On Tuesday, February 09, 2016 09:01:36 AM Viresh Kumar wrote:
An instance of 'struct dbs_data' can support multiple 'struct policy_dbs_info' instances. To traverse all policy_dbs supported by a dbs_data, create a list of policy_dbs within dbs_data.
We can traverse this list now, instead of traversing the loop for all online CPUs in update_sampling_rate(), to solve the circular dependency lockdep reported by Juri (and verified by Shilpa) earlier:
====================================================== [ INFO: possible circular locking dependency detected ] 4.4.0+ #445 Not tainted
trace.sh/1723 is trying to acquire lock: (s_active#48){++++.+}, at: [<c01f78c8>] kernfs_remove_by_name_ns+0x4c/0x94
but task is already holding lock: (od_dbs_cdata.mutex){+.+.+.}, at: [<c05824a0>] cpufreq_governor_dbs+0x34/0x5d4
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (od_dbs_cdata.mutex){+.+.+.}: [<c075b040>] mutex_lock_nested+0x7c/0x434 [<c05824a0>] cpufreq_governor_dbs+0x34/0x5d4 [<c0017c10>] return_to_handler+0x0/0x18
-> #1 (&policy->rwsem){+++++.}: [<c075ca8c>] down_read+0x58/0x94 [<c057c244>] show+0x30/0x60 [<c01f934c>] sysfs_kf_seq_show+0x90/0xfc [<c01f7ad8>] kernfs_seq_show+0x34/0x38 [<c01a22ec>] seq_read+0x1e4/0x4e4 [<c01f8694>] kernfs_fop_read+0x120/0x1a0 [<c01794b4>] __vfs_read+0x3c/0xe0 [<c017a378>] vfs_read+0x98/0x104 [<c017a434>] SyS_read+0x50/0x90 [<c000fd40>] ret_fast_syscall+0x0/0x1c
-> #0 (s_active#48){++++.+}: [<c008238c>] lock_acquire+0xd4/0x20c [<c01f6ae4>] __kernfs_remove+0x288/0x328 [<c01f78c8>] kernfs_remove_by_name_ns+0x4c/0x94 [<c01fa024>] remove_files+0x44/0x88 [<c01fa5a4>] sysfs_remove_group+0x50/0xa4 [<c058285c>] cpufreq_governor_dbs+0x3f0/0x5d4 [<c0017c10>] return_to_handler+0x0/0x18
other info that might help us debug this:
Chain exists of: s_active#48 --> &policy->rwsem --> od_dbs_cdata.mutex
Possible unsafe locking scenario:
CPU0 CPU1 ---- ----lock(od_dbs_cdata.mutex); lock(&policy->rwsem); lock(od_dbs_cdata.mutex); lock(s_active#48);
*** DEADLOCK ***
5 locks held by trace.sh/1723: #0: (sb_writers#6){.+.+.+}, at: [<c017beb8>] __sb_start_write+0xb4/0xc0 #1: (&of->mutex){+.+.+.}, at: [<c01f8418>] kernfs_fop_write+0x6c/0x1c8 #2: (s_active#35){.+.+.+}, at: [<c01f8420>] kernfs_fop_write+0x74/0x1c8 #3: (cpu_hotplug.lock){++++++}, at: [<c0029e6c>] get_online_cpus+0x48/0xb8 #4: (od_dbs_cdata.mutex){+.+.+.}, at: [<c05824a0>] cpufreq_governor_dbs+0x34/0x5d4
stack backtrace: CPU: 2 PID: 1723 Comm: trace.sh Not tainted 4.4.0+ #445 Hardware name: ARM-Versatile Express [<c001883c>] (unwind_backtrace) from [<c0013f50>] (show_stack+0x20/0x24) [<c0013f50>] (show_stack) from [<c044ad90>] (dump_stack+0x80/0xb4) [<c044ad90>] (dump_stack) from [<c0128edc>] (print_circular_bug+0x29c/0x2f0) [<c0128edc>] (print_circular_bug) from [<c0081708>] (__lock_acquire+0x163c/0x1d74) [<c0081708>] (__lock_acquire) from [<c008238c>] (lock_acquire+0xd4/0x20c) [<c008238c>] (lock_acquire) from [<c01f6ae4>] (__kernfs_remove+0x288/0x328) [<c01f6ae4>] (__kernfs_remove) from [<c01f78c8>] (kernfs_remove_by_name_ns+0x4c/0x94) [<c01f78c8>] (kernfs_remove_by_name_ns) from [<c01fa024>] (remove_files+0x44/0x88) [<c01fa024>] (remove_files) from [<c01fa5a4>] (sysfs_remove_group+0x50/0xa4) [<c01fa5a4>] (sysfs_remove_group) from [<c058285c>] (cpufreq_governor_dbs+0x3f0/0x5d4) [<c058285c>] (cpufreq_governor_dbs) from [<c0017c10>] (return_to_handler+0x0/0x18)
This also updates the comment above update_sampling_rate() to make it more relevant to the current state of code.
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
drivers/cpufreq/cpufreq_governor.c | 22 ++++++++-- drivers/cpufreq/cpufreq_governor.h | 7 ++- drivers/cpufreq/cpufreq_ondemand.c | 89 +++++++++++++------------------------- 3 files changed, 54 insertions(+), 64 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index bba9d3fb8103..8e53f804a5af 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -384,9 +384,14 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy) ret = -EINVAL; goto free_policy_dbs_info; }
dbs_data->usage_count++;
mutex_lock(&dbs_data->mutex);dbs_data->usage_count++;list_add(&policy_dbs->list, &dbs_data->policy_dbs_list);mutex_unlock(&dbs_data->mutex);- return 0; }
@@ -396,7 +401,7 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy) goto free_policy_dbs_info; }
- dbs_data->usage_count = 1;
- INIT_LIST_HEAD(&dbs_data->policy_dbs_list); mutex_init(&dbs_data->mutex);
ret = gov->init(dbs_data, !policy->governor->initialized); @@ -417,9 +422,12 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy) if (!have_governor_per_policy()) gov->gdbs_data = dbs_data;
- policy_dbs->dbs_data = dbs_data; policy->governor_data = policy_dbs;
- policy_dbs->dbs_data = dbs_data;
- dbs_data->usage_count = 1;
- list_add(&policy_dbs->list, &dbs_data->policy_dbs_list);
- gov->kobj_type.sysfs_ops = &governor_sysfs_ops; ret = kobject_init_and_add(&dbs_data->kobj, &gov->kobj_type, get_governor_parent_kobj(policy),
@@ -450,12 +458,18 @@ static int cpufreq_governor_exit(struct cpufreq_policy *policy) struct dbs_governor *gov = dbs_governor_of(policy); struct policy_dbs_info *policy_dbs = policy->governor_data; struct dbs_data *dbs_data = policy_dbs->dbs_data;
- int count;
/* State should be equivalent to INIT */ if (policy_dbs->policy) return -EBUSY;
- if (!--dbs_data->usage_count) {
- mutex_lock(&dbs_data->mutex);
- list_del(&policy_dbs->list);
- count = dbs_data->usage_count--;
This appears to be planting a bug.
The way you wrote it the decrementation will take place after the assignment, so count will contain the old value.
- mutex_unlock(&dbs_data->mutex);
- if (!count) { kobject_put(&dbs_data->kobj);
policy->governor_data = NULL;
Thanks, Rafael