BugLink: https://bugs.launchpad.net/bugs/1878232

commit 68e80dae upstream.

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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>