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posix-cpu-timers: Move state tracking to struct posix_cputimers 

Put it where it belongs and clean up the ifdeffery in fork completely.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190821192922.743229404@linutronix.de
This commit is contained in:
Thomas Gleixner 2019-08-21 21:09:24 +02:00
parent 8991afe264
commit 244d49e306
6 changed files with 54 additions and 50 deletions
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8
include/linux/posix-timers.h
View File

@ -77,15 +77,23 @@ struct posix_cputimer_base {
/**
* posix_cputimers - Container for posix CPU timer related data
* @bases: Base container for posix CPU clocks
* @timers_active: Timers are queued.
* @expiry_active: Timer expiry is active. Used for
* process wide timers to avoid multiple
* task trying to handle expiry concurrently
*
* Used in task_struct and signal_struct
*/
struct posix_cputimers {
struct posix_cputimer_base bases[CPUCLOCK_MAX];
unsigned int timers_active;
unsigned int expiry_active;
};
static inline void posix_cputimers_init(struct posix_cputimers *pct)
{
pct->timers_active = 0;
pct->expiry_active = 0;
pct->bases[0].nextevt = U64_MAX;
pct->bases[1].nextevt = U64_MAX;
pct->bases[2].nextevt = U64_MAX;

9
include/linux/sched/cputime.h
View File

@ -70,7 +70,7 @@ void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples);
*/
/**
* get_running_cputimer - return &tsk->signal->cputimer if cputimer is running
* get_running_cputimer - return &tsk->signal->cputimer if cputimers are active
*
* @tsk: Pointer to target task.
*/
@ -80,8 +80,11 @@ struct thread_group_cputimer *get_running_cputimer(struct task_struct *tsk)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
/* Check if cputimer isn't running. This is accessed without locking. */
if (!READ_ONCE(cputimer->running))
/*
* Check whether posix CPU timers are active. If not the thread
* group accounting is not active either. Lockless check.
*/
if (!READ_ONCE(tsk->signal->posix_cputimers.timers_active))
return NULL;
/*

6
include/linux/sched/signal.h
View File

@ -57,18 +57,12 @@ struct task_cputime_atomic {
/**
* struct thread_group_cputimer - thread group interval timer counts
* @cputime_atomic: atomic thread group interval timers.
* @running: true when there are timers running and
* @cputime_atomic receives updates.
* @checking_timer: true when a thread in the group is in the
* process of checking for thread group timers.
*
* This structure contains the version of task_cputime, above, that is
* used for thread group CPU timer calculations.
*/
struct thread_group_cputimer {
struct task_cputime_atomic cputime_atomic;
bool running;
bool checking_timer;
};
struct multiprocess_signals {

2
init/init_task.c
View File

@ -30,8 +30,6 @@ static struct signal_struct init_signals = {
.posix_timers = LIST_HEAD_INIT(init_signals.posix_timers),
.cputimer = {
.cputime_atomic = INIT_CPUTIME_ATOMIC,
.running = false,
.checking_timer = false,
},
#endif
INIT_CPU_TIMERS(init_signals)

6
kernel/fork.c
View File

@ -1517,7 +1517,6 @@ void __cleanup_sighand(struct sighand_struct *sighand)
}
}
#ifdef CONFIG_POSIX_TIMERS
/*
* Initialize POSIX timer handling for a thread group.
*/
@ -1528,12 +1527,7 @@ static void posix_cpu_timers_init_group(struct signal_struct *sig)
cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
posix_cputimers_group_init(pct, cpu_limit);
if (cpu_limit != RLIM_INFINITY)
sig->cputimer.running = true;
}
#else
static inline void posix_cpu_timers_init_group(struct signal_struct *sig) { }
#endif
static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
{

