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5d65bc0ca1
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Li Zefan 5d65bc0ca1 cgroup: remove synchronize_rcu() from cgroup_attach_{task|proc}() 
These 2 syncronize_rcu()s make attaching a task to a cgroup
quite slow, and it can't be ignored in some situations.

A real case from Colin Cross: Android uses cgroups heavily to
manage thread priorities, putting threads in a background group
with reduced cpu.shares when they are not visible to the user,
and in a foreground group when they are. Some RPCs from foreground
threads to background threads will temporarily move the background
thread into the foreground group for the duration of the RPC.
This results in many calls to cgroup_attach_task.

In cgroup_attach_task() it's task->cgroups that is protected by RCU,
and put_css_set() calls kfree_rcu() to free it.

If we remove this synchronize_rcu(), there can be threads in RCU-read
sections accessing their old cgroup via current->cgroups with
concurrent rmdir operation, but this is safe.

 # time for ((i=0; i<50; i++)) { echo $$ > /mnt/sub/tasks; echo $$ > /mnt/tasks; }

real    0m2.524s
user    0m0.008s
sys     0m0.004s

With this patch:

real    0m0.004s
user    0m0.004s
sys     0m0.000s

tj: These synchronize_rcu()s are utterly confused.  synchornize_rcu()
    necessarily has to come between two operations to guarantee that
    the changes made by the former operation are visible to all rcu
    readers before proceeding to the latter operation.  Here,
    synchornize_rcu() are at the end of attach operations with nothing
    beyond it.  Its only effect would be delaying completion of
    write(2) to sysfs tasks/procs files until all rcu readers see the
    change, which doesn't mean anything.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Colin Cross <ccross@google.com>
2013-01-14 10:44:42 -08:00
..
debug KGDB/KDB fixes and cleanups 2012-10-13 11:16:58 +09:00
events Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2012-12-17 15:44:47 -08:00
gcov
irq irq: tsk->comm is an array 2012-12-18 15:02:11 -08:00
power Merge branch 'for-3.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2012-12-12 08:18:24 -08:00
sched sched: numa: ksm: fix oops in task_numa_placment() 2012-12-20 07:06:56 -08:00
time Merge tag 'kvm-3.8-1' of git://git.kernel.org/pub/scm/virt/kvm/kvm 2012-12-13 15:31:08 -08:00
trace Merge branch 'tip/perf/core-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace 2012-12-18 12:28:39 -08:00
.gitignore
acct.c vfs: make path_openat take a struct filename pointer 2012-10-12 20:15:09 -04:00
async.c [SCSI] async: make async_synchronize_full() flush all work regardless of domain 2012-07-20 09:07:37 +01:00
audit_tree.c fsnotify: pass group to fsnotify_destroy_mark() 2012-12-11 13:44:36 -05:00
audit_watch.c Merge branch 'for-next' of git://git.infradead.org/users/eparis/notify 2012-12-20 20:11:52 -08:00
audit.c fs: handle failed audit_log_start properly 2012-10-09 23:33:37 -04:00
audit.h audit: optimize audit_compare_dname_path 2012-10-12 00:32:02 -04:00
auditfilter.c audit: optimize audit_compare_dname_path 2012-10-12 00:32:02 -04:00
auditsc.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-12-12 12:22:13 -08:00
backtracetest.c
bounds.c
capability.c userns: Teach inode_capable to understand inodes whose uids map to other namespaces. 2012-05-15 14:59:24 -07:00
cgroup_freezer.c cgroup: rename ->create/post_create/pre_destroy/destroy() to ->css_alloc/online/offline/free() 2012-11-19 08:13:38 -08:00
cgroup.c cgroup: remove synchronize_rcu() from cgroup_attach_{task|proc}() 2013-01-14 10:44:42 -08:00
compat.c compat: generic compat_sys_sched_rr_get_interval() implementation 2012-12-17 17:15:18 -08:00
configs.c
context_tracking.c context_tracking: New context tracking susbsystem 2012-11-30 11:40:07 -08:00
cpu_pm.c kernel/cpu_pm.c: fix various typos 2012-05-31 17:49:27 -07:00
cpu.c Merge branch 'x86-bsp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-12-11 19:56:33 -08:00
cpuset.c cpuset: use N_MEMORY instead N_HIGH_MEMORY 2012-12-12 17:38:32 -08:00
