forked from Minki/linux
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: 955ef48335
(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>
This commit is contained in:
parent
fd8ddc482a
commit
68e80dae09
@ -2205,10 +2205,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
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return ret;
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}
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up_write(&policy->rwsem);
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ret = __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
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down_write(&policy->rwsem);
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if (ret) {
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pr_err("%s: Failed to Exit Governor: %s (%d)\n",
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__func__, old_gov->name, ret);
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@ -2224,9 +2221,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
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if (!ret)
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goto out;
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up_write(&policy->rwsem);
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__cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
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down_write(&policy->rwsem);
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}
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/* new governor failed, so re-start old one */
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@ -100,10 +100,6 @@ struct cpufreq_policy {
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* - Any routine that will write to the policy structure and/or may take away
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* the policy altogether (eg. CPU hotplug), will hold this lock in write
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* mode before doing so.
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*
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* Additional rules:
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* - Lock should not be held across
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* __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT);
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*/
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struct rw_semaphore rwsem;
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