lkml.org 
[lkml]   [2022]   [Jul]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 2/2] sched: Consider task_struct::saved_state in wait_task_inactive().
Date
Ptrace is using wait_task_inactive() to wait for the tracee to reach a
certain task state. On PREEMPT_RT that state may be stored in
task_struct::saved_state while the tracee blocks on a sleeping lock and
task_struct::__state is set to TASK_RTLOCK_WAIT.
It is not possible to check only for TASK_RTLOCK_WAIT to be sure that the task
is blocked on a sleeping lock because during wake up (after the sleeping lock
has been acquired) the task state is set TASK_RUNNING. After the task in on CPU
and acquired the pi_lock it will reset the state accordingly but until then
TASK_RUNNING will be observed (with the desired state saved in saved_state).

Check also for task_struct::saved_state if the desired match was not found in
task_struct::__state on PREEMPT_RT. If the state was found in saved_state, wait
until the task is idle and state is visible in task_struct::__state.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/sched/core.c | 46 +++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 41 insertions(+), 5 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3257,6 +3257,40 @@ int migrate_swap(struct task_struct *cur
}
#endif /* CONFIG_NUMA_BALANCING */

+#ifdef CONFIG_PREEMPT_RT
+static __always_inline bool state_mismatch(struct task_struct *p, unsigned int match_state)
+{
+ unsigned long flags;
+ bool mismatch;
+
+ raw_spin_lock_irqsave(&p->pi_lock, flags);
+ mismatch = READ_ONCE(p->__state) != match_state &&
+ READ_ONCE(p->saved_state) != match_state;
+ raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+ return mismatch;
+}
+static __always_inline bool state_match(struct task_struct *p, unsigned int match_state,
+ bool *wait)
+{
+ if (READ_ONCE(p->__state) == match_state)
+ return true;
+ if (READ_ONCE(p->saved_state) != match_state)
+ return false;
+ *wait = true;
+ return true;
+}
+#else
+static __always_inline bool state_mismatch(struct task_struct *p, unsigned int match_state)
+{
+ return READ_ONCE(p->__state) != match_state;
+}
+static __always_inline bool state_match(struct task_struct *p, unsigned int match_state,
+ bool *wait)
+{
+ return READ_ONCE(p->__state) == match_state;
+}
+#endif
+
/*
* wait_task_inactive - wait for a thread to unschedule.
*
@@ -3275,7 +3309,7 @@ int migrate_swap(struct task_struct *cur
*/
unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
{
- int running, queued;
+ bool running, wait;
struct rq_flags rf;
unsigned long ncsw;
struct rq *rq;
@@ -3301,7 +3335,7 @@ unsigned long wait_task_inactive(struct
* is actually now running somewhere else!
*/
while (task_running(rq, p)) {
- if (match_state && unlikely(READ_ONCE(p->__state) != match_state))
+ if (match_state && state_mismatch(p, match_state))
return 0;
cpu_relax();
}
@@ -3314,10 +3348,12 @@ unsigned long wait_task_inactive(struct
rq = task_rq_lock(p, &rf);
trace_sched_wait_task(p);
running = task_running(rq, p);
- queued = task_on_rq_queued(p);
+ wait = task_on_rq_queued(p);
ncsw = 0;
- if (!match_state || READ_ONCE(p->__state) == match_state)
+
+ if (!match_state || state_match(p, match_state, &wait))
ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
+
task_rq_unlock(rq, p, &rf);

/*
@@ -3346,7 +3382,7 @@ unsigned long wait_task_inactive(struct
* running right now), it's preempted, and we should
* yield - it could be a while.
*/
- if (unlikely(queued)) {
+ if (unlikely(wait)) {
ktime_t to = NSEC_PER_SEC / HZ;

set_current_state(TASK_UNINTERRUPTIBLE);
\
 
 \ /
  Last update: 2022-07-20 17:45    [W:0.098 / U:1.540 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site