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![Barret Rhoden](/assets/img/avatar_default.png)
Unnecessarily grabbing the tasklist_lock can be a scalability bottleneck for workloads that also must grab the tasklist_lock for waiting, killing, and cloning. The tasklist_lock was grabbed to protect tsk->sighand from disappearing (becoming NULL). tsk->signal was already protected by holding a reference to tsk. update_rlimit_cpu() assumed tsk->sighand != NULL. With this commit, it attempts to lock_task_sighand(). However, this means that update_rlimit_cpu() can fail. This only happens when a task is exiting. Note that during exec, sighand may *change*, but it will not be NULL. Prior to this commit, the do_prlimit() ensured that update_rlimit_cpu() would not fail by read locking the tasklist_lock and checking tsk->sighand != NULL. If update_rlimit_cpu() fails, there may be other tasks that are not exiting that share tsk->signal. However, the group_leader is the last task to be released, so if we cannot update_rlimit_cpu(group_leader), then the entire process is exiting. The only other caller of update_rlimit_cpu() is selinux_bprm_committing_creds(). It has tsk == current, so update_rlimit_cpu() cannot fail (current->sighand cannot disappear until current exits). This change resulted in a 14% speedup on a microbenchmark where parents kill and wait on their children, and children getpriority, setpriority, and getrlimit. Signed-off-by: Barret Rhoden <brho@google.com> Link: https://lkml.kernel.org/r/20220106172041.522167-4-brho@google.com Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
259 lines
7 KiB
C
259 lines
7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _linux_POSIX_TIMERS_H
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#define _linux_POSIX_TIMERS_H
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#include <linux/spinlock.h>
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#include <linux/list.h>
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#include <linux/alarmtimer.h>
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#include <linux/timerqueue.h>
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#include <linux/task_work.h>
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struct kernel_siginfo;
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struct task_struct;
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/*
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* Bit fields within a clockid:
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*
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* The most significant 29 bits hold either a pid or a file descriptor.
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*
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* Bit 2 indicates whether a cpu clock refers to a thread or a process.
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*
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* Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
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*
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* A clockid is invalid if bits 2, 1, and 0 are all set.
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*/
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#define CPUCLOCK_PID(clock) ((pid_t) ~((clock) >> 3))
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#define CPUCLOCK_PERTHREAD(clock) \
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(((clock) & (clockid_t) CPUCLOCK_PERTHREAD_MASK) != 0)
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#define CPUCLOCK_PERTHREAD_MASK 4
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#define CPUCLOCK_WHICH(clock) ((clock) & (clockid_t) CPUCLOCK_CLOCK_MASK)
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#define CPUCLOCK_CLOCK_MASK 3
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#define CPUCLOCK_PROF 0
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#define CPUCLOCK_VIRT 1
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#define CPUCLOCK_SCHED 2
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#define CPUCLOCK_MAX 3
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#define CLOCKFD CPUCLOCK_MAX
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#define CLOCKFD_MASK (CPUCLOCK_PERTHREAD_MASK|CPUCLOCK_CLOCK_MASK)
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static inline clockid_t make_process_cpuclock(const unsigned int pid,
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const clockid_t clock)
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{
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return ((~pid) << 3) | clock;
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}
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static inline clockid_t make_thread_cpuclock(const unsigned int tid,
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const clockid_t clock)
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{
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return make_process_cpuclock(tid, clock | CPUCLOCK_PERTHREAD_MASK);
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}
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static inline clockid_t fd_to_clockid(const int fd)
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{
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return make_process_cpuclock((unsigned int) fd, CLOCKFD);
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}
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static inline int clockid_to_fd(const clockid_t clk)
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{
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return ~(clk >> 3);
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}
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#ifdef CONFIG_POSIX_TIMERS
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/**
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* cpu_timer - Posix CPU timer representation for k_itimer
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* @node: timerqueue node to queue in the task/sig
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* @head: timerqueue head on which this timer is queued
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* @task: Pointer to target task
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* @elist: List head for the expiry list
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* @firing: Timer is currently firing
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*/
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struct cpu_timer {
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struct timerqueue_node node;
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struct timerqueue_head *head;
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struct pid *pid;
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struct list_head elist;
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int firing;
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};
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static inline bool cpu_timer_enqueue(struct timerqueue_head *head,
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struct cpu_timer *ctmr)
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{
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ctmr->head = head;
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return timerqueue_add(head, &ctmr->node);
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}
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static inline bool cpu_timer_queued(struct cpu_timer *ctmr)
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{
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return !!ctmr->head;
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}
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static inline bool cpu_timer_dequeue(struct cpu_timer *ctmr)
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{
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if (cpu_timer_queued(ctmr)) {
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timerqueue_del(ctmr->head, &ctmr->node);
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ctmr->head = NULL;
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return true;
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}
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return false;
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}
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static inline u64 cpu_timer_getexpires(struct cpu_timer *ctmr)
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{
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return ctmr->node.expires;
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}
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static inline void cpu_timer_setexpires(struct cpu_timer *ctmr, u64 exp)
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{
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ctmr->node.expires = exp;
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}
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/**
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* posix_cputimer_base - Container per posix CPU clock
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* @nextevt: Earliest-expiration cache
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* @tqhead: timerqueue head for cpu_timers
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*/
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struct posix_cputimer_base {
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u64 nextevt;
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struct timerqueue_head tqhead;
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};
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/**
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* posix_cputimers - Container for posix CPU timer related data
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* @bases: Base container for posix CPU clocks
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* @timers_active: Timers are queued.
