Commits
Viresh Kumar committed 955ef483357
cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT
With the rwsem lock around
__cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT), we
get circular dependency when we call sysfs_remove_group().
======================================================
[ INFO: possible circular locking dependency detected ]
3.9.0-rc7+ #15 Not tainted
-------------------------------------------------------
cat/2387 is trying to acquire lock:
(&per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at: [<c02f6179>] lock_policy_rwsem_read+0x25/0x34
but task is already holding lock:
(s_active#41){++++.+}, at: [<c00f9bf7>] sysfs_read_file+0x4f/0xcc
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (s_active#41){++++.+}:
[<c0055a79>] lock_acquire+0x61/0xbc
[<c00fabf1>] sysfs_addrm_finish+0xc1/0x128
[<c00f9819>] sysfs_hash_and_remove+0x35/0x64
[<c00fbe6f>] remove_files.isra.0+0x1b/0x24
[<c00fbea5>] sysfs_remove_group+0x2d/0xa8
[<c02f9a0b>] cpufreq_governor_interactive+0x13b/0x35c
[<c02f61df>] __cpufreq_governor+0x2b/0x8c
[<c02f6579>] __cpufreq_set_policy+0xa9/0xf8
[<c02f6b75>] store_scaling_governor+0x61/0x100
[<c02f6f4d>] store+0x39/0x60
[<c00f9b81>] sysfs_write_file+0xed/0x114
[<c00b3fd1>] vfs_write+0x65/0xd8
[<c00b424b>] sys_write+0x2f/0x50
[<c000cdc1>] ret_fast_syscall+0x1/0x52
-> #0 (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}:
[<c0055253>] __lock_acquire+0xef3/0x13dc
[<c0055a79>] lock_acquire+0x61/0xbc
[<c03ee1f5>] down_read+0x25/0x30
[<c02f6179>] lock_policy_rwsem_read+0x25/0x34
[<c02f6edd>] show+0x21/0x58
[<c00f9c0f>] sysfs_read_file+0x67/0xcc
[<c00b40a7>] vfs_read+0x63/0xd8
[<c00b41fb>] sys_read+0x2f/0x50
[<c000cdc1>] ret_fast_syscall+0x1/0x52
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(s_active#41);
lock(&per_cpu(cpu_policy_rwsem, cpu));
lock(s_active#41);
lock(&per_cpu(cpu_policy_rwsem, cpu));
*** DEADLOCK ***
2 locks held by cat/2387:
#0: (&buffer->mutex){+.+.+.}, at: [<c00f9bcd>] sysfs_read_file+0x25/0xcc
#1: (s_active#41){++++.+}, at: [<c00f9bf7>] sysfs_read_file+0x4f/0xcc
stack backtrace:
[<c0011d55>] (unwind_backtrace+0x1/0x9c) from [<c03e9a09>] (print_circular_bug+0x19d/0x1e8)
[<c03e9a09>] (print_circular_bug+0x19d/0x1e8) from [<c0055253>] (__lock_acquire+0xef3/0x13dc)
[<c0055253>] (__lock_acquire+0xef3/0x13dc) from [<c0055a79>] (lock_acquire+0x61/0xbc)
[<c0055a79>] (lock_acquire+0x61/0xbc) from [<c03ee1f5>] (down_read+0x25/0x30)
[<c03ee1f5>] (down_read+0x25/0x30) from [<c02f6179>] (lock_policy_rwsem_read+0x25/0x34)
[<c02f6179>] (lock_policy_rwsem_read+0x25/0x34) from [<c02f6edd>] (show+0x21/0x58)
[<c02f6edd>] (show+0x21/0x58) from [<c00f9c0f>] (sysfs_read_file+0x67/0xcc)
[<c00f9c0f>] (sysfs_read_file+0x67/0xcc) from [<c00b40a7>] (vfs_read+0x63/0xd8)
[<c00b40a7>] (vfs_read+0x63/0xd8) from [<c00b41fb>] (sys_read+0x2f/0x50)
[<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>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>