diff options
author | Viresh Kumar <viresh.kumar@linaro.org> | 2016-02-09 06:31:35 +0300 |
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committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2016-03-09 16:40:59 +0300 |
commit | 68e80dae09033d778b98dc88e5bfe8fdade188e5 (patch) | |
tree | 0571ae04e4cf5be1135caae77d877aec08f08236 /include/linux/cpufreq.h | |
parent | fd8ddc482a7a5e015c0613c4d96543d5efad047c (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 'include/linux/cpufreq.h')
-rw-r--r-- | include/linux/cpufreq.h | 4 |
1 files changed, 0 insertions, 4 deletions
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 704d85bf7242..cac3d1ba8200 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -100,10 +100,6 @@ struct cpufreq_policy { * - 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 * mode before doing so. - * - * Additional rules: - * - Lock should not be held across - * __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT); */ struct rw_semaphore rwsem; |