1 files changed, 131 insertions, 215 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 438ff4523513..9829646d399c 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -11,19 +11,18 @@
 #include <trace/events/timer.h>
 
 /*
- * Called after updating RLIMIT_CPU to set timer expiration if necessary.
+ * Called after updating RLIMIT_CPU to run cpu timer and update
+ * tsk->signal->cputime_expires expiration cache if necessary. Needs
+ * siglock protection since other code may update expiration cache as
+ * well.
  */
 void update_rlimit_cpu(unsigned long rlim_new)
 {
         cputime_t cputime = secs_to_cputime(rlim_new);
-        struct signal_struct *const sig = current->signal;
 
-        if (cputime_eq(sig->it[CPUCLOCK_PROF].expires, cputime_zero) ||
-            cputime_gt(sig->it[CPUCLOCK_PROF].expires, cputime)) {
-                spin_lock_irq(&current->sighand->siglock);
-                set_process_cpu_timer(current, CPUCLOCK_PROF, &cputime, NULL);
-                spin_unlock_irq(&current->sighand->siglock);
-        }
+        spin_lock_irq(&current->sighand->siglock);
+        set_process_cpu_timer(current, CPUCLOCK_PROF, &cputime, NULL);
+        spin_unlock_irq(&current->sighand->siglock);
 }
 
 static int check_clock(const clockid_t which_clock)
@@ -364,7 +363,7 @@ int posix_cpu_clock_get(const clockid_t which_clock, struct timespec *tp)
                                 }
                         } else {
                                 read_lock(&tasklist_lock);
-                                if (thread_group_leader(p) && p->signal) {
+                                if (thread_group_leader(p) && p->sighand) {
                                         error =
                                             cpu_clock_sample_group(which_clock,
                                                                    p, &rtn);
@@ -440,7 +439,7 @@ int posix_cpu_timer_del(struct k_itimer *timer)
 
         if (likely(p != NULL)) {
                 read_lock(&tasklist_lock);
-                if (unlikely(p->signal == NULL)) {
+                if (unlikely(p->sighand == NULL)) {
                         /*
                          * We raced with the reaping of the task.
                          * The deletion should have cleared us off the list.
@@ -548,111 +547,62 @@ static inline int expires_gt(cputime_t expires, cputime_t new_exp)
                cputime_gt(expires, new_exp);
 }
 
-static inline int expires_le(cputime_t expires, cputime_t new_exp)
-{
-        return !cputime_eq(expires, cputime_zero) &&
-               cputime_le(expires, new_exp);
-}
 /*
  * Insert the timer on the appropriate list before any timers that
  * expire later.  This must be called with the tasklist_lock held
- * for reading, and interrupts disabled.
+ * for reading, interrupts disabled and p->sighand->siglock taken.
  */
-static void arm_timer(struct k_itimer *timer, union cpu_time_count now)
+static void arm_timer(struct k_itimer *timer)
 {
         struct task_struct *p = timer->it.cpu.task;
         struct list_head *head, *listpos;
+        struct task_cputime *cputime_expires;
         struct cpu_timer_list *const nt = &timer->it.cpu;
         struct cpu_timer_list *next;
-        unsigned long i;
 
-        head = (CPUCLOCK_PERTHREAD(timer->it_clock) ?
-                p->cpu_timers : p->signal->cpu_timers);
+        if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
+                head = p->cpu_timers;
+                cputime_expires = &p->cputime_expires;
+        } else {
+                head = p->signal->cpu_timers;
+                cputime_expires = &p->signal->cputime_expires;
+        }
         head += CPUCLOCK_WHICH(timer->it_clock);
 