73
kernel/time/posix-cpu-timers.c
View File

@ -23,8 +23,10 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer);
void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
{
posix_cputimers_init(pct);
if (cpu_limit != RLIM_INFINITY)
if (cpu_limit != RLIM_INFINITY) {
pct->bases[CPUCLOCK_PROF].nextevt = cpu_limit * NSEC_PER_SEC;
pct->timers_active = true;
}
}
/*
@ -248,8 +250,9 @@ static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic,
void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
WARN_ON_ONCE(!cputimer->running);
WARN_ON_ONCE(!pct->timers_active);
proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
}
@ -269,9 +272,10 @@ void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples)
static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
/* Check if cputimer isn't running. This is accessed without locking. */
if (!READ_ONCE(cputimer->running)) {
if (!READ_ONCE(pct->timers_active)) {
struct task_cputime sum;
/*
@ -283,13 +287,13 @@ static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)
update_gt_cputime(&cputimer->cputime_atomic, &sum);
/*
* We're setting cputimer->running without a lock. Ensure
* this only gets written to in one operation. We set
* running after update_gt_cputime() as a small optimization,
* but barriers are not required because update_gt_cputime()
* We're setting timers_active without a lock. Ensure this
* only gets written to in one operation. We set it after
* update_gt_cputime() as a small optimization, but
* barriers are not required because update_gt_cputime()
* can handle concurrent updates.
*/
WRITE_ONCE(cputimer->running, true);
WRITE_ONCE(pct->timers_active, true);
}
proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
}
@ -313,9 +317,10 @@ static u64 cpu_clock_sample_group(const clockid_t clkid, struct task_struct *p,
bool start)
{
struct thread_group_cputimer *cputimer = &p->signal->cputimer;
struct posix_cputimers *pct = &p->signal->posix_cputimers;
u64 samples[CPUCLOCK_MAX];
if (!READ_ONCE(cputimer->running)) {
if (!READ_ONCE(pct->timers_active)) {
if (start)
thread_group_start_cputime(p, samples);
else
@ -834,10 +839,10 @@ static void check_thread_timers(struct task_struct *tsk,
static inline void stop_process_timers(struct signal_struct *sig)
{
struct thread_group_cputimer *cputimer = &sig->cputimer;
struct posix_cputimers *pct = &sig->posix_cputimers;
/* Turn off cputimer->running. This is done without locking. */
WRITE_ONCE(cputimer->running, false);
/* Turn off the active flag. This is done without locking. */
WRITE_ONCE(pct->timers_active, false);
tick_dep_clear_signal(sig, TICK_DEP_BIT_POSIX_TIMER);
}
@ -877,17 +882,17 @@ static void check_process_timers(struct task_struct *tsk,
unsigned long soft;
/*
* If cputimer is not running, then there are no active
* process wide timers (POSIX 1.b, itimers, RLIMIT_CPU).
* If there are no active process wide timers (POSIX 1.b, itimers,
* RLIMIT_CPU) nothing to check.
*/
if (!READ_ONCE(sig->cputimer.running))
if (!READ_ONCE(pct->timers_active))
return;
/*
* Signify that a thread is checking for process timers.
* Write access to this field is protected by the sighand lock.
*/
sig->cputimer.checking_timer = true;
pct->timers_active = true;
/*
* Collect the current process totals. Group accounting is active
@ -933,7 +938,7 @@ static void check_process_timers(struct task_struct *tsk,
if (expiry_cache_is_inactive(pct))
stop_process_timers(sig);
sig->cputimer.checking_timer = false;
pct->expiry_active = false;
}
/*
@ -1027,39 +1032,41 @@ task_cputimers_expired(const u64 *sample, struct posix_cputimers *pct)
*/
static inline bool fastpath_timer_check(struct task_struct *tsk)
{
struct posix_cputimers *pct = &tsk->posix_cputimers;
struct signal_struct *sig;
if (!expiry_cache_is_inactive(&tsk->posix_cputimers)) {
if (!expiry_cache_is_inactive(pct)) {
u64 samples[CPUCLOCK_MAX];
task_sample_cputime(tsk, samples);
if (task_cputimers_expired(samples, &tsk->posix_cputimers))
if (task_cputimers_expired(samples, pct))
return true;
}
sig = tsk->signal;
pct = &sig->posix_cputimers;
/*
* Check if thread group timers expired when the cputimer is
* running and no other thread in the group is already checking
* for thread group cputimers. These fields are read without the
* sighand lock. However, this is fine because this is meant to
* be a fastpath heuristic to determine whether we should try to
* acquire the sighand lock to check/handle timers.
* Check if thread group timers expired when timers are active and
* no other thread in the group is already handling expiry for
* thread group cputimers. These fields are read without the
* sighand lock. However, this is fine because this is meant to be
* a fastpath heuristic to determine whether we should try to
* acquire the sighand lock to handle timer expiry.
*
* In the worst case scenario, if 'running' or 'checking_timer' gets
* set but the current thread doesn't see the change yet, we'll wait
* until the next thread in the group gets a scheduler interrupt to
* handle the timer. This isn't an issue in practice because these
* types of delays with signals actually getting sent are expected.
* In the worst case scenario, if concurrently timers_active is set
* or expiry_active is cleared, but the current thread doesn't see
* the change yet, the timer checks are delayed until the next
* thread in the group gets a scheduler interrupt to handle the
* timer. This isn't an issue in practice because these types of
* delays with signals actually getting sent are expected.
*/
if (READ_ONCE(sig->cputimer.running) &&
!READ_ONCE(sig->cputimer.checking_timer)) {
if (READ_ONCE(pct->timers_active) && !READ_ONCE(pct->expiry_active)) {
u64 samples[CPUCLOCK_MAX];
proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic,
samples);
if (task_cputimers_expired(samples, &sig->posix_cputimers))
if (task_cputimers_expired(samples, pct))
return true;
}