From: Waiman Long <longman@redhat.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Viresh Kumar <viresh.kumar@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Waiman Long <longman@redhat.com>
Subject: [PATCH 0/2] cpufreq: Fix a circular lock dependency problem
Date: Mon, 23 Jul 2018 13:49:37 -0400 [thread overview]
Message-ID: <1532368179-15263-1-git-send-email-longman@redhat.com> (raw)
This patchset works around a circular lock dependency issue in the
cpufreq driver reported by lockdep. The two locks involved are the
cpu_hotplup_lock and the reference count of a sysfs file.
The cpufreq_register_driver() function uses the lock sequence:
cpus_read_lock --> kn->count
Whereas the cpufreq sysfs store method uses the sequence:
kn->count --> cpus_read_lock
This is not really an issue as a shared lock is used on the
cpu_hotplup_lock. However, the lockdep code isn't able to handle
shared locking. So one way to work around this is to define a
cpus_read_trylock() function and uses it in the store method instead.
Waiman Long (2):
cpu/hotplug: Add a cpus_read_trylock() function
cpufreq: Fix a circular lock dependency problem
drivers/cpufreq/cpufreq.c | 16 +++++++++++++++-
include/linux/cpu.h | 2 ++
kernel/cpu.c | 6 ++++++
3 files changed, 23 insertions(+), 1 deletion(-)
--
1.8.3.1
next reply other threads:[~2018-07-23 17:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-23 17:49 Waiman Long [this message]
2018-07-23 17:49 ` [PATCH 1/2] cpu/hotplug: Add a cpus_read_trylock() function Waiman Long
2018-07-23 17:49 ` [PATCH 2/2] cpufreq: Fix a circular lock dependency problem Waiman Long
2018-07-23 19:16 ` Peter Zijlstra
2018-07-23 19:27 ` Waiman Long
2018-07-24 8:36 ` Rafael J. Wysocki
2018-07-24 8:31 ` Rafael J. Wysocki
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