-        BUG_ON(!irqs_disabled());
-        spin_lock(&p->sighand->siglock);
-
         listpos = head;
-        if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
-                list_for_each_entry(next, head, entry) {
-                        if (next->expires.sched > nt->expires.sched)
-                                break;
-                        listpos = &next->entry;
-                }
-        } else {
-                list_for_each_entry(next, head, entry) {
-                        if (cputime_gt(next->expires.cpu, nt->expires.cpu))
-                                break;
-                        listpos = &next->entry;
-                }
+        list_for_each_entry(next, head, entry) {
+                if (cpu_time_before(timer->it_clock, nt->expires, next->expires))
+                        break;
+                listpos = &next->entry;
         }
         list_add(&nt->entry, listpos);
 
         if (listpos == head) {
+                union cpu_time_count *exp = &nt->expires;
+
                 /*
-                 * We are the new earliest-expiring timer.
-                 * If we are a thread timer, there can always
-                 * be a process timer telling us to stop earlier.
+                 * We are the new earliest-expiring POSIX 1.b timer, hence
+                 * need to update expiration cache. Take into account that
+                 * for process timers we share expiration cache with itimers
+                 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
                  */
 
-                if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
-                        union cpu_time_count *exp = &nt->expires;
-
-                        switch (CPUCLOCK_WHICH(timer->it_clock)) {
-                        default:
-                                BUG();
-                        case CPUCLOCK_PROF:
-                                if (expires_gt(p->cputime_expires.prof_exp,
-                                               exp->cpu))
-                                        p->cputime_expires.prof_exp = exp->cpu;
-                                break;
-                        case CPUCLOCK_VIRT:
-                                if (expires_gt(p->cputime_expires.virt_exp,
-                                               exp->cpu))
-                                        p->cputime_expires.virt_exp = exp->cpu;
-                                break;
-                        case CPUCLOCK_SCHED:
-                                if (p->cputime_expires.sched_exp == 0 ||
-                                    p->cputime_expires.sched_exp > exp->sched)
-                                        p->cputime_expires.sched_exp =
-                                                                exp->sched;
-                                break;
-                        }
-                } else {
-                        struct signal_struct *const sig = p->signal;
-                        union cpu_time_count *exp = &timer->it.cpu.expires;
-
-                        /*
-                         * For a process timer, set the cached expiration time.
-                         */
-                        switch (CPUCLOCK_WHICH(timer->it_clock)) {
-                        default:
-                                BUG();
-                        case CPUCLOCK_VIRT:
-                                if (expires_le(sig->it[CPUCLOCK_VIRT].expires,
-                                               exp->cpu))
-                                        break;
-                                sig->cputime_expires.virt_exp = exp->cpu;
-                                break;
-                        case CPUCLOCK_PROF:
-                                if (expires_le(sig->it[CPUCLOCK_PROF].expires,
-                                               exp->cpu))
-                                        break;
-                                i = sig->rlim[RLIMIT_CPU].rlim_cur;
-                                if (i != RLIM_INFINITY &&
-                                    i <= cputime_to_secs(exp->cpu))
-                                        break;
-                                sig->cputime_expires.prof_exp = exp->cpu;
-                                break;
-                        case CPUCLOCK_SCHED:
-                                sig->cputime_expires.sched_exp = exp->sched;
-                                break;
-                        }
+                switch (CPUCLOCK_WHICH(timer->it_clock)) {
+                case CPUCLOCK_PROF:
+                        if (expires_gt(cputime_expires->prof_exp, exp->cpu))
+                                cputime_expires->prof_exp = exp->cpu;
+                        break;
+                case CPUCLOCK_VIRT:
+                        if (expires_gt(cputime_expires->virt_exp, exp->cpu))
+                                cputime_expires->virt_exp = exp->cpu;
+                        break;
+                case CPUCLOCK_SCHED:
+                        if (cputime_expires->sched_exp == 0 ||
+                            cputime_expires->sched_exp > exp->sched)
+                                cputime_expires->sched_exp = exp->sched;
+                        break;
                 }
         }
-
-        spin_unlock(&p->sighand->siglock);
 }
 
