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![Marco Elver](/assets/img/avatar_default.png)
This adds support for scoped accesses, where the memory range is checked for the duration of the scope. The feature is implemented by inserting the relevant access information into a list of scoped accesses for the current execution context, which are then checked (until removed) on every call (through instrumentation) into the KCSAN runtime. An alternative, more complex, implementation could set up a watchpoint for the scoped access, and keep the watchpoint set up. This, however, would require first exposing a handle to the watchpoint, as well as dealing with cases such as accesses by the same thread while the watchpoint is still set up (and several more cases). It is also doubtful if this would provide any benefit, since the majority of delay where the watchpoint is set up is likely due to the injected delays by KCSAN. Therefore, the implementation in this patch is simpler and avoids hurting KCSAN's main use-case (normal data race detection); it also implicitly increases scoped-access race-detection-ability due to increased probability of setting up watchpoints by repeatedly calling __kcsan_check_access() throughout the scope of the access. The implementation required adding an additional conditional branch to the fast-path. However, the microbenchmark showed a *speedup* of ~5% on the fast-path. This appears to be due to subtly improved codegen by GCC from moving get_ctx() and associated load of preempt_count earlier. Suggested-by: Boqun Feng <boqun.feng@gmail.com> Suggested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
203 lines
5.5 KiB
C
203 lines
5.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/init_task.h>
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#include <linux/export.h>
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#include <linux/mqueue.h>
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#include <linux/sched.h>
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#include <linux/sched/sysctl.h>
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#include <linux/sched/rt.h>
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#include <linux/sched/task.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/mm.h>
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#include <linux/audit.h>
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#include <linux/numa.h>
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#include <asm/pgtable.h>
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#include <linux/uaccess.h>
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static struct signal_struct init_signals = {
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.nr_threads = 1,
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.thread_head = LIST_HEAD_INIT(init_task.thread_node),
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.wait_chldexit = __WAIT_QUEUE_HEAD_INITIALIZER(init_signals.wait_chldexit),
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.shared_pending = {
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.list = LIST_HEAD_INIT(init_signals.shared_pending.list),
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.signal = {{0}}
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},
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.multiprocess = HLIST_HEAD_INIT,
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.rlim = INIT_RLIMITS,
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.cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex),
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#ifdef CONFIG_POSIX_TIMERS
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.posix_timers = LIST_HEAD_INIT(init_signals.posix_timers),
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.cputimer = {
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.cputime_atomic = INIT_CPUTIME_ATOMIC,
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},
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#endif
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INIT_CPU_TIMERS(init_signals)
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.pids = {
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[PIDTYPE_PID] = &init_struct_pid,
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[PIDTYPE_TGID] = &init_struct_pid,
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[PIDTYPE_PGID] = &init_struct_pid,
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[PIDTYPE_SID] = &init_struct_pid,
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},
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INIT_PREV_CPUTIME(init_signals)
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};
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static struct sighand_struct init_sighand = {
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.count = REFCOUNT_INIT(1),
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.action = { { { .sa_handler = SIG_DFL, } }, },
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.siglock = __SPIN_LOCK_UNLOCKED(init_sighand.siglock),
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.signalfd_wqh = __WAIT_QUEUE_HEAD_INITIALIZER(init_sighand.signalfd_wqh),
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};
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/*
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* Set up the first task table, touch at your own risk!. Base=0,
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* limit=0x1fffff (=2MB)
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*/
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struct task_struct init_task
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#ifdef CONFIG_ARCH_TASK_STRUCT_ON_STACK
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__init_task_data
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#endif
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= {
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#ifdef CONFIG_THREAD_INFO_IN_TASK
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.thread_info = INIT_THREAD_INFO(init_task),
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.stack_refcount = REFCOUNT_INIT(1),
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#endif
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.state = 0,
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.stack = init_stack,
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.usage = REFCOUNT_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_ptr = &init_task.cpus_mask,
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.cpus_mask = CPU_MASK_ALL,
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.nr_cpus_allowed= NR_CPUS,
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.mm = NULL,
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.active_mm = &init_mm,
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.restart_block = {
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.fn = do_no_restart_syscall,
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},
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.se = {
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.group_node = LIST_HEAD_INIT(init_task.se.group_node),
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},
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.rt = {
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.run_list = LIST_HEAD_INIT(init_task.rt.run_list),
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.time_slice = RR_TIMESLICE,
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},
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.tasks = LIST_HEAD_INIT(init_task.tasks),
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#ifdef CONFIG_SMP
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.pushable_tasks = PLIST_NODE_INIT(init_task.pushable_tasks, MAX_PRIO),
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#endif
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#ifdef CONFIG_CGROUP_SCHED
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.sched_task_group = &root_task_group,
