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![Mel Gorman](/assets/img/avatar_default.png)
Commit c0ff7453bb
("cpuset,mm: fix no node to alloc memory when
changing cpuset's mems") wins a super prize for the largest number of
memory barriers entered into fast paths for one commit.
[get|put]_mems_allowed is incredibly heavy with pairs of full memory
barriers inserted into a number of hot paths. This was detected while
investigating at large page allocator slowdown introduced some time
after 2.6.32. The largest portion of this overhead was shown by
oprofile to be at an mfence introduced by this commit into the page
allocator hot path.
For extra style points, the commit introduced the use of yield() in an
implementation of what looks like a spinning mutex.
This patch replaces the full memory barriers on both read and write
sides with a sequence counter with just read barriers on the fast path
side. This is much cheaper on some architectures, including x86. The
main bulk of the patch is the retry logic if the nodemask changes in a
manner that can cause a false failure.
While updating the nodemask, a check is made to see if a false failure
is a risk. If it is, the sequence number gets bumped and parallel
allocators will briefly stall while the nodemask update takes place.
In a page fault test microbenchmark, oprofile samples from
__alloc_pages_nodemask went from 4.53% of all samples to 1.15%. The
actual results were
3.3.0-rc3 3.3.0-rc3
rc3-vanilla nobarrier-v2r1
Clients 1 UserTime 0.07 ( 0.00%) 0.08 (-14.19%)
Clients 2 UserTime 0.07 ( 0.00%) 0.07 ( 2.72%)
Clients 4 UserTime 0.08 ( 0.00%) 0.07 ( 3.29%)
Clients 1 SysTime 0.70 ( 0.00%) 0.65 ( 6.65%)
Clients 2 SysTime 0.85 ( 0.00%) 0.82 ( 3.65%)
Clients 4 SysTime 1.41 ( 0.00%) 1.41 ( 0.32%)
Clients 1 WallTime 0.77 ( 0.00%) 0.74 ( 4.19%)
Clients 2 WallTime 0.47 ( 0.00%) 0.45 ( 3.73%)
Clients 4 WallTime 0.38 ( 0.00%) 0.37 ( 1.58%)
Clients 1 Flt/sec/cpu 497620.28 ( 0.00%) 520294.53 ( 4.56%)
Clients 2 Flt/sec/cpu 414639.05 ( 0.00%) 429882.01 ( 3.68%)
Clients 4 Flt/sec/cpu 257959.16 ( 0.00%) 258761.48 ( 0.31%)
Clients 1 Flt/sec 495161.39 ( 0.00%) 517292.87 ( 4.47%)
Clients 2 Flt/sec 820325.95 ( 0.00%) 850289.77 ( 3.65%)
Clients 4 Flt/sec 1020068.93 ( 0.00%) 1022674.06 ( 0.26%)
MMTests Statistics: duration
Sys Time Running Test (seconds) 135.68 132.17
User+Sys Time Running Test (seconds) 164.2 160.13
Total Elapsed Time (seconds) 123.46 120.87
The overall improvement is small but the System CPU time is much
improved and roughly in correlation to what oprofile reported (these
performance figures are without profiling so skew is expected). The
actual number of page faults is noticeably improved.
For benchmarks like kernel builds, the overall benefit is marginal but
the system CPU time is slightly reduced.
To test the actual bug the commit fixed I opened two terminals. The
first ran within a cpuset and continually ran a small program that
faulted 100M of anonymous data. In a second window, the nodemask of the
cpuset was continually randomised in a loop.
Without the commit, the program would fail every so often (usually
within 10 seconds) and obviously with the commit everything worked fine.
