linux-kernel - Re: [RFC][PATCH 03/16] sched: Wrap rq::lock access

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Date:   Mon, 18 Mar 2019 11:41:50 -0400
From:   Julien Desfossez <jdesfossez@...italocean.com>
To:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        tglx@...utronix.de, pjt@...gle.com, tim.c.chen@...ux.intel.com,
        torvalds@...ux-foundation.org
Cc:     Julien Desfossez <jdesfossez@...italocean.com>,
        linux-kernel@...r.kernel.org, subhra.mazumdar@...cle.com,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Vineeth Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>
Subject: Re: [RFC][PATCH 03/16] sched: Wrap rq::lock access

The case where we try to acquire the lock on 2 runqueues belonging to 2
different cores requires the rq_lockp wrapper as well otherwise we
frequently deadlock in there.

This fixes the crash reported in
1552577311-8218-1-git-send-email-jdesfossez@...italocean.com

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 76fee56..71bb71f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2078,7 +2078,7 @@ static inline void double_rq_lock(struct rq *rq1, struct rq *rq2)
 		raw_spin_lock(rq_lockp(rq1));
 		__acquire(rq2->lock);	/* Fake it out ;) */
 	} else {
-		if (rq1 < rq2) {
+		if (rq_lockp(rq1) < rq_lockp(rq2)) {
 			raw_spin_lock(rq_lockp(rq1));
 			raw_spin_lock_nested(rq_lockp(rq2), SINGLE_DEPTH_NESTING);
 		} else {
-- 
2.7.4