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Matt Wagantall
48d5672435
store_powersave_bias() acquires the hotplug lock and the dbs_mutex
lock, but does so in the wrong order. Deadlocks like the following
can result.
Thread A:
get_online_cpus+0x3c/0x5c <- acquires 'cpu_hotplug.lock'
store_powersave_bias+0x80/0x3f4 <- acquires 'dbs_mutex'
kobj_attr_store+0x14/0x20
sysfs_write_file+0x108/0x13c
vfs_write+0xb0/0x128
sys_write+0x38/0x64
Thread B:
cpufreq_governor_dbs+0x7c/0x55c <- acquires 'dbs_mutex'
__cpufreq_governor+0x90/0xe0
__cpufreq_set_policy+0x1b0/0x258
cpufreq_add_dev_interface+0x2cc/0x334
cpufreq_add_dev+0x514/0x580
cpufreq_cpu_callback+0x88/0x9c
notifier_call_chain+0x38/0x68
__cpu_notify+0x28/0x40
_cpu_up+0xe4/0x118 <- acquires 'cpu_hotplug.lock'
cpu_up+0x64/0x80
store_online+0x48/0x78
dev_attr_store+0x18/0x24
sysfs_write_file+0x108/0x13c
vfs_write+0xb0/0x128
sys_write+0x38/0x64
Fix this by flipping the order in which the locks are acquired and
released in store_powersave_bias so that it is the same as in the
hotplug path.
Change-Id: Idc59fb29d60b8f7fceb8ed0f2bb9eff4670abda7
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>