With this patch applied, it also worked fine so the fix should be
functionally equivalent.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
217 lines
5.7 KiB
C
217 lines
5.7 KiB
C
#ifndef _LINUX__INIT_TASK_H
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#define _LINUX__INIT_TASK_H
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#include <linux/rcupdate.h>
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#include <linux/irqflags.h>
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#include <linux/utsname.h>
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#include <linux/lockdep.h>
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#include <linux/ftrace.h>
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#include <linux/ipc.h>
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#include <linux/pid_namespace.h>
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#include <linux/user_namespace.h>
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#include <linux/securebits.h>
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#include <net/net_namespace.h>
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#ifdef CONFIG_SMP
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# define INIT_PUSHABLE_TASKS(tsk) \
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.pushable_tasks = PLIST_NODE_INIT(tsk.pushable_tasks, MAX_PRIO),
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#else
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# define INIT_PUSHABLE_TASKS(tsk)
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#endif
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extern struct files_struct init_files;
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extern struct fs_struct init_fs;
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#ifdef CONFIG_CGROUPS
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#define INIT_GROUP_RWSEM(sig) \
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.group_rwsem = __RWSEM_INITIALIZER(sig.group_rwsem),
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#else
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#define INIT_GROUP_RWSEM(sig)
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#endif
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#ifdef CONFIG_CPUSETS
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#define INIT_CPUSET_SEQ \
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.mems_allowed_seq = SEQCNT_ZERO,
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#else
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#define INIT_CPUSET_SEQ
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#endif
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#define INIT_SIGNALS(sig) { \
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.nr_threads = 1, \
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.wait_chldexit = __WAIT_QUEUE_HEAD_INITIALIZER(sig.wait_chldexit),\
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.shared_pending = { \
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.list = LIST_HEAD_INIT(sig.shared_pending.list), \
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.signal = {{0}}}, \
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.posix_timers = LIST_HEAD_INIT(sig.posix_timers), \
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.cpu_timers = INIT_CPU_TIMERS(sig.cpu_timers), \
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.rlim = INIT_RLIMITS, \
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.cputimer = { \
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.cputime = INIT_CPUTIME, \
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.running = 0, \
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.lock = __RAW_SPIN_LOCK_UNLOCKED(sig.cputimer.lock), \
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}, \
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.cred_guard_mutex = \
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__MUTEX_INITIALIZER(sig.cred_guard_mutex), \
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INIT_GROUP_RWSEM(sig) \
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}
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extern struct nsproxy init_nsproxy;
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#define INIT_SIGHAND(sighand) { \
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.count = ATOMIC_INIT(1), \
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.action = { { { .sa_handler = SIG_DFL, } }, }, \
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.siglock = __SPIN_LOCK_UNLOCKED(sighand.siglock), \
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.signalfd_wqh = __WAIT_QUEUE_HEAD_INITIALIZER(sighand.signalfd_wqh), \
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}
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extern struct group_info init_groups;
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#define INIT_STRUCT_PID { \
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.count = ATOMIC_INIT(1), \
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.tasks = { \
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{ .first = NULL }, \
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{ .first = NULL }, \
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{ .first = NULL }, \
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}, \
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.level = 0, \
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.numbers = { { \
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.nr = 0, \
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.ns = &init_pid_ns, \
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.pid_chain = { .next = NULL, .pprev = NULL }, \
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}, } \
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}
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#define INIT_PID_LINK(type) \
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{ \
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.node = { \
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.next = NULL, \
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.pprev = NULL, \
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}, \
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.pid = &init_struct_pid, \
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}
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#ifdef CONFIG_AUDITSYSCALL
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#define INIT_IDS \
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.loginuid = -1, \
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.sessionid = -1,
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#else
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#define INIT_IDS
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#endif
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#ifdef CONFIG_RCU_BOOST
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#define INIT_TASK_RCU_BOOST() \
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.rcu_boost_mutex = NULL,
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#else
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#define INIT_TASK_RCU_BOOST()
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#endif
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#ifdef CONFIG_TREE_PREEMPT_RCU
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#define INIT_TASK_RCU_TREE_PREEMPT() \
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.rcu_blocked_node = NULL,
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#else
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#define INIT_TASK_RCU_TREE_PREEMPT(tsk)
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#endif
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#ifdef CONFIG_PREEMPT_RCU
