• Viresh Kumar's avatar
    Revert "cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT" · 68e80dae
    Viresh Kumar authored
    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>
    68e80dae