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#endif
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.ptraced = LIST_HEAD_INIT(init_task.ptraced),
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.ptrace_entry = LIST_HEAD_INIT(init_task.ptrace_entry),
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.real_parent = &init_task,
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.parent = &init_task,
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.children = LIST_HEAD_INIT(init_task.children),
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.sibling = LIST_HEAD_INIT(init_task.sibling),
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.group_leader = &init_task,
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RCU_POINTER_INITIALIZER(real_cred, &init_cred),
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RCU_POINTER_INITIALIZER(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(init_task.pending.list),
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.signal = {{0}}
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},
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.blocked = {{0}},
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.alloc_lock = __SPIN_LOCK_UNLOCKED(init_task.alloc_lock),
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.journal_info = NULL,
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INIT_CPU_TIMERS(init_task)
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.pi_lock = __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
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.timer_slack_ns = 50000, /* 50 usec default slack */
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.thread_pid = &init_struct_pid,
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.thread_group = LIST_HEAD_INIT(init_task.thread_group),
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.thread_node = LIST_HEAD_INIT(init_signals.thread_head),
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#ifdef CONFIG_AUDIT
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.loginuid = INVALID_UID,
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.sessionid = AUDIT_SID_UNSET,
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#endif
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#ifdef CONFIG_PERF_EVENTS
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.perf_event_mutex = __MUTEX_INITIALIZER(init_task.perf_event_mutex),
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.perf_event_list = LIST_HEAD_INIT(init_task.perf_event_list),
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#endif
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#ifdef CONFIG_PREEMPT_RCU
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.rcu_read_lock_nesting = 0,
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.rcu_read_unlock_special.s = 0,
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.rcu_node_entry = LIST_HEAD_INIT(init_task.rcu_node_entry),
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.rcu_blocked_node = NULL,
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#endif
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#ifdef CONFIG_TASKS_RCU
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.rcu_tasks_holdout = false,
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.rcu_tasks_holdout_list = LIST_HEAD_INIT(init_task.rcu_tasks_holdout_list),
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.rcu_tasks_idle_cpu = -1,
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#endif
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#ifdef CONFIG_CPUSETS
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.mems_allowed_seq = SEQCNT_ZERO(init_task.mems_allowed_seq),
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#endif
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#ifdef CONFIG_RT_MUTEXES
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.pi_waiters = RB_ROOT_CACHED,
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.pi_top_task = NULL,
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#endif
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INIT_PREV_CPUTIME(init_task)
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#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
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.vtime.seqcount = SEQCNT_ZERO(init_task.vtime_seqcount),
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.vtime.starttime = 0,
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.vtime.state = VTIME_SYS,
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#endif
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#ifdef CONFIG_NUMA_BALANCING
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.numa_preferred_nid = NUMA_NO_NODE,
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.numa_group = NULL,
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.numa_faults = NULL,
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#endif
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#ifdef CONFIG_KASAN
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.kasan_depth = 1,
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#endif
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#ifdef CONFIG_KCSAN
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.kcsan_ctx = {
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.disable_count = 0,
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.atomic_next = 0,
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.atomic_nest_count = 0,
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.in_flat_atomic = false,
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.access_mask = 0,
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.scoped_accesses = {LIST_POISON1, NULL},
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},
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#endif
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#ifdef CONFIG_TRACE_IRQFLAGS
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.softirqs_enabled = 1,
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#endif
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#ifdef CONFIG_LOCKDEP
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.lockdep_depth = 0, /* no locks held yet */
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.curr_chain_key = INITIAL_CHAIN_KEY,
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.lockdep_recursion = 0,
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#endif
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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.ret_stack = NULL,
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#endif
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#if defined(CONFIG_TRACING) && defined(CONFIG_PREEMPTION)
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.trace_recursion = 0,
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#endif
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#ifdef CONFIG_LIVEPATCH
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.patch_state = KLP_UNDEFINED,
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#endif
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#ifdef CONFIG_SECURITY
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.security = NULL,
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#endif
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};
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EXPORT_SYMBOL(init_task);
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/*
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* Initial thread structure. Alignment of this is handled by a special
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* linker map entry.
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*/
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#ifndef CONFIG_THREAD_INFO_IN_TASK
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struct thread_info init_thread_info __init_thread_info = INIT_THREAD_INFO(init_task);
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#endif
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