[GIT PULL] scheduler fixes

Ingo Molnar
2020-07-25T10:47:32Z

Linus,

Please pull the latest sched/urgent git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-2020-07-25

# HEAD: 062d3f95b630113e1156a31f376ad36e25da29a7 sched: Warn if garbage is passed to default_wake_function()

Fix a race introduced by the recent loadavg race fix, plus add a
debug check for a hard to debug case of bogus wakeup function flags.

Thanks,

Ingo

------------------>
Chris Wilson (1):
sched: Warn if garbage is passed to default_wake_function()

Peter Zijlstra (1):
sched: Fix race against ptrace_freeze_trace()

kernel/sched/core.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e15543cb8481..2142c6767682 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4119,9 +4119,6 @@ static void __sched notrace __schedule(bool preempt)
local_irq_disable();
rcu_note_context_switch(preempt);

- /* See deactivate_task() below. */
- prev_state = prev->state;
-
/*
* Make sure that signal_pending_state()->signal_pending() below
* can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
@@ -4145,11 +4142,16 @@ static void __sched notrace __schedule(bool preempt)
update_rq_clock(rq);

switch_count = &prev->nivcsw;
+
/*
- * We must re-load prev->state in case ttwu_remote() changed it
- * before we acquired rq->lock.
+ * We must load prev->state once (task_struct::state is volatile), such
+ * that:
+ *
+ * - we form a control dependency vs deactivate_task() below.
+ * - ptrace_{,un}freeze_traced() can change ->state underneath us.
*/
- if (!preempt && prev_state && prev_state == prev->state) {
+ prev_state = prev->state;
+ if (!preempt && prev_state) {
if (signal_pending_state(prev_state, prev)) {
prev->state = TASK_RUNNING;
} else {
@@ -4163,10 +4165,12 @@ static void __sched notrace __schedule(bool preempt)

/*
* __schedule() ttwu()
- * prev_state = prev->state; if (READ_ONCE(p->on_rq) && ...)
- * LOCK rq->lock goto out;
- * smp_mb__after_spinlock(); smp_acquire__after_ctrl_dep();
- * p->on_rq = 0; p->state = TASK_WAKING;
+ * prev_state = prev->state; if (p->on_rq && ...)
+ * if (prev_state) goto out;
+ * p->on_rq = 0; smp_acquire__after_ctrl_dep();
+ * p->state = TASK_WAKING
+ *
+ * Where __schedule() and ttwu() have matching control dependencies.
*
* After this, schedule() must not care about p->state any more.
*/
@@ -4481,6 +4485,7 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
void *key)
{
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~WF_SYNC);
return try_to_wake_up(curr->private, mode, wake_flags);
}
EXPORT_SYMBOL(default_wake_function);