On Sat, 2016-02-13 at 00:02 +0100, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>
> We currently disable migration across lock acquisition. That includes the part
> where we block on the lock and schedule out. We cannot disable migration after
> taking the lock as that would cause a possible lock inversion.
>
> But we can be smart and enable migration when we block and schedule out. That
> allows the scheduler to place the task freely at least if this is the first
> migrate disable level. For nested locking this does not help at all.
I met a problem while testing shiny new hotplug machinery.
rt/locking: Fix rt_spin_lock_slowlock() vs hotplug migrate_disable() bug
migrate_disable() -> pin_current_cpu() -> hotplug_lock() leads to..
BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on));
..so let's call migrate_disable() after we acquire the lock instead.
Fixes: e24b142cfb4a rt/locking: Reenable migration accross schedule
Signed-off-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxxx>
---
kernel/locking/rtmutex.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1011,7 +1011,7 @@ static void noinline __sched rt_spin_lo
struct task_struct *lock_owner, *self = current;
struct rt_mutex_waiter waiter, *top_waiter;
unsigned long flags;
- int ret;
+ bool mg_disable = false;
rt_mutex_init_waiter(&waiter, true);
@@ -1035,8 +1035,7 @@ static void noinline __sched rt_spin_lo
__set_current_state_no_track(TASK_UNINTERRUPTIBLE);
raw_spin_unlock(&self->pi_lock);
- ret = task_blocks_on_rt_mutex(lock, &waiter, self, RT_MUTEX_MIN_CHAINWALK);
- BUG_ON(ret);
+ BUG_ON(task_blocks_on_rt_mutex(lock, &waiter, self, RT_MUTEX_MIN_CHAINWALK));
for (;;) {
/* Try to acquire the lock again. */
@@ -1051,11 +1050,12 @@ static void noinline __sched rt_spin_lo
debug_rt_mutex_print_deadlock(&waiter);
if (top_waiter != &waiter || adaptive_wait(lock, lock_owner)) {
- if (mg_off)
+ if (mg_off && self->migrate_disable == 1) {
+ mg_off = false;
+ mg_disable = true;
migrate_enable();
+ }
schedule();
- if (mg_off)
- migrate_disable();
}
raw_spin_lock_irqsave(&lock->wait_lock, flags);
@@ -1088,6 +1088,9 @@ static void noinline __sched rt_spin_lo
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+ if (mg_disable)
+ migrate_disable();
+
debug_rt_mutex_free_waiter(&waiter);
}
--
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