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From:   Julien Desfossez <jdesfossez@digitalocean.com>
To:     Peter Zijlstra <peterz@infradead.org>, mingo@kernel.org,
        tglx@linutronix.de, pjt@google.com, tim.c.chen@linux.intel.com,
        torvalds@linux-foundation.org
Cc:     Julien Desfossez <jdesfossez@digitalocean.com>,
        linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com,
        fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
        Vineeth Pillai <vpillai@digitalocean.com>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>
Subject: Re: [RFC][PATCH 03/16] sched: Wrap rq::lock access
Date:   Mon, 18 Mar 2019 11:41:50 -0400
Message-Id: <1552923710-30933-1-git-send-email-jdesfossez@digitalocean.com>
In-Reply-To: <20190218173514.064516553@infradead.org>
References: <20190218173514.064516553@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@digitalocean.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