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#define INIT_TASK_RCU_PREEMPT(tsk) \
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.rcu_read_lock_nesting = 0, \
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.rcu_read_unlock_special = 0, \
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.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \
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INIT_TASK_RCU_TREE_PREEMPT() \
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INIT_TASK_RCU_BOOST()
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#else
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#define INIT_TASK_RCU_PREEMPT(tsk)
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#endif
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extern struct cred init_cred;
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#ifdef CONFIG_PERF_EVENTS
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# define INIT_PERF_EVENTS(tsk) \
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.perf_event_mutex = \
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__MUTEX_INITIALIZER(tsk.perf_event_mutex), \
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.perf_event_list = LIST_HEAD_INIT(tsk.perf_event_list),
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#else
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# define INIT_PERF_EVENTS(tsk)
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#endif
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#define INIT_TASK_COMM "swapper"
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/*
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* INIT_TASK is used to set up the first task table, touch at
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* your own risk!. Base=0, limit=0x1fffff (=2MB)
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*/
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#define INIT_TASK(tsk) \
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{ \
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.state = 0, \
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.stack = &init_thread_info, \
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.usage = ATOMIC_INIT(2), \
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.flags = PF_KTHREAD, \
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.prio = MAX_PRIO-20, \
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.static_prio = MAX_PRIO-20, \
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.normal_prio = MAX_PRIO-20, \
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.policy = SCHED_NORMAL, \
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.cpus_allowed = CPU_MASK_ALL, \
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.mm = NULL, \
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.active_mm = &init_mm, \
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.se = { \
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.group_node = LIST_HEAD_INIT(tsk.se.group_node), \
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}, \
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.rt = { \
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.run_list = LIST_HEAD_INIT(tsk.rt.run_list), \
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.time_slice = RR_TIMESLICE, \
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.nr_cpus_allowed = NR_CPUS, \
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}, \
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.tasks = LIST_HEAD_INIT(tsk.tasks), \
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INIT_PUSHABLE_TASKS(tsk) \
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.ptraced = LIST_HEAD_INIT(tsk.ptraced), \
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.ptrace_entry = LIST_HEAD_INIT(tsk.ptrace_entry), \
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.real_parent = &tsk, \
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.parent = &tsk, \
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.children = LIST_HEAD_INIT(tsk.children), \
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.sibling = LIST_HEAD_INIT(tsk.sibling), \
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.group_leader = &tsk, \
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RCU_INIT_POINTER(.real_cred, &init_cred), \
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RCU_INIT_POINTER(.cred, &init_cred), \
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.comm = INIT_TASK_COMM, \
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.thread = INIT_THREAD, \
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.fs = &init_fs, \
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.files = &init_files, \
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.signal = &init_signals, \
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.sighand = &init_sighand, \
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.nsproxy = &init_nsproxy, \
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.pending = { \
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.list = LIST_HEAD_INIT(tsk.pending.list), \
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.signal = {{0}}}, \
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.blocked = {{0}}, \
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.alloc_lock = __SPIN_LOCK_UNLOCKED(tsk.alloc_lock), \
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.journal_info = NULL, \
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.cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \
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.pi_lock = __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock), \
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.timer_slack_ns = 50000, /* 50 usec default slack */ \
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.pids = { \
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[PIDTYPE_PID] = INIT_PID_LINK(PIDTYPE_PID), \
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[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID), \
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[PIDTYPE_SID] = INIT_PID_LINK(PIDTYPE_SID), \
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}, \
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.thread_group = LIST_HEAD_INIT(tsk.thread_group), \
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INIT_IDS \
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INIT_PERF_EVENTS(tsk) \
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INIT_TRACE_IRQFLAGS \
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INIT_LOCKDEP \
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INIT_FTRACE_GRAPH \
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INIT_TRACE_RECURSION \
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INIT_TASK_RCU_PREEMPT(tsk) \
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INIT_CPUSET_SEQ \
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}
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#define INIT_CPU_TIMERS(cpu_timers) \
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{ \
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LIST_HEAD_INIT(cpu_timers[0]), \
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LIST_HEAD_INIT(cpu_timers[1]), \
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LIST_HEAD_INIT(cpu_timers[2]), \
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}
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/* Attach to the init_task data structure for proper alignment */
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#define __init_task_data __attribute__((__section__(".data..init_task")))
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#endif
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