 /*
@@ -660,7 +610,12 @@ static void arm_timer(struct k_itimer *timer, union cpu_time_count now)
  */
 static void cpu_timer_fire(struct k_itimer *timer)
 {
-        if (unlikely(timer->sigq == NULL)) {
+        if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
+                /*
+                 * User don't want any signal.
+                 */
+                timer->it.cpu.expires.sched = 0;
+        } else if (unlikely(timer->sigq == NULL)) {
                 /*
                  * This a special case for clock_nanosleep,
                  * not a normal timer from sys_timer_create.
@@ -721,7 +676,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
                         struct itimerspec *new, struct itimerspec *old)
 {
         struct task_struct *p = timer->it.cpu.task;
-        union cpu_time_count old_expires, new_expires, val;
+        union cpu_time_count old_expires, new_expires, old_incr, val;
         int ret;
 
         if (unlikely(p == NULL)) {
@@ -736,10 +691,10 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
         read_lock(&tasklist_lock);
         /*
          * We need the tasklist_lock to protect against reaping that
-         * clears p->signal.  If p has just been reaped, we can no
+         * clears p->sighand.  If p has just been reaped, we can no
          * longer get any information about it at all.
          */
-        if (unlikely(p->signal == NULL)) {
+        if (unlikely(p->sighand == NULL)) {
                 read_unlock(&tasklist_lock);
                 put_task_struct(p);
                 timer->it.cpu.task = NULL;
@@ -752,6 +707,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
         BUG_ON(!irqs_disabled());
 
         ret = 0;
+        old_incr = timer->it.cpu.incr;
         spin_lock(&p->sighand->siglock);
         old_expires = timer->it.cpu.expires;
         if (unlikely(timer->it.cpu.firing)) {
@@ -759,7 +715,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
                 ret = TIMER_RETRY;
         } else
                 list_del_init(&timer->it.cpu.entry);
-        spin_unlock(&p->sighand->siglock);
 
         /*
          * We need to sample the current value to convert the new
@@ -813,6 +768,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
                  * disable this firing since we are already reporting
                  * it as an overrun (thanks to bump_cpu_timer above).
                  */
+                spin_unlock(&p->sighand->siglock);
                 read_unlock(&tasklist_lock);
                 goto out;
         }
@@ -828,11 +784,11 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
          */
         timer->it.cpu.expires = new_expires;
         if (new_expires.sched != 0 &&
-            (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&
             cpu_time_before(timer->it_clock, val, new_expires)) {
-                arm_timer(timer, val);
+                arm_timer(timer);
         }
 
+        spin_unlock(&p->sighand->siglock);
         read_unlock(&tasklist_lock);
 
         /*
@@ -853,7 +809,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
         timer->it_overrun = -1;
 
         if (new_expires.sched != 0 &&
-            (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&
             !cpu_time_before(timer->it_clock, val, new_expires)) {
                 /*
                  * The designated time already passed, so we notify
@@ -867,7 +822,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags,
  out:
         if (old) {
                 sample_to_timespec(timer->it_clock,
-                                   timer->it.cpu.incr, &old->it_interval);
+                                   old_incr, &old->it_interval);
         }
         return ret;
 }
@@ -908,7 +863,7 @@ void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
                 clear_dead = p->exit_state;
         } else {
                 read_lock(&tasklist_lock);
-                if (unlikely(p->signal == NULL)) {
+                if (unlikely(p->sighand == NULL)) {
                         /*
                          * The process has been reaped.
                          * We can't even collect a sample any more.
@@ -927,25 +882,6 @@ void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
                 read_unlock(&tasklist_lock);
         }
 
-        if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
-                if (timer->it.cpu.incr.sched == 0 &&
-                    cpu_time_before(timer->it_clock,
-                                    timer->it.cpu.expires, now)) {
-                        /*
-                         * Do-nothing timer expired and has no reload,
-                         * so it's as if it was never set.
-                         */
-                        timer->it.cpu.expires.sched = 0;
-                        itp->it_value.tv_sec = itp->it_value.tv_nsec = 0;
-                        return;
-                }
-                /*
-                 * Account for any expirations and reloads that should
-                 * have happened.
-                 */
-                bump_cpu_timer(timer, now);
-        }
-
         if (unlikely(clear_dead)) {
                 /*
                  * We've noticed that the thread is dead, but
@@ -982,6 +918,7 @@ static void check_thread_timers(struct task_struct *tsk,
         int maxfire;
         struct list_head *timers = tsk->cpu_timers;
         struct signal_struct *const sig = tsk->signal;
+        unsigned long soft;
 