crash_dump.c
cred.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2012-12-18 10:55:28 -08:00
delayacct.c
dma.c Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
elfcore.c
exec_domain.c
exit.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2012-12-17 15:44:47 -08:00
extable.c extable: Skip sorting if sorted at build time. 2012-04-19 15:06:55 -07:00
fork.c pidns: Outlaw thread creation after unshare(CLONE_NEWPID) 2012-12-24 22:53:14 -08:00
freezer.c freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() 2012-10-26 14:27:49 -07:00
futex_compat.c futex: Mark get_robust_list as deprecated 2012-03-29 11:37:17 +02:00
futex.c futex: avoid wake_futex() for a PI futex_q 2012-11-26 17:41:24 -08:00
groups.c userns: Convert in_group_p and in_egroup_p to use kgid_t 2012-05-03 03:29:33 -07:00
hrtimer.c hrtimer: Update hrtimer base offsets each hrtimer_interrupt 2012-07-11 23:34:39 +02:00
hung_task.c hung task debugging: Inject NMI when hung and going to panic 2012-04-25 12:39:25 +02:00
irq_work.c irq_work: fix compile failure on tile from missing include 2012-04-13 13:15:16 -04:00
itimer.c itimer: Use printk_once instead of WARN_ONCE 2012-04-10 11:00:30 +02:00
jump_label.c jump_label: Export jump_label_rate_limit() 2012-08-06 19:00:35 +03:00
kallsyms.c vsprintf: fix %ps on non symbols when using kallsyms 2012-05-29 16:22:32 -07:00
kcmp.c kcmp: include linux/ptrace.h 2012-12-20 17:40:19 -08:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks locking: Adjust spin lock inlining Kconfig options 2012-09-13 17:56:13 +02:00
Kconfig.preempt locking/kconfig: Simplify INLINE_SPIN_UNLOCK usage 2012-03-23 13:18:57 +01:00
kexec.c kdump: remove unneeded include 2012-10-06 03:05:19 +09:00
kfifo.c [media] kernel:kfifo: export __kfifo_max_r symbol 2012-04-11 18:24:37 -03:00
kmod.c Bury the conditionals from kernel_thread/kernel_execve series 2012-12-19 18:07:38 -05:00
kprobes.c kprobes/x86: Fix to support jprobes on ftrace-based kprobe 2012-09-13 22:52:11 -04:00
ksysfs.c Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-12-11 18:10:49 -08:00
kthread.c kthread: use N_MEMORY instead N_HIGH_MEMORY 2012-12-12 17:38:33 -08:00
latencytop.c
lglock.c brlocks/lglocks: turn into functions 2012-05-29 23:28:41 -04:00
lockdep_internals.h
lockdep_proc.c lockdep: Use KSYM_NAME_LEN'ed buffer for __get_key_name() 2012-10-24 12:39:09 +02:00
lockdep_states.h
lockdep.c lockdep: Check if nested lock is actually held 2012-09-13 17:00:44 +02:00
Makefile Nothing all that exciting; a new module-from-fd syscall for those who want 2012-12-19 07:55:08 -08:00
modsign_certificate.S MODSIGN: Avoid using .incbin in C source 2012-12-14 13:06:44 +10:30
modsign_pubkey.c keys: use keyring_alloc() to create module signing keyring 2012-12-20 17:40:21 -08:00
module_signing.c MODSIGN: Don't use enum-type bitfields in module signature info block 2012-12-05 11:27:24 +10:30
module-internal.h MODSIGN: Move the magic string to the end of a module and eliminate the search 2012-10-19 17:30:40 -07:00
module.c Nothing all that exciting; a new module-from-fd syscall for those who want 2012-12-19 07:55:08 -08:00
mutex-debug.c
mutex-debug.h
mutex.c
mutex.h
notifier.c
nsproxy.c userns: Implement unshare of the user namespace 2012-11-20 04:18:14 -08:00
padata.c padata: use __this_cpu_read per-cpu helper 2012-12-06 17:16:23 +08:00
panic.c panic: fix a possible deadlock in panic() 2012-07-30 17:25:13 -07:00
params.c params: replace printk(KERN_<LVL>...) with pr_<lvl>(...) 2012-05-04 17:28:18 -07:00
pid_namespace.c pidns: Stop pid allocation when init dies 2012-12-25 16:10:05 -08:00
pid.c pidns: Stop pid allocation when init dies 2012-12-25 16:10:05 -08:00
posix-cpu-timers.c A few /dev/random improvements for the v3.8 merge window. 2012-12-19 20:23:37 -08:00
posix-timers.c
printk.c printk: boot_delay should only affect output 2012-12-17 17:15:13 -08:00
profile.c propagate name change to comments in kernel source 2012-12-06 10:39:54 +01:00
ptrace.c Merge branch 'akpm' (Andrew's patch-bomb) 2012-12-17 20:58:12 -08:00
