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: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192922.275086128@linutronix.de

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 64bd10d251fe883c3e51a2310cfecdfbdaab5c5f..3ea920e8fe7f299091d584ee29a77e8b278ab501 100644 (file)
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -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);
@@ -102,7 +104,8 @@ static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
 
 /* Init task static initializer */
 #define INIT_CPU_TIMERBASE(b) {                                                \
-       .cpu_timers = LIST_HEAD_INIT(b.cpu_timers),                     \
+       .nextevt        = U64_MAX,                                      \
+       .cpu_timers     = LIST_HEAD_INIT(b.cpu_timers),                 \
 }
 
 #define INIT_CPU_TIMERBASES(b) {                                       \

diff --git a/kernel/sys.c b/kernel/sys.c
index c578b75d79237c780642c0aaa72b4c05edbcf9f9..2462aa84247fc9afea9b56c25331d84c1953bc1e 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -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)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index a738d7659915e2d44552c0d6e637ef8f267c745f..cf85292575c59ec48afe65a3b115591699e26a16 100644 (file)
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -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);