         maxfire = 20;
         tsk->cputime_expires.prof_exp = cputime_zero;
@@ -1030,9 +967,10 @@ static void check_thread_timers(struct task_struct *tsk,
         /*
          * Check for the special case thread timers.
          */
-        if (sig->rlim[RLIMIT_RTTIME].rlim_cur != RLIM_INFINITY) {
-                unsigned long hard = sig->rlim[RLIMIT_RTTIME].rlim_max;
-                unsigned long *soft = &sig->rlim[RLIMIT_RTTIME].rlim_cur;
+        soft = ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_cur);
+        if (soft != RLIM_INFINITY) {
+                unsigned long hard =
+                        ACCESS_ONCE(sig->rlim[RLIMIT_RTTIME].rlim_max);
 
                 if (hard != RLIM_INFINITY &&
                     tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
@@ -1043,14 +981,13 @@ static void check_thread_timers(struct task_struct *tsk,
                         __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
                         return;
                 }
-                if (tsk->rt.timeout > DIV_ROUND_UP(*soft, USEC_PER_SEC/HZ)) {
+                if (tsk->rt.timeout > DIV_ROUND_UP(soft, USEC_PER_SEC/HZ)) {
                         /*
                          * At the soft limit, send a SIGXCPU every second.
                          */
-                        if (sig->rlim[RLIMIT_RTTIME].rlim_cur
-                            < sig->rlim[RLIMIT_RTTIME].rlim_max) {
-                                sig->rlim[RLIMIT_RTTIME].rlim_cur +=
-                                                                USEC_PER_SEC;
+                        if (soft < hard) {
+                                soft += USEC_PER_SEC;
+                                sig->rlim[RLIMIT_RTTIME].rlim_cur = soft;
                         }
                         printk(KERN_INFO
                                 "RT Watchdog Timeout: %s[%d]\n",
@@ -1060,14 +997,11 @@ static void check_thread_timers(struct task_struct *tsk,
         }
 }
 
-static void stop_process_timers(struct task_struct *tsk)
+static void stop_process_timers(struct signal_struct *sig)
 {
-        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+        struct thread_group_cputimer *cputimer = &sig->cputimer;
         unsigned long flags;
 
-        if (!cputimer->running)
-                return;
-
         spin_lock_irqsave(&cputimer->lock, flags);
         cputimer->running = 0;
         spin_unlock_irqrestore(&cputimer->lock, flags);
@@ -1107,6 +1041,23 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
         }
 }
 
+/**
+ * task_cputime_zero - Check a task_cputime struct for all zero fields.
+ *
+ * @cputime:    The struct to compare.
+ *
+ * Checks @cputime to see if all fields are zero.  Returns true if all fields
+ * are zero, false if any field is nonzero.
+ */
+static inline int task_cputime_zero(const struct task_cputime *cputime)
+{
+        if (cputime_eq(cputime->utime, cputime_zero) &&
+            cputime_eq(cputime->stime, cputime_zero) &&
+            cputime->sum_exec_runtime == 0)
+                return 1;
+        return 0;
+}
+
 /*
  * Check for any per-thread CPU timers that have fired and move them
  * off the tsk->*_timers list onto the firing list.  Per-thread timers
@@ -1121,19 +1072,7 @@ static void check_process_timers(struct task_struct *tsk,
         unsigned long long sum_sched_runtime, sched_expires;
         struct list_head *timers = sig->cpu_timers;
         struct task_cputime cputime;
-
-        /*
-         * Don't sample the current process CPU clocks if there are no timers.
-         */
-        if (list_empty(&timers[CPUCLOCK_PROF]) &&
-            cputime_eq(sig->it[CPUCLOCK_PROF].expires, cputime_zero) &&
-            sig->rlim[RLIMIT_CPU].rlim_cur == RLIM_INFINITY &&
-            list_empty(&timers[CPUCLOCK_VIRT]) &&
-            cputime_eq(sig->it[CPUCLOCK_VIRT].expires, cputime_zero) &&
-            list_empty(&timers[CPUCLOCK_SCHED])) {
-                stop_process_timers(tsk);
-                return;
-        }
+        unsigned long soft;
 