range.c
rcu.h rcu: Add a module parameter to force use of expedited RCU primitives 2012-10-23 14:54:08 -07:00
rcupdate.c rcu: Add a module parameter to force use of expedited RCU primitives 2012-10-23 14:54:08 -07:00
rcutiny_plugin.h rcu: Add a module parameter to force use of expedited RCU primitives 2012-10-23 14:54:08 -07:00
rcutiny.c rcu: Fix TINY_RCU rcu_is_cpu_rrupt_from_idle check 2012-11-13 14:08:34 -08:00
rcutorture.c Merge branches 'urgent.2012.10.27a', 'doc.2012.11.16a', 'fixes.2012.11.13a', 'srcu.2012.10.27a', 'stall.2012.11.13a', 'tracing.2012.11.08a' and 'idle.2012.10.24a' into HEAD 2012-11-16 09:59:58 -08:00
rcutree_plugin.h rcu: Separate accounting of callbacks from callback-free CPUs 2012-11-16 10:05:57 -08:00
rcutree_trace.c rcu: Separate accounting of callbacks from callback-free CPUs 2012-11-16 10:05:57 -08:00
rcutree.c context_tracking: New context tracking susbsystem 2012-11-30 11:40:07 -08:00
rcutree.h rcu: Separate accounting of callbacks from callback-free CPUs 2012-11-16 10:05:57 -08:00
relay.c splice: fix racy pipe->buffers uses 2012-06-13 21:16:42 +02:00
res_counter.c res_counter: return amount of charges after res_counter_uncharge() 2012-12-18 15:02:12 -08:00
resource.c kernel/resource.c: fix stack overflow in __reserve_region_with_split() 2012-10-06 03:05:31 +09:00
rtmutex_common.h
rtmutex-debug.c
rtmutex-debug.h
rtmutex-tester.c
rtmutex.c
rtmutex.h
rwsem.c Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
seccomp.c seccomp: Make syscall skipping and nr changes more consistent 2012-10-02 21:14:29 +10:00
semaphore.c semaphore: fix improper comment reference to mutex 2012-04-05 17:15:55 -07:00
signal.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2012-12-20 18:05:28 -08:00
smp.c smp: Remove ipi_call_lock[_irq]()/ipi_call_unlock[_irq]() 2012-06-05 17:27:14 +02:00
smpboot.c hotplug: Fix UP bug in smpboot hotplug code 2012-08-13 17:01:07 +02:00
smpboot.h smpboot: Provide infrastructure for percpu hotplug threads 2012-08-13 17:01:07 +02:00
softirq.c cputime: Specialize irq vtime hooks 2012-10-29 21:31:32 +01:00
spinlock.c locking/kconfig: Simplify INLINE_SPIN_UNLOCK usage 2012-03-23 13:18:57 +01:00
srcu.c Merge branches 'urgent.2012.10.27a', 'doc.2012.11.16a', 'fixes.2012.11.13a', 'srcu.2012.10.27a', 'stall.2012.11.13a', 'tracing.2012.11.08a' and 'idle.2012.10.24a' into HEAD 2012-11-16 09:59:58 -08:00
stacktrace.c
stop_machine.c
sys_ni.c module: add syscall to load module from fd 2012-12-14 13:05:22 +10:30
sys.c cputime: Rename thread_group_times to thread_group_cputime_adjusted 2012-11-28 17:07:57 +01:00
sysctl_binary.c pidns: Use task_active_pid_ns where appropriate 2012-11-19 05:59:09 -08:00
sysctl.c Automatic NUMA Balancing V11 2012-12-16 15:18:08 -08:00
task_work.c task_work: task_work_add() should not succeed after exit_task_work() 2012-09-13 16:47:34 +02:00
taskstats.c taskstats: cgroupstats_user_cmd() may leak on error 2012-10-06 03:05:31 +09:00
test_kprobes.c
time.c time: Move update_vsyscall definitions to timekeeper_internal.h 2012-09-24 12:38:06 -04:00
timeconst.pl
timer.c timers: Fix endless looping between cascade() and internal_add_timer() 2012-10-09 21:27:14 +02:00
tracepoint.c
tsacct.c userns: Convert taskstats to handle the user and pid namespaces. 2012-09-18 01:01:32 -07:00
uid16.c userns: Convert setting and getting uid and gid system calls to use kuid and kgid 2012-05-03 03:28:41 -07:00
up.c
user_namespace.c userns: Fix typo in description of the limitation of userns_install 2012-12-14 18:36:36 -08:00
user-return-notifier.c
user.c proc: Usable inode numbers for the namespace file descriptors. 2012-11-20 04:19:49 -08:00
utsname_sysctl.c
utsname.c userns: Require CAP_SYS_ADMIN for most uses of setns. 2012-12-14 16:12:03 -08:00
wait.c propagate name change to comments in kernel source 2012-12-06 10:39:54 +01:00
watchdog.c watchdog: Fix disable/enable regression 2012-12-19 12:10:33 -08:00
workqueue_sched.h
workqueue.c Merge branch 'for-3.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2012-12-12 08:15:13 -08:00