[PATCH v3 3/3] sched: Rework check_for_tasks()

Kirill Tkhai
2014-06-25T08:20:04Z

1)Iterate thru all of threads in the system.
Check for all threads, not only for group leaders.

2)Check for p->on_rq instead of p->state and cputime.
Preempted task in !TASK_RUNNING state OR just
created task may be queued, that we want to be
reported too.

3)Use read_lock() instead of write_lock().
This function does not change any structures, and
read_lock() is enough.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
CC: Konstantin Khorenko <khorenko@parallels.com>
CC: Ben Segall <bsegall@google.com>
CC: Paul Turner <pjt@google.com>
CC: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
CC: Mike Galbraith <umgwanakikbuti@gmail.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@kernel.org>
---
kernel/cpu.c | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index a343bde..81e2a38 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -274,21 +274,28 @@ void clear_tasks_mm_cpumask(int cpu)
rcu_read_unlock();
}

-static inline void check_for_tasks(int cpu)
+static inline void check_for_tasks(int dead_cpu)
{
- struct task_struct *p;
- cputime_t utime, stime;
+ struct task_struct *g, *p;

- write_lock_irq(&tasklist_lock);
- for_each_process(p) {
- task_cputime(p, &utime, &stime);
- if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
- (utime || stime))
- pr_warn("Task %s (pid = %d) is on cpu %d (state = %ld, flags = %x)\n",
- p->comm, task_pid_nr(p), cpu,
- p->state, p->flags);
- }
- write_unlock_irq(&tasklist_lock);
+ read_lock_irq(&tasklist_lock);
+ do_each_thread(g, p) {
+ if (!p->on_rq)
+ continue;
+ /*
+ * We do the check with unlocked task_rq(p)->lock.
+ * Order the reading to do not warn about a task,
+ * which was running on this cpu in the past, and
+ * it's just been woken on another cpu.
+ */
+ rmb();
+ if (task_cpu(p) != dead_cpu)
+ continue;
+
+ pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
+ p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
+ } while_each_thread(g, p);
+ read_unlock_irq(&tasklist_lock);
}

struct take_cpu_down_param {