diff options
| -rw-r--r-- | include/linux/init_task.h | 1 | ||||
| -rw-r--r-- | include/linux/sched.h | 3 | ||||
| -rw-r--r-- | kernel/time/posix-cpu-timers.c | 26 |
3 files changed, 28 insertions, 2 deletions
diff --git a/include/linux/init_task.h b/include/linux/init_task.h index c43b80f3f875..810a34f60424 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -60,6 +60,7 @@ extern struct fs_struct init_fs; .cputimer = { \ .cputime_atomic = INIT_CPUTIME_ATOMIC, \ .running = false, \ + .checking_timer = false, \ }, \ INIT_PREV_CPUTIME(sig) \ .cred_guard_mutex = \ diff --git a/include/linux/sched.h b/include/linux/sched.h index 6c8504ade2ba..f87559df5b75 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -619,6 +619,8 @@ struct task_cputime_atomic { * @cputime_atomic: atomic thread group interval timers. * @running: true when there are timers running and * @cputime_atomic receives updates. + * @checking_timer: true when a thread in the group is in the + * process of checking for thread group timers. * * This structure contains the version of task_cputime, above, that is * used for thread group CPU timer calculations. @@ -626,6 +628,7 @@ struct task_cputime_atomic { struct thread_group_cputimer { struct task_cputime_atomic cputime_atomic; bool running; + bool checking_timer; }; #include <linux/rwsem.h> diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 2d58153074d9..f5e86d282d52 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -975,6 +975,12 @@ static void check_process_timers(struct task_struct *tsk, 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. */ @@ -1029,6 +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; } /* @@ -1142,8 +1150,22 @@ static inline int fastpath_timer_check(struct task_struct *tsk) } 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); |