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

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Date:	Fri, 19 Jun 2015 20:54:44 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Kevin Hilman <khilman@...nel.org>
cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Tyler Baker <tyler.baker@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Tony Lindgren <tony@...mide.com>,
	linux-omap <linux-omap@...r.kernel.org>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	Felipe Balbi <balbi@...com>, Nishanth Menon <nm@...com>
Subject: Re: [PATCH v2] futex: lower the lock contention on the HB lock during
 wake up

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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