Commit 2bbdbdae authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

posix-cpu-timers: Get rid of zero checks 



Deactivation of the expiry cache is done by setting all clock caches to
0. That requires to have a check for zero in all places which update the
expiry cache:

	if (cache == 0 || new < cache)
		cache = new;

Use U64_MAX as the deactivated value, which allows to remove the zero
checks when updating the cache and reduces it to the obvious check:

	if (new < cache)
		cache = new;

This also removes the weird workaround in do_prlimit() which was required
to convert a RLIMIT_CPU value of 0 (immediate expiry) to 1 because handing
in 0 to the posix CPU timer code would have effectively disarmed it.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192922.275086128@linutronix.de
parent 24db4dd9

include/linux/posix-timers.h

+5 −2
Original line number Diff line number Diff line
@@ -86,7 +86,9 @@ struct posix_cputimers { 


static inline void posix_cputimers_init(struct posix_cputimers *pct)

{

	memset(pct->bases, 0, sizeof(pct->bases));

	pct->bases[0].nextevt = U64_MAX;

	pct->bases[1].nextevt = U64_MAX;

	pct->bases[2].nextevt = U64_MAX;

	INIT_LIST_HEAD(&pct->bases[0].cpu_timers);

	INIT_LIST_HEAD(&pct->bases[1].cpu_timers);

	INIT_LIST_HEAD(&pct->bases[2].cpu_timers);
@@ -102,6 +104,7 @@ static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct, 


/* Init task static initializer */

#define INIT_CPU_TIMERBASE(b) {						\

	.nextevt	= U64_MAX,					\

	.cpu_timers	= LIST_HEAD_INIT(b.cpu_timers),			\

}

kernel/sys.c

+0 −9
Original line number Diff line number Diff line
@@ -1557,15 +1557,6 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource, 
			retval = -EPERM;

		if (!retval)

			retval = security_task_setrlimit(tsk, resource, new_rlim);

		if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {

			/*

			 * The caller is asking for an immediate RLIMIT_CPU

			 * expiry.  But we use the zero value to mean "it was

			 * never set".  So let's cheat and make it one second

			 * instead

			 */

			new_rlim->rlim_cur = 1;

		}

	}

	if (!retval) {

		if (old_rlim)

kernel/time/posix-cpu-timers.c

+15 −23
Original line number Diff line number Diff line
@@ -122,11 +122,12 @@ static void bump_cpu_timer(struct k_itimer *timer, u64 now) 
	}

}



static inline bool expiry_cache_is_zero(const struct posix_cputimers *pct)

/* Check whether all cache entries contain U64_MAX, i.e. eternal expiry time */

static inline bool expiry_cache_is_inactive(const struct posix_cputimers *pct)

{

	return !(pct->bases[CPUCLOCK_PROF].nextevt |

		 pct->bases[CPUCLOCK_VIRT].nextevt |

		 pct->bases[CPUCLOCK_SCHED].nextevt);

	return !(~pct->bases[CPUCLOCK_PROF].nextevt |

		 ~pct->bases[CPUCLOCK_VIRT].nextevt |

		 ~pct->bases[CPUCLOCK_SCHED].nextevt);

}



static int
@@ -442,11 +443,6 @@ void posix_cpu_timers_exit_group(struct task_struct *tsk) 
	cleanup_timers(&tsk->signal->posix_cputimers);

}



static inline int expires_gt(u64 expires, u64 new_exp)

{

	return expires == 0 || expires > new_exp;

}



/*

 * Insert the timer on the appropriate list before any timers that

 * expire later.  This must be called with the sighand lock held.
@@ -483,7 +479,7 @@ static void arm_timer(struct k_itimer *timer) 
	 * for process timers we share expiration cache with itimers

	 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.

	 */

	if (expires_gt(base->nextevt, newexp))

	if (newexp < base->nextevt)

		base->nextevt = newexp;



	if (CPUCLOCK_PERTHREAD(timer->it_clock))
@@ -753,7 +749,7 @@ check_timers_list(struct list_head *timers, 
		list_move_tail(&t->entry, firing);

	}



	return 0;

	return U64_MAX;

}



static inline void check_dl_overrun(struct task_struct *tsk)
@@ -779,11 +775,7 @@ static void check_thread_timers(struct task_struct *tsk, 
	if (dl_task(tsk))

		check_dl_overrun(tsk);



	/*

	 * If the expiry cache is zero, then there are no active per thread

	 * CPU timers.

	 */

	if (expiry_cache_is_zero(&tsk->posix_cputimers))

	if (expiry_cache_is_inactive(&tsk->posix_cputimers))

		return;



	task_cputime(tsk, &utime, &stime);
@@ -833,7 +825,7 @@ static void check_thread_timers(struct task_struct *tsk, 
		}

	}



	if (expiry_cache_is_zero(&tsk->posix_cputimers))

	if (expiry_cache_is_inactive(&tsk->posix_cputimers))

		tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);

}
@@ -864,7 +856,7 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it, 
		__group_send_sig_info(signo, SEND_SIG_PRIV, tsk);

	}



	if (it->expires && (!*expires || it->expires < *expires))

	if (it->expires && it->expires < *expires)

		*expires = it->expires;

}
@@ -948,7 +940,7 @@ static void check_process_timers(struct task_struct *tsk, 
			}

		}

		softns = soft * NSEC_PER_SEC;

		if (!prof_exp || softns < prof_exp)

		if (softns < prof_exp)

			prof_exp = softns;

	}
@@ -956,7 +948,7 @@ static void check_process_timers(struct task_struct *tsk, 
	base[CPUCLOCK_VIRT].nextevt = virt_exp;

	base[CPUCLOCK_SCHED].nextevt = sched_exp;



	if (expiry_cache_is_zero(&sig->posix_cputimers))

	if (expiry_cache_is_inactive(&sig->posix_cputimers))

		stop_process_timers(sig);



	sig->cputimer.checking_timer = false;
@@ -1035,7 +1027,7 @@ task_cputimers_expired(const u64 *sample, struct posix_cputimers *pct) 
	int i;



	for (i = 0; i < CPUCLOCK_MAX; i++) {

		if (pct->bases[i].nextevt && sample[i] >= pct->bases[i].nextevt)

		if (sample[i] >= pct->bases[i].nextevt)

			return true;

	}

	return false;
@@ -1055,7 +1047,7 @@ static inline bool fastpath_timer_check(struct task_struct *tsk) 
{

	struct signal_struct *sig;



	if (!expiry_cache_is_zero(&tsk->posix_cputimers)) {

	if (!expiry_cache_is_inactive(&tsk->posix_cputimers)) {

		u64 samples[CPUCLOCK_MAX];



		task_sample_cputime(tsk, samples);
@@ -1200,7 +1192,7 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid, 
	 * Update expiration cache if this is the earliest timer. CPUCLOCK_PROF

	 * expiry cache is also used by RLIMIT_CPU!.

	 */

	if (expires_gt(*nextevt, *newval))

	if (*newval < *nextevt)

		*nextevt = *newval;



	tick_dep_set_signal(tsk->signal, TICK_DEP_BIT_POSIX_TIMER);

CRA Git | Maintained and supported by SUSTech CRA and CCSE