On Mon, Feb 8, 2016 at 12:39 PM, Viresh Kumar viresh.kumar@linaro.org wrote:
Now that we maintain a list of all 'struct policy_dbs_info' for an instance of 'struct dbs_data', we can traverse that instead of traversing the loop for all online CPUs.
This also solves 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)
Reported-by: Juri Lelli juri.lelli@arm.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.org
drivers/cpufreq/cpufreq_ondemand.c | 89 ++++++++++---------------------------- 1 file changed, 22 insertions(+), 67 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c index 745290d7f6a2..f72087bc8302 100644 --- a/drivers/cpufreq/cpufreq_ondemand.c +++ b/drivers/cpufreq/cpufreq_ondemand.c @@ -224,83 +224,38 @@ static struct dbs_governor od_dbs_gov; /**
- update_sampling_rate - update sampling rate effective immediately if needed.
- @new_rate: new sampling rate
- If new rate is smaller than the old, simply updating
- dbs_tuners_int.sampling_rate might not be appropriate. For example, if the
- original sampling_rate was 1 second and the requested new sampling rate is 10
- ms because the user needs immediate reaction from ondemand governor, but not
- sure if higher frequency will be required or not, then, the governor may
- change the sampling rate too late; up to 1 second later. Thus, if we are
- reducing the sampling rate, we need to make the new value effective
- immediately.
The comment still applies.
Moreover, please extend it to say that this must be called with dbs_data->mutex held (or it looks racy otherwise).
Thanks, Rafael
On Mon, Feb 8, 2016 at 12:39 PM, Viresh Kumar viresh.kumar@linaro.org wrote:
Now that we maintain a list of all 'struct policy_dbs_info' for an instance of 'struct dbs_data', we can traverse that instead of traversing the loop for all online CPUs.
This also solves 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)
Reported-by: Juri Lelli juri.lelli@arm.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.org
drivers/cpufreq/cpufreq_ondemand.c | 89 ++++++++++---------------------------- 1 file changed, 22 insertions(+), 67 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c index 745290d7f6a2..f72087bc8302 100644 --- a/drivers/cpufreq/cpufreq_ondemand.c +++ b/drivers/cpufreq/cpufreq_ondemand.c @@ -224,83 +224,38 @@ static struct dbs_governor od_dbs_gov; /**
- update_sampling_rate - update sampling rate effective immediately if needed.
- @new_rate: new sampling rate
- If new rate is smaller than the old, simply updating
- dbs_tuners_int.sampling_rate might not be appropriate. For example, if the
- original sampling_rate was 1 second and the requested new sampling rate is 10
- ms because the user needs immediate reaction from ondemand governor, but not
- sure if higher frequency will be required or not, then, the governor may
- change the sampling rate too late; up to 1 second later. Thus, if we are
- reducing the sampling rate, we need to make the new value effective
*/
- immediately.
static void update_sampling_rate(struct dbs_data *dbs_data) {
struct cpumask cpumask;
struct policy_dbs_info *policy_dbs; unsigned int new_rate = dbs_data->sampling_rate;
int cpu; /** Lock governor so that governor start/stop can't execute in parallel.
* We are operating under dbs_data->mutex and so the list and its* entries can't be freed concurrently. */
mutex_lock(&dbs_data_mutex);cpumask_copy(&cpumask, cpu_online_mask);for_each_cpu(cpu, &cpumask) {struct cpufreq_policy *policy;struct od_cpu_dbs_info_s *dbs_info;struct cpu_dbs_info *cdbs;struct policy_dbs_info *policy_dbs;dbs_info = &per_cpu(od_cpu_dbs_info, cpu);cdbs = &dbs_info->cdbs;policy_dbs = cdbs->policy_dbs;
list_for_each_entry(policy_dbs, &dbs_data->policy_dbs_list, list) {mutex_lock(&policy_dbs->timer_mutex); /*
* A valid policy_dbs means governor hasn't stopped or exited* yet.
* On 32-bit architectures this may race with the* sample_delay_ns read in dbs_update_util_handler(), but that* really doesn't matter. If the read returns a value that's* too big, the sample will be skipped, but the next invocation* of dbs_update_util_handler() (when the update has been* completed) will take a sample. If the returned value is too* small, the sample will be taken immediately, but that isn't a* problem, as we want the new rate to take effect immediately* anyway.** If this runs in parallel with dbs_work_handler(), we may end* up overwriting the sample_delay_ns value that it has just* written, but the difference should not be too big and it will* be corrected next time a sample is taken, so it shouldn't be* significant. */
if (!policy_dbs)continue;policy = policy_dbs->policy;/* clear all CPUs of this policy */cpumask_andnot(&cpumask, &cpumask, policy->cpus);/** Update sampling rate for CPUs whose policy is governed by* dbs_data. In case of governor_per_policy, only a single* policy will be governed by dbs_data, otherwise there can be* multiple policies that are governed by the same dbs_data.*/if (dbs_data == policy_dbs->dbs_data) {mutex_lock(&policy_dbs->timer_mutex);/** On 32-bit architectures this may race with the* sample_delay_ns read in dbs_update_util_handler(),* but that really doesn't matter. If the read returns* a value that's too big, the sample will be skipped,* but the next invocation of dbs_update_util_handler()* (when the update has been completed) will take a* sample. If the returned value is too small, the* sample will be taken immediately, but that isn't a* problem, as we want the new rate to take effect* immediately anyway.** If this runs in parallel with dbs_work_handler(), we* may end up overwriting the sample_delay_ns value that* it has just written, but the difference should not be* too big and it will be corrected next time a sample* is taken, so it shouldn't be significant.*/gov_update_sample_delay(policy_dbs, new_rate);mutex_unlock(&policy_dbs->timer_mutex);}
gov_update_sample_delay(policy_dbs, new_rate);mutex_unlock(&policy_dbs->timer_mutex); }
mutex_unlock(&dbs_data_mutex);}
static bool invalid_up_threshold(struct dbs_data *dbs_data,
2.7.1.370.gb2aa7f8
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