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author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2022-03-08 20:54:13 +0300 |
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committer | Paul E. McKenney <paulmck@kernel.org> | 2022-04-12 03:06:42 +0300 |
commit | 777570d9ef820e470736fa9e02b8e3e48891c050 (patch) | |
tree | 74a947bd5224c7299d7fc8e0754997a3ef20941b /kernel/rcu | |
parent | 5d90070816534882b9158f14154b7e2cdef1194a (diff) | |
download | linux-777570d9ef820e470736fa9e02b8e3e48891c050.tar.xz |
rcu-tasks: Use schedule_hrtimeout_range() to wait for grace periods
The synchronous RCU-tasks grace-period-wait primitives invoke
schedule_timeout_idle() to give readers a chance to exit their
read-side critical sections. Unfortunately, this fails during early
boot on PREEMPT_RT because PREEMPT_RT relies solely on ksoftirqd to run
timer handlers. Because ksoftirqd cannot operate until its kthreads
are spawned, there is a brief period of time following scheduler
initialization where PREEMPT_RT cannot run the timer handlers that
schedule_timeout_idle() relies on, resulting in a hang.
To avoid this boot-time hang, this commit replaces schedule_timeout_idle()
with schedule_hrtimeout(), so that the timer expires in hardirq context.
This is ensures that the timer fires even on PREEMPT_RT throughout the
irqs-enabled portions of boot as well as during runtime.
The timer is set to expire between fract and fract + HZ / 2 jiffies in
order to align with any other timers that might expire during that time,
thus reducing the number of wakeups.
Note that RCU-tasks grace periods are infrequent, so the use of hrtimer
should be fine. In contrast, in common-case code, user of hrtimer
could result in performance issues.
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
-rw-r--r-- | kernel/rcu/tasks.h | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 4b91cb214ca7..71fe340ab82a 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -647,13 +647,16 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) fract = rtp->init_fract; while (!list_empty(&holdouts)) { + ktime_t exp; bool firstreport; bool needreport; int rtst; // Slowly back off waiting for holdouts set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS); - schedule_timeout_idle(fract); + exp = jiffies_to_nsecs(fract); + __set_current_state(TASK_IDLE); + schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD); if (fract < HZ) fract++; |