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Subject[PATCH 3/3] cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT
Date
With this lock around __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT), we
get circular dependency when we call sysfs_remove_group().

[ 195.319079] ======================================================
[ 195.337653] [ INFO: possible circular locking dependency detected ]
[ 195.356497] 3.9.0-rc7+ #15 Not tainted
[ 195.367758] -------------------------------------------------------
[ 195.386613] cat/2387 is trying to acquire lock:
[ 195.400176] (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at: [<c02f6179>] lock_policy_rwsem_read+0x25/0x34
[ 195.428920]
[ 195.428920] but task is already holding lock:
[ 195.446393] (s_active#41){++++.+}, at: [<c00f9bf7>] sysfs_read_file+0x4f/0xcc
[ 195.468305]
[ 195.468305] which lock already depends on the new lock.
[ 195.468305]
[ 195.492830]
[ 195.492830] the existing dependency chain (in reverse order) is:
[ 195.515250]
-> #1 (s_active#41){++++.+}:
[ 195.527647] [<c0055a79>] lock_acquire+0x61/0xbc
[ 195.543129] [<c00fabf1>] sysfs_addrm_finish+0xc1/0x128
[ 195.560362] [<c00f9819>] sysfs_hash_and_remove+0x35/0x64
[ 195.578119] [<c00fbe6f>] remove_files.isra.0+0x1b/0x24
[ 195.595497] [<c00fbea5>] sysfs_remove_group+0x2d/0xa8
[ 195.612469] [<c02f9a0b>] cpufreq_governor_interactive+0x13b/0x35c
[ 195.632668] [<c02f61df>] __cpufreq_governor+0x2b/0x8c
[ 195.649644] [<c02f6579>] __cpufreq_set_policy+0xa9/0xf8
[ 195.667132] [<c02f6b75>] store_scaling_governor+0x61/0x100
[ 195.685404] [<c02f6f4d>] store+0x39/0x60
[ 195.698989] [<c00f9b81>] sysfs_write_file+0xed/0x114
[ 195.715694] [<c00b3fd1>] vfs_write+0x65/0xd8
[ 195.730320] [<c00b424b>] sys_write+0x2f/0x50
[ 195.744943] [<c000cdc1>] ret_fast_syscall+0x1/0x52
[ 195.761135]
-> #0 (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}:
[ 195.778665] [<c0055253>] __lock_acquire+0xef3/0x13dc
[ 195.795371] [<c0055a79>] lock_acquire+0x61/0xbc
[ 195.810776] [<c03ee1f5>] down_read+0x25/0x30
[ 195.825398] [<c02f6179>] lock_policy_rwsem_read+0x25/0x34
[ 195.843410] [<c02f6edd>] show+0x21/0x58
[ 195.856731] [<c00f9c0f>] sysfs_read_file+0x67/0xcc
[ 195.872919] [<c00b40a7>] vfs_read+0x63/0xd8
[ 195.887282] [<c00b41fb>] sys_read+0x2f/0x50
[ 195.901645] [<c000cdc1>] ret_fast_syscall+0x1/0x52
[ 195.917863]
[ 195.917863] other info that might help us debug this:
[ 195.917863]
[ 195.941853] Possible unsafe locking scenario:
[ 195.941853]
[ 195.959586] CPU0 CPU1
[ 195.973149] ---- ----
[ 195.986712] lock(s_active#41);
[ 195.996407] lock(&per_cpu(cpu_policy_rwsem, cpu));
[ 196.018912] lock(s_active#41);
[ 196.036161] lock(&per_cpu(cpu_policy_rwsem, cpu));
[ 196.051051]
[ 196.051051] *** DEADLOCK ***
[ 196.051051]
[ 196.068792] 2 locks held by cat/2387:
[ 196.079750] #0: (&buffer->mutex){+.+.+.}, at: [<c00f9bcd>] sysfs_read_file+0x25/0xcc
[ 196.103546] #1: (s_active#41){++++.+}, at: [<c00f9bf7>] sysfs_read_file+0x4f/0xcc
[ 196.126577]
[ 196.126577] stack backtrace:
[ 196.139644] [<c0011d55>] (unwind_backtrace+0x1/0x9c) from [<c03e9a09>] (print_circular_bug+0x19d/0x1e8)
[ 196.167857] [<c03e9a09>] (print_circular_bug+0x19d/0x1e8) from [<c0055253>] (__lock_acquire+0xef3/0x13dc)
[ 196.196542] [<c0055253>] (__lock_acquire+0xef3/0x13dc) from [<c0055a79>] (lock_acquire+0x61/0xbc)
[ 196.223139] [<c0055a79>] (lock_acquire+0x61/0xbc) from [<c03ee1f5>] (down_read+0x25/0x30)
[ 196.247722] [<c03ee1f5>] (down_read+0x25/0x30) from [<c02f6179>] (lock_policy_rwsem_read+0x25/0x34)
[ 196.274905] [<c02f6179>] (lock_policy_rwsem_read+0x25/0x34) from [<c02f6edd>] (show+0x21/0x58)
[ 196.300724] [<c02f6edd>] (show+0x21/0x58) from [<c00f9c0f>] (sysfs_read_file+0x67/0xcc)
[ 196.324719] [<c00f9c0f>] (sysfs_read_file+0x67/0xcc) from [<c00b40a7>] (vfs_read+0x63/0xd8)
[ 196.349756] [<c00b40a7>] (vfs_read+0x63/0xd8) from [<c00b41fb>] (sys_read+0x2f/0x50)
[ 196.372970] [<c00b41fb>] (sys_read+0x2f/0x50) from [<c000cdc1>] (ret_fast_syscall+0x1/0x52)

This lock isn't required while calling __cpufreq_governor(policy,
CPUFREQ_GOV_POLICY_EXIT). Remove it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
drivers/cpufreq/cpufreq.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index cb0f723..2d5a829 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1739,18 +1739,23 @@ static int __cpufreq_set_policy(struct cpufreq_policy *data,
/* end old governor */
if (data->governor) {
__cpufreq_governor(data, CPUFREQ_GOV_STOP);
+ unlock_policy_rwsem_write(policy->cpu);
__cpufreq_governor(data,
CPUFREQ_GOV_POLICY_EXIT);
+ lock_policy_rwsem_write(policy->cpu);
}

/* start new governor */
data->governor = policy->governor;
if (!__cpufreq_governor(data, CPUFREQ_GOV_POLICY_INIT)) {
- if (!__cpufreq_governor(data, CPUFREQ_GOV_START))
+ if (!__cpufreq_governor(data, CPUFREQ_GOV_START)) {
failed = 0;
- else
+ } else {
+ unlock_policy_rwsem_write(policy->cpu);
__cpufreq_governor(data,
CPUFREQ_GOV_POLICY_EXIT);
+ lock_policy_rwsem_write(policy->cpu);
+ }
}

if (failed) {
--
1.7.12.rc2.18.g61b472e


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