         /*
          * Collect the current process totals.
@@ -1193,11 +1132,13 @@ static void check_process_timers(struct task_struct *tsk,
                          SIGPROF);
         check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
                          SIGVTALRM);
-
-        if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
+        soft = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
+        if (soft != RLIM_INFINITY) {
                 unsigned long psecs = cputime_to_secs(ptime);
+                unsigned long hard =
+                        ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_max);
                 cputime_t x;
-                if (psecs >= sig->rlim[RLIMIT_CPU].rlim_max) {
+                if (psecs >= hard) {
                         /*
                          * At the hard limit, we just die.
                          * No need to calculate anything else now.
@@ -1205,35 +1146,28 @@ static void check_process_timers(struct task_struct *tsk,
                         __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
                         return;
                 }
-                if (psecs >= sig->rlim[RLIMIT_CPU].rlim_cur) {
+                if (psecs >= soft) {
                         /*
                          * At the soft limit, send a SIGXCPU every second.
                          */
                         __group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
-                        if (sig->rlim[RLIMIT_CPU].rlim_cur
-                            < sig->rlim[RLIMIT_CPU].rlim_max) {
-                                sig->rlim[RLIMIT_CPU].rlim_cur++;
+                        if (soft < hard) {
+                                soft++;
+                                sig->rlim[RLIMIT_CPU].rlim_cur = soft;
                         }
                 }
-                x = secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
+                x = secs_to_cputime(soft);
                 if (cputime_eq(prof_expires, cputime_zero) ||
                     cputime_lt(x, prof_expires)) {
                         prof_expires = x;
                 }
         }
 
-        if (!cputime_eq(prof_expires, cputime_zero) &&
-            (cputime_eq(sig->cputime_expires.prof_exp, cputime_zero) ||
-             cputime_gt(sig->cputime_expires.prof_exp, prof_expires)))
-                sig->cputime_expires.prof_exp = prof_expires;
-        if (!cputime_eq(virt_expires, cputime_zero) &&
-            (cputime_eq(sig->cputime_expires.virt_exp, cputime_zero) ||
-             cputime_gt(sig->cputime_expires.virt_exp, virt_expires)))
-                sig->cputime_expires.virt_exp = virt_expires;
-        if (sched_expires != 0 &&
-            (sig->cputime_expires.sched_exp == 0 ||
-             sig->cputime_expires.sched_exp > sched_expires))
-                sig->cputime_expires.sched_exp = sched_expires;
+        sig->cputime_expires.prof_exp = prof_expires;
+        sig->cputime_expires.virt_exp = virt_expires;
+        sig->cputime_expires.sched_exp = sched_expires;
+        if (task_cputime_zero(&sig->cputime_expires))
+                stop_process_timers(sig);
 }
 
 /*
@@ -1262,9 +1196,10 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
                         goto out;
                 }
                 read_lock(&tasklist_lock); /* arm_timer needs it.  */
+                spin_lock(&p->sighand->siglock);
         } else {
                 read_lock(&tasklist_lock);
-                if (unlikely(p->signal == NULL)) {
+                if (unlikely(p->sighand == NULL)) {
                         /*
                          * The process has been reaped.
                          * We can't even collect a sample any more.
@@ -1282,6 +1217,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
                         clear_dead_task(timer, now);
                         goto out_unlock;
                 }
+                spin_lock(&p->sighand->siglock);
                 cpu_timer_sample_group(timer->it_clock, p, &now);
                 bump_cpu_timer(timer, now);
                 /* Leave the tasklist_lock locked for the call below.  */
@@ -1290,7 +1226,9 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
         /*
          * Now re-arm for the new expiry time.
          */
-        arm_timer(timer, now);
+        BUG_ON(!irqs_disabled());
+        arm_timer(timer);
+        spin_unlock(&p->sighand->siglock);
 
