Re: [PATCH v2] futex: lower the lock contention on the HB lock during wake up

Thomas Gleixner
2015-06-19T18:55:27Z

On Fri, 19 Jun 2015, Kevin Hilman wrote:
> On Wed, Jun 17, 2015 at 1:33 AM, Sebastian Andrzej Siewior
> A handful of boot test failures on ARM/OMAP were found by kernelci.org
> in next-20150619[1] and were bisected down to this patch, which hit
> next-20150619 in the form of commit 881bd58d6e9e (futex: Lower the
> lock contention on the HB lock during wake up). I confirmed that
> reverting that patch on top of next-20150619 gets things booting again
> for the affected platforms.
>
> I haven't debugged this any further, but full boot logs are available
> for the boot failures[2][3] and the linux-omap list and maintainer are
> Cc'd here to help investigate further if needed.

Found it. Dunno, how I missed that one. Fix below.

Thanks,

tglx
---

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 10dbeb6fe96f..5674b073473c 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1365,9 +1365,14 @@ rt_mutex_fastunlock(struct rt_mutex *lock,
if (likely(rt_mutex_cmpxchg(lock, current, NULL))) {
rt_mutex_deadlock_account_unlock(current);

- } else if (slowfn(lock, &wake_q)) {
+ } else {
+ bool deboost = slowfn(lock, &wake_q);
+
+ wake_up_q(&wake_q);
+
/* Undo pi boosting if necessary: */
- rt_mutex_adjust_prio(current);
+ if (deboost)
+ rt_mutex_adjust_prio(current);
}
}

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