Commit 68e80dae authored by Viresh Kumar's avatar Viresh Kumar Committed by Rafael J. Wysocki

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: 955ef483 (cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT)
Signed-off-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Reported-by: default avatarJuri Lelli <juri.lelli@arm.com>
Tested-by: default avatarJuri Lelli <juri.lelli@arm.com>
Tested-by: default avatarShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent fd8ddc48
...@@ -2205,10 +2205,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, ...@@ -2205,10 +2205,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
return ret; return ret;
} }
up_write(&policy->rwsem);
ret = __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT); ret = __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
down_write(&policy->rwsem);
if (ret) { if (ret) {
pr_err("%s: Failed to Exit Governor: %s (%d)\n", pr_err("%s: Failed to Exit Governor: %s (%d)\n",
__func__, old_gov->name, ret); __func__, old_gov->name, ret);
...@@ -2224,9 +2221,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, ...@@ -2224,9 +2221,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
if (!ret) if (!ret)
goto out; goto out;
up_write(&policy->rwsem);
__cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT); __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
down_write(&policy->rwsem);
} }
/* new governor failed, so re-start old one */ /* new governor failed, so re-start old one */
......
...@@ -100,10 +100,6 @@ struct cpufreq_policy { ...@@ -100,10 +100,6 @@ struct cpufreq_policy {
* - Any routine that will write to the policy structure and/or may take away * - 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 * the policy altogether (eg. CPU hotplug), will hold this lock in write
* mode before doing so. * mode before doing so.
*
* Additional rules:
* - Lock should not be held across
* __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT);
*/ */
struct rw_semaphore rwsem; struct rw_semaphore rwsem;
......
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