sched: SCHED_FIFO/SCHED_RR watchdog timer

Introduce a new rlimit that allows the user to set a runtime timeout on
real-time tasks their slice. Once this limit is exceeded the task will receive
SIGXCPU.

So it measures runtime since the last sleep.

Input and ideas by Thomas Gleixner and Lennart Poettering.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Lennart Poettering <mzxreary@0pointer.de>
CC: Michael Kerrisk <mtk.manpages@googlemail.com>
CC: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 29 insertions, 0 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 68c96376e84a..2c076b36c4f6 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -967,6 +967,7 @@ 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;
 
         maxfire = 20;
         tsk->it_prof_expires = cputime_zero;
@@ -1011,6 +1012,34 @@ static void check_thread_timers(struct task_struct *tsk,
                 t->firing = 1;
                 list_move_tail(&t->entry, firing);
         }
+
+        /*
+         * 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;
+
+                if (tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
+                        /*
+                         * At the hard limit, we just die.
+                         * No need to calculate anything else now.
+                         */
+                        __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
+                        return;
+                }
+                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;
+                        }
+                        __group_send_sig_info(SIGXCPU, SEND_SIG_PRIV, tsk);
+                }
+        }
 }
 
 /*