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Message-Id: <e03b6a7bccda26e5b94dd00c3068fdc4e22c14eb.1454988295.git.viresh.kumar@linaro.org>
Date: Tue, 9 Feb 2016 09:01:35 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Rafael Wysocki <rjw@...ysocki.net>, juri.lelli@....com
Cc: linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
skannan@...eaurora.org, peterz@...radead.org,
mturquette@...libre.com, steve.muckle@...aro.org,
vincent.guittot@...aro.org, morten.rasmussen@....com,
dietmar.eggemann@....com, shilpa.bhat@...ux.vnet.ibm.com,
linux-kernel@...r.kernel.org,
Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH V4 5/6] Revert "cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT"
Earlier, when the struct freq-attr was used to represent governor
attributes, the standard cpufreq show/store sysfs attribute callbacks
were applied to the governor tunable attributes and they always acquire
the policy->rwsem lock before carrying out the operation. That could
have resulted in an ABBA deadlock if governor tunable attributes are
removed under policy->rwsem while one of them is being accessed
concurrently (if sysfs attributes removal wins the race, it will wait
for the access to complete with policy->rwsem held while the attribute
callback will block on policy->rwsem indefinitely).
We attempted to address this issue by dropping policy->rwsem around
governor tunable attributes removal (that is, around invocations of the
->governor callback with the event arg equal to CPUFREQ_GOV_POLICY_EXIT)
in cpufreq_set_policy(), but that opened up race conditions that had not
been possible with policy->rwsem held all the time.
The previous commit, "cpufreq: governor: New sysfs show/store callbacks
for governor tunables", fixed the original ABBA deadlock by adding new
governor specific show/store callbacks.
We don't have to drop rwsem around invocations of governor event
CPUFREQ_GOV_POLICY_EXIT anymore, and original fix can be reverted now.
Fixes: 955ef4833574 ("cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT")
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
Reported-by: Juri Lelli <juri.lelli@....com>
Tested-by: Juri Lelli <juri.lelli@....com>
Tested-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
---
drivers/cpufreq/cpufreq.c | 5 -----
include/linux/cpufreq.h | 4 ----
2 files changed, 9 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 29755fcbf200..9c62bf35b9dc 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2204,10 +2204,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
return ret;
}
- up_write(&policy->rwsem);
ret = __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
- down_write(&policy->rwsem);
-
if (ret) {
pr_err("%s: Failed to Exit Governor: %s (%d)\n",
__func__, old_gov->name, ret);
@@ -2223,9 +2220,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
if (!ret)
goto out;
- up_write(&policy->rwsem);
__cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
- down_write(&policy->rwsem);
}
/* new governor failed, so re-start old one */
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 11aa93134493..2a029c587975 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -100,10 +100,6 @@ struct cpufreq_policy {
* - Any routine that will write to the policy structure and/or may take away
* the policy altogether (eg. CPU hotplug), will hold this lock in write
* mode before doing so.
- *
- * Additional rules:
- * - Lock should not be held across
- * __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT);
*/
struct rw_semaphore rwsem;
--
2.7.1.370.gb2aa7f8
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