
trace tracing: Fix a kmemleak false positive in tracing_map 2021-12-01 21:04:34 -05:00
.gitignore .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
acct.c kernel: remove spurious blkdev.h includes 2021-10-18 06:17:01 -06:00
async.c kernel/async.c: remove async_unregister_domain() 2021-05-07 00:26:33 -07:00
audit.c lsm: separate security_task_getsecid() into subjective and objective variants 2021-03-22 15:23:32 -04:00
audit.h audit/stable-5.16 PR 20211101 2021-11-01 21:17:39 -07:00
audit_fsnotify.c fsnotify: clarify contract for create event hooks 2021-10-27 12:32:34 +02:00
audit_tree.c audit/stable-5.16 PR 20211101 2021-11-01 21:17:39 -07:00
audit_watch.c \n 2021-11-06 16:43:20 -07:00
auditfilter.c audit: add filtering for io_uring records 2021-09-19 22:34:38 -04:00
auditsc.c audit/stable-5.16 PR 20211101 2021-11-01 21:17:39 -07:00
backtracetest.c
bounds.c
capability.c
cfi.c cfi: Use rcu_read_{un}lock_sched_notrace 2021-08-11 13:11:12 -07:00
compat.c arch: remove compat_alloc_user_space 2021-09-08 15:32:35 -07:00
configs.c
context_tracking.c
cpu.c sched/scs: Reset task stack state in bringup_cpu() 2021-11-24 12:20:27 +01:00
cpu_pm.c PM: cpu: Make notifier chain use a raw_spinlock_t 2021-08-16 18:55:32 +02:00
crash_core.c kdump: use vmlinux_build_id to simplify 2021-07-08 11:48:22 -07:00
crash_dump.c
cred.c ucounts: In set_cred_ucounts assume new->ucounts is non-NULL 2021-10-20 10:45:34 -05:00
delayacct.c delayacct: Add sysctl to enable at runtime 2021-05-12 11:43:25 +02:00
dma.c
exec_domain.c
exit.c Merge branch 'per_signal_struct_coredumps-for-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-11-03 12:15:29 -07:00
extable.c extable: use is_kernel_text() helper 2021-11-09 10:02:51 -08:00
fail_function.c
fork.c A single fix for POSIX CPU timers to address a problem where POSIX CPU 2021-11-14 10:43:38 -08:00
freezer.c sched: Add get_current_state() 2021-06-18 11:43:08 +02:00
gen_kheaders.sh kbuild: clean up ${quiet} checks in shell scripts 2021-05-27 04:01:50 +09:00
groups.c groups: simplify struct group_info allocation 2021-02-26 09:41:03 -08:00
hung_task.c Merge branch 'akpm' (patches from Andrew) 2021-07-02 12:08:10 -07:00
iomem.c
irq_work.c irq_work: Also rcuwait for !IRQ_WORK_HARD_IRQ on PREEMPT_RT 2021-10-15 11:25:18 +02:00
jump_label.c jump_label: Fix jump_label_text_reserved() vs __init 2021-07-05 10:46:20 +02:00
kallsyms.c kallsyms: strip LTO suffixes from static functions 2021-10-04 10:58:25 -07:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks locking/rwlock: Provide RT variant 2021-08-17 17:50:51 +02:00
Kconfig.preempt preempt: Restore preemption model selection configs 2021-11-11 13:09:33 +01:00
kcov.c kcov: replace local_irq_save() with a local_lock_t 2021-11-09 10:02:52 -08:00
kexec.c kexec: avoid compat_alloc_user_space 2021-09-08 15:32:34 -07:00
kexec_core.c Merge branch 'rework/printk_safe-removal' into for-linus 2021-08-30 16:36:10 +02:00
kexec_elf.c
kexec_file.c memblock: add MEMBLOCK_DRIVER_MANAGED to mimic IORESOURCE_SYSRAM_DRIVER_MANAGED 2021-11-06 13:30:42 -07:00
kexec_internal.h kexec: move machine_kexec_post_load() to public interface 2021-02-22 12:33:26 +00:00
kheaders.c
kmod.c modules: add CONFIG_MODPROBE_PATH 2021-05-07 00:26:33 -07:00
kprobes.c kprobes: Limit max data_size of the kretprobe instances 2021-12-01 21:04:34 -05:00
ksysfs.c
kthread.c Merge branch 'exit-cleanups-for-v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-11-10 16:15:54 -08:00
latencytop.c
Makefile Tracing updates for 5.16: 2021-11-01 20:05:19 -07:00
module-internal.h
module.c module: change to print useful messages from elf_validity_check() 2021-11-05 15:13:10 -07:00
module_signature.c
module_signing.c