 out_unlock:
         read_unlock(&tasklist_lock);
@@ -1302,23 +1240,6 @@ out:
 }
 
 /**
- * task_cputime_zero - Check a task_cputime struct for all zero fields.
- *
- * @cputime:    The struct to compare.
- *
- * Checks @cputime to see if all fields are zero.  Returns true if all fields
- * are zero, false if any field is nonzero.
- */
-static inline int task_cputime_zero(const struct task_cputime *cputime)
-{
-        if (cputime_eq(cputime->utime, cputime_zero) &&
-            cputime_eq(cputime->stime, cputime_zero) &&
-            cputime->sum_exec_runtime == 0)
-                return 1;
-        return 0;
-}
-
-/**
  * task_cputime_expired - Compare two task_cputime entities.
  *
  * @sample:     The task_cputime structure to be checked for expiration.
@@ -1374,7 +1295,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
         }
 
         sig = tsk->signal;
-        if (!task_cputime_zero(&sig->cputime_expires)) {
+        if (sig->cputimer.running) {
                 struct task_cputime group_sample;
 
                 thread_group_cputimer(tsk, &group_sample);
@@ -1382,7 +1303,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
                         return 1;
         }
 
-        return sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY;
+        return 0;
 }
 
 /*
@@ -1411,7 +1332,12 @@ void run_posix_cpu_timers(struct task_struct *tsk)
          * put them on the firing list.
          */
         check_thread_timers(tsk, &firing);
-        check_process_timers(tsk, &firing);
+        /*
+         * If there are any active process wide timers (POSIX 1.b, itimers,
+         * RLIMIT_CPU) cputimer must be running.
+         */
+        if (tsk->signal->cputimer.running)
+                check_process_timers(tsk, &firing);
 
         /*
          * We must release these locks before taking any timer's lock.
@@ -1448,21 +1374,23 @@ void run_posix_cpu_timers(struct task_struct *tsk)
 }
 
 /*
- * Set one of the process-wide special case CPU timers.
+ * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
  * The tsk->sighand->siglock must be held by the caller.
- * The *newval argument is relative and we update it to be absolute, *oldval
- * is absolute and we update it to be relative.
  */
 void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
                            cputime_t *newval, cputime_t *oldval)
 {
         union cpu_time_count now;
-        struct list_head *head;
 
         BUG_ON(clock_idx == CPUCLOCK_SCHED);
         cpu_timer_sample_group(clock_idx, tsk, &now);
 
         if (oldval) {
+                /*
+                 * We are setting itimer. The *oldval is absolute and we update
+                 * it to be relative, *newval argument is relative and we update
+                 * it to be absolute.
+                 */
                 if (!cputime_eq(*oldval, cputime_zero)) {
                         if (cputime_le(*oldval, now.cpu)) {
                                 /* Just about to fire. */
@@ -1475,33 +1403,21 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
                 if (cputime_eq(*newval, cputime_zero))
                         return;
                 *newval = cputime_add(*newval, now.cpu);
-
-                /*
-                 * If the RLIMIT_CPU timer will expire before the
-                 * ITIMER_PROF timer, we have nothing else to do.
-                 */
-                if (tsk->signal->rlim[RLIMIT_CPU].rlim_cur
-                    < cputime_to_secs(*newval))
-                        return;
         }
 
         /*
-         * Check whether there are any process timers already set to fire
-         * before this one.  If so, we don't have anything more to do.
+         * Update expiration cache if we are the earliest timer, or eventually
+         * RLIMIT_CPU limit is earlier than prof_exp cpu timer expire.
          */
-        head = &tsk->signal->cpu_timers[clock_idx];
-        if (list_empty(head) ||
-            cputime_ge(list_first_entry(head,
-                                  struct cpu_timer_list, entry)->expires.cpu,
-                       *newval)) {
-                switch (clock_idx) {
-                case CPUCLOCK_PROF:
+        switch (clock_idx) {
+        case CPUCLOCK_PROF:
+                if (expires_gt(tsk->signal->cputime_expires.prof_exp, *newval))
                         tsk->signal->cputime_expires.prof_exp = *newval;
-                        break;
-                case CPUCLOCK_VIRT:
+                break;
+        case CPUCLOCK_VIRT:
+                if (expires_gt(tsk->signal->cputime_expires.virt_exp, *newval))
                         tsk->signal->cputime_expires.virt_exp = *newval;
-                        break;
-                }
+                break;
         }
 }