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-rw-r--r--kernel/time/posix-cpu-timers.c63
1 files changed, 45 insertions, 18 deletions
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 892e3dae0aac..f5e86d282d52 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -249,7 +249,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
* but barriers are not required because update_gt_cputime()
* can handle concurrent updates.
*/
- WRITE_ONCE(cputimer->running, 1);
+ WRITE_ONCE(cputimer->running, true);
}
sample_cputime_atomic(times, &cputimer->cputime_atomic);
}
@@ -864,6 +864,13 @@ static void check_thread_timers(struct task_struct *tsk,
unsigned long long expires;
unsigned long soft;
+ /*
+ * If cputime_expires is zero, then there are no active
+ * per thread CPU timers.
+ */
+ if (task_cputime_zero(&tsk->cputime_expires))
+ return;
+
expires = check_timers_list(timers, firing, prof_ticks(tsk));
tsk_expires->prof_exp = expires_to_cputime(expires);
@@ -911,7 +918,7 @@ static inline void stop_process_timers(struct signal_struct *sig)
struct thread_group_cputimer *cputimer = &sig->cputimer;
/* Turn off cputimer->running. This is done without locking. */
- WRITE_ONCE(cputimer->running, 0);
+ WRITE_ONCE(cputimer->running, false);
}
static u32 onecputick;
@@ -962,6 +969,19 @@ 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 (!READ_ONCE(tsk->signal->cputimer.running))
+ 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;
+
+ /*
* Collect the current process totals.
*/
thread_group_cputimer(tsk, &cputime);
@@ -1015,6 +1035,8 @@ static void check_process_timers(struct task_struct *tsk,
sig->cputime_expires.sched_exp = sched_expires;
if (task_cputime_zero(&sig->cputime_expires))
stop_process_timers(sig);
+
+ sig->cputimer.checking_timer = false;
}
/*
@@ -1117,24 +1139,33 @@ static inline int task_cputime_expired(const struct task_cputime *sample,
static inline int fastpath_timer_check(struct task_struct *tsk)
{
struct signal_struct *sig;
- cputime_t utime, stime;
-
- task_cputime(tsk, &utime, &stime);
if (!task_cputime_zero(&tsk->cputime_expires)) {
- struct task_cputime task_sample = {
- .utime = utime,
- .stime = stime,
- .sum_exec_runtime = tsk->se.sum_exec_runtime
- };
+ struct task_cputime task_sample;
+ task_cputime(tsk, &task_sample.utime, &task_sample.stime);
+ task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;
if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
return 1;
}
sig = tsk->signal;
- /* Check if cputimer is running. This is accessed without locking. */
- if (READ_ONCE(sig->cputimer.running)) {
+ /*
+ * 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.
+ *
+ * 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.
+ */
+ if (READ_ONCE(sig->cputimer.running) &&
+ !READ_ONCE(sig->cputimer.checking_timer)) {
struct task_cputime group_sample;
sample_cputime_atomic(&group_sample, &sig->cputimer.cputime_atomic);
@@ -1174,12 +1205,8 @@ void run_posix_cpu_timers(struct task_struct *tsk)
* put them on the firing list.
*/
check_thread_timers(tsk, &firing);
- /*
- * If there are any active process wide timers (POSIX 1.b, itimers,
- * RLIMIT_CPU) cputimer must be running.
- */
- if (READ_ONCE(tsk->signal->cputimer.running))
- check_process_timers(tsk, &firing);
+
+ check_process_timers(tsk, &firing);
/*
* We must release these locks before taking any timer's lock.