I have not been able to reliably reproduce the hardware failure that caused
the warning. In order to reproduce this I resorted to (sorry for the
cut-and-paste)
diff --git a/drivers/cpufreq/pcc-cpufreq.c
b/drivers/cpufreq/pcc-cpufreq.c
index 728a2d8..c7724d2 100644
--- a/drivers/cpufreq/pcc-cpufreq.c
+++ b/drivers/cpufreq/pcc-cpufreq.c
@@ -146,6 +146,8 @@ static unsigned int pcc_get_freq(unsigned int cpu)
u32 input_buffer;
u32 output_buffer;
+ return 0;
+
spin_lock(&pcc_lock);
pr_debug("get: get_freq for CPU %d\n", cpu);
to simulate the cpufreq_driver->get() hardware failure.
---8<---
While debugging a cpufreq-related hardware failure on a system I saw the
following lockdep warning:
=========================
[ BUG: held lock freed! ] 3.17.0-rc4+ #1 Tainted: G E
-------------------------
insmod/2247 is freeing memory ffff88006e1b1400-ffff88006e1b17ff, with a lock
still held there!
(&policy->rwsem){+.+...}, at: [<ffffffff8156d37d>]
__cpufreq_add_dev.isra.21+0x47d/0xb80
3 locks held by insmod/2247:
#0: (subsys mutex#5){+.+.+.}, at: [<ffffffff81485579>]
subsys_interface_register+0x69/0x120
#1: (cpufreq_rwsem){.+.+.+}, at: [<ffffffff8156cf73>]
__cpufreq_add_dev.isra.21+0x73/0xb80
#2: (&policy->rwsem){+.+...}, at: [<ffffffff8156d37d>]
__cpufreq_add_dev.isra.21+0x47d/0xb80
stack backtrace:
CPU: 0 PID: 2247 Comm: insmod Tainted: G E 3.17.0-rc4+ #1
Hardware name: HP ProLiant MicroServer Gen8, BIOS J06 08/24/2013
0000000000000000 000000008f3063c4 ffff88006f87bb30 ffffffff8171b358
ffff88006bcf3750 ffff88006f87bb68 ffffffff810e09e1 ffff88006e1b1400
ffffea0001b86c00 ffffffff8156d327 ffff880073003500 0000000000000246
Call Trace:
[<ffffffff8171b358>] dump_stack+0x4d/0x66
[<ffffffff810e09e1>] debug_check_no_locks_freed+0x171/0x180
[<ffffffff8156d327>] ? __cpufreq_add_dev.isra.21+0x427/0xb80
[<ffffffff8121412b>] kfree+0xab/0x2b0
[<ffffffff8156d327>] __cpufreq_add_dev.isra.21+0x427/0xb80
[<ffffffff81724cf7>] ? _raw_spin_unlock+0x27/0x40
[<ffffffffa003517f>] ? pcc_cpufreq_do_osc+0x17f/0x17f [pcc_cpufreq]
[<ffffffff8156da8e>] cpufreq_add_dev+0xe/0x10
[<ffffffff814855d1>] subsys_interface_register+0xc1/0x120
[<ffffffff8156bcf2>] cpufreq_register_driver+0x112/0x340
[<ffffffff8121415a>] ? kfree+0xda/0x2b0
[<ffffffffa003517f>] ? pcc_cpufreq_do_osc+0x17f/0x17f [pcc_cpufreq]
[<ffffffffa003562e>] pcc_cpufreq_init+0x4af/0xe81 [pcc_cpufreq]
[<ffffffffa003517f>] ? pcc_cpufreq_do_osc+0x17f/0x17f [pcc_cpufreq]
[<ffffffff81002144>] do_one_initcall+0xd4/0x210
[<ffffffff811f7472>] ? __vunmap+0xd2/0x120
[<ffffffff81127155>] load_module+0x1315/0x1b70
[<ffffffff811222a0>] ? store_uevent+0x70/0x70
[<ffffffff811229d9>] ? copy_module_from_fd.isra.44+0x129/0x180
[<ffffffff81127b86>] SyS_finit_module+0xa6/0xd0
[<ffffffff81725b69>] system_call_fastpath+0x16/0x1b
cpufreq: __cpufreq_add_dev: ->get() failed
insmod: ERROR: could not insert module pcc-cpufreq.ko: No such device
The warning occurs in the __cpufreq_add_dev() code which does
down_write(&policy->rwsem);
...
if (cpufreq_driver->get && !cpufreq_driver->setpolicy) {
policy->cur = cpufreq_driver->get(policy->cpu);
if (!policy->cur) {
pr_err("%s: ->get() failed\n", __func__);
goto err_get_freq;
}
If cpufreq_driver->get(policy->cpu) returns an error we execute the
code at err_get_freq, which does not up the policy->rwsem. This causes
the lockdep warning.
Trivial patch to up the policy->rwsem in the error path.
After the patch has been applied, and an error occurs in the
cpufreq_driver->get(policy->cpu) call we will now see
cpufreq: __cpufreq_add_dev: ->get() failed
cpufreq: __cpufreq_add_dev: ->get() failed
modprobe: ERROR: could not insert 'pcc_cpufreq': No such device
Signed-off-by: Prarit Bhargava <pra...@redhat.com>
Cc: "Rafael J. Wysocki" <r...@rjwysocki.net>
Cc: Viresh Kumar <viresh.ku...@linaro.org>
Cc: linux...@vger.kernel.org
---
drivers/cpufreq/cpufreq.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index d9fdedd..aadaed0 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1289,6 +1289,8 @@ err_get_freq:
per_cpu(cpufreq_cpu_data, j) = NULL;
write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ up_write(&policy->rwsem);
+
if (cpufreq_driver->exit)
cpufreq_driver->exit(policy);
err_set_policy_cpu:
--
1.7.9.3
--
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