notifier.c notifier: Remove atomic_notifier_call_chain_robust() 2021-08-16 18:55:32 +02:00
nsproxy.c memcg: enable accounting for new namesapces and struct nsproxy 2021-09-03 09:58:12 -07:00
padata.c padata: Remove repeated verbose license text 2021-08-27 16:30:18 +08:00
panic.c Merge branch 'rework/printk_safe-removal' into for-linus 2021-08-30 16:36:10 +02:00
params.c params: lift param_set_uint_minmax to common code 2021-08-16 14:42:22 +02:00
pid.c pid: add pidfd_get_task() helper 2021-10-14 13:29:18 +02:00
pid_namespace.c memcg: enable accounting for new namesapces and struct nsproxy 2021-09-03 09:58:12 -07:00
profile.c profiling: fix shift-out-of-bounds bugs 2021-09-08 11:50:26 -07:00
ptrace.c sched: Change task_struct::state 2021-06-18 11:43:09 +02:00
range.c
reboot.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2021-11-12 11:53:16 -08:00
regset.c
relay.c
resource.c kernel/resource: disallow access to exclusive system RAM regions 2021-11-09 10:02:52 -08:00
resource_kunit.c
rseq.c KVM: rseq: Update rseq when processing NOTIFY_RESUME on xfer to KVM guest 2021-09-22 10:24:01 -04:00
scftorture.c scftorture: Warn on individual scf_torture_init() error conditions 2021-09-16 10:27:48 -07:00
scs.c scs: Release kasan vmalloc poison in scs_free process 2021-09-30 09:37:27 +01:00
seccomp.c Merge branch 'exit-cleanups-for-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-09-01 14:52:05 -07:00
signal.c signal: Skip the altstack update when not needed 2021-12-14 13:08:36 -08:00
smp.c sched: Improve wake_up_all_idle_cpus() take #2 2021-10-22 15:32:46 +02:00
smpboot.c smpboot: Replace deprecated CPU-hotplug functions. 2021-08-10 14:57:42 +02:00
smpboot.h
softirq.c timers/nohz: Last resort update jiffies on nohz_full IRQ entry 2021-12-02 15:07:22 +01:00
stackleak.c
stacktrace.c stacktrace: move filter_irq_stacks() to kernel/stacktrace.c 2021-11-06 13:30:43 -07:00
static_call.c static_call: Fix static_call_text_reserved() vs __init 2021-07-05 10:46:33 +02:00
stop_machine.c stop_machine: Add caller debug info to queue_stop_cpus_work 2021-03-23 16:01:58 +01:00
sys.c Merge branch 'akpm' (patches from Andrew) 2021-09-08 12:55:35 -07:00
sys_ni.c futex: Implement sys_futex_waitv() 2021-10-07 13:51:11 +02:00
sysctl-test.c kernel/sysctl-test: Remove some casts which are no-longer required 2021-06-23 16:41:24 -06:00
sysctl.c Merge branch 'akpm' (patches from Andrew) 2021-09-03 10:08:28 -07:00
task_work.c kasan: record task_work_add() call stack 2021-04-30 11:20:42 -07:00
taskstats.c
torture.c torture: Replace deprecated CPU-hotplug functions. 2021-08-10 10:48:07 -07:00
tracepoint.c tracepoint: Fix kerneldoc comments 2021-08-16 11:39:51 -04:00
tsacct.c mm/mmap.c: fix a data race of mm->total_vm 2021-11-06 13:30:35 -07:00
ucount.c ucounts: Use atomic_long_sub_return for clarity 2021-10-20 10:45:34 -05:00
uid16.c
uid16.h
umh.c kernel/umh.c: fix some spelling mistakes 2021-05-07 00:26:34 -07:00
up.c A set of locking related fixes and updates: 2021-05-09 13:07:03 -07:00
user-return-notifier.c
user.c fs/epoll: use a per-cpu counter for user's watches count 2021-09-08 11:50:27 -07:00
user_namespace.c memcg: enable accounting for new namesapces and struct nsproxy 2021-09-03 09:58:12 -07:00
usermode_driver.c Merge branch 'work.namei' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2021-07-03 11:41:14 -07:00
utsname.c
utsname_sysctl.c
watch_queue.c
watchdog.c kernel: watchdog: modify the explanation related to watchdog thread 2021-06-29 10:53:46 -07:00
watchdog_hld.c
workqueue.c Merge branch 'akpm' (patches from Andrew) 2021-11-06 14:08:17 -07:00
workqueue_internal.h workqueue: Assign a color to barrier work items 2021-08-17 07:49:10 -10:00