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* @expiry_active: Timer expiry is active. Used for
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* process wide timers to avoid multiple
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* task trying to handle expiry concurrently
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*
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* Used in task_struct and signal_struct
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*/
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struct posix_cputimers {
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struct posix_cputimer_base bases[CPUCLOCK_MAX];
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unsigned int timers_active;
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unsigned int expiry_active;
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};
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/**
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* posix_cputimers_work - Container for task work based posix CPU timer expiry
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* @work: The task work to be scheduled
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* @scheduled: @work has been scheduled already, no further processing
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*/
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struct posix_cputimers_work {
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struct callback_head work;
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unsigned int scheduled;
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};
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static inline void posix_cputimers_init(struct posix_cputimers *pct)
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{
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memset(pct, 0, sizeof(*pct));
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pct->bases[0].nextevt = U64_MAX;
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pct->bases[1].nextevt = U64_MAX;
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pct->bases[2].nextevt = U64_MAX;
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}
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void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit);
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static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
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u64 runtime)
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{
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pct->bases[CPUCLOCK_SCHED].nextevt = runtime;
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}
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/* Init task static initializer */
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#define INIT_CPU_TIMERBASE(b) { \
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.nextevt = U64_MAX, \
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}
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#define INIT_CPU_TIMERBASES(b) { \
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INIT_CPU_TIMERBASE(b[0]), \
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INIT_CPU_TIMERBASE(b[1]), \
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INIT_CPU_TIMERBASE(b[2]), \
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}
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#define INIT_CPU_TIMERS(s) \
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.posix_cputimers = { \
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.bases = INIT_CPU_TIMERBASES(s.posix_cputimers.bases), \
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},
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#else
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struct posix_cputimers { };
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struct cpu_timer { };
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#define INIT_CPU_TIMERS(s)
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static inline void posix_cputimers_init(struct posix_cputimers *pct) { }
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static inline void posix_cputimers_group_init(struct posix_cputimers *pct,
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u64 cpu_limit) { }
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#endif
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#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
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void clear_posix_cputimers_work(struct task_struct *p);
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void posix_cputimers_init_work(void);
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#else
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static inline void clear_posix_cputimers_work(struct task_struct *p) { }
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static inline void posix_cputimers_init_work(void) { }
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#endif
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#define REQUEUE_PENDING 1
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/**
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* struct k_itimer - POSIX.1b interval timer structure.
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* @list: List head for binding the timer to signals->posix_timers
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* @t_hash: Entry in the posix timer hash table
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* @it_lock: Lock protecting the timer
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* @kclock: Pointer to the k_clock struct handling this timer
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* @it_clock: The posix timer clock id
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* @it_id: The posix timer id for identifying the timer
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* @it_active: Marker that timer is active
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* @it_overrun: The overrun counter for pending signals
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* @it_overrun_last: The overrun at the time of the last delivered signal
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* @it_requeue_pending: Indicator that timer waits for being requeued on
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* signal delivery
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* @it_sigev_notify: The notify word of sigevent struct for signal delivery
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* @it_interval: The interval for periodic timers
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* @it_signal: Pointer to the creators signal struct
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* @it_pid: The pid of the process/task targeted by the signal
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* @it_process: The task to wakeup on clock_nanosleep (CPU timers)
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* @sigq: Pointer to preallocated sigqueue
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* @it: Union representing the various posix timer type
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* internals.
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* @rcu: RCU head for freeing the timer.
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*/
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struct k_itimer {
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struct list_head list;
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struct hlist_node t_hash;
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spinlock_t it_lock;
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const struct k_clock *kclock;
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clockid_t it_clock;
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timer_t it_id;
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int it_active;
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s64 it_overrun;
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s64 it_overrun_last;
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int it_requeue_pending;
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int it_sigev_notify;
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ktime_t it_interval;
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struct signal_struct *it_signal;
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union {
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struct pid *it_pid;
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struct task_struct *it_process;
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};
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struct sigqueue *sigq;
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union {
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struct {
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struct hrtimer timer;
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} real;
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struct cpu_timer cpu;
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struct {
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struct alarm alarmtimer;
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} alarm;
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} it;
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struct rcu_head rcu;
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};
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void run_posix_cpu_timers(void);
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void posix_cpu_timers_exit(struct task_struct *task);
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void posix_cpu_timers_exit_group(struct task_struct *task);
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void set_process_cpu_timer(struct task_struct *task, unsigned int clock_idx,
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u64 *newval, u64 *oldval);
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int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new);
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void posixtimer_rearm(struct kernel_siginfo *info);
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#endif
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