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authorViresh Kumar <viresh.kumar@linaro.org>2016-02-09 09:01:35 +0530
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-03-09 14:40:59 +0100
commit68e80dae09033d778b98dc88e5bfe8fdade188e5 (patch)
tree0571ae04e4cf5be1135caae77d877aec08f08236 /drivers/cpufreq
parentfd8ddc482a7a5e015c0613c4d96543d5efad047c (diff)
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@linaro.org> Reported-by: Juri Lelli <juri.lelli@arm.com> Tested-by: Juri Lelli <juri.lelli@arm.com> Tested-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/cpufreq')
-rw-r--r--drivers/cpufreq/cpufreq.c5
1 files changed, 0 insertions, 5 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index e172b2a02c1d..e92e9eab7c6c 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2205,10 +2205,7 @@ 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);
@@ -2224,9 +2221,7 @@ 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 */