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Date: Tue, 03 Sep 2013 18:48:20 +0530
From: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
CC: "Rafael J. Wysocki" <rjw@...k.pl>,
Stephen Boyd <sboyd@...eaurora.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: mutex warning in cpufreq + RFC patch
On 09/01/2013 09:51 PM, Viresh Kumar wrote:
> On 1 September 2013 18:52, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> On Sunday, September 01, 2013 11:54:10 AM Viresh Kumar wrote:
>>> Btw, I am facing another crash which I am not sure how to fix.. It
>>> came with your script:
>>
>> This isn't a crash, but a WARN_ON_ONCE() triggering. The comment in kref_get()
>> explains when that occurs, so we seem to have a race between
>> store_scaling_min_freq() and CPU removal.
>
> Yeah, I meant the same thing.. I don't know how to solve it or what's
> the correct way to solve it:
>
> I tried this:
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 4d5723db..be2e5f4 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -200,8 +200,14 @@ struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
> if (cpufreq_driver) {
> /* get the CPU */
> policy = per_cpu(cpufreq_cpu_data, cpu);
> - if (policy)
> - kobject_get(&policy->kobj);
> + if (policy) {
> + cpu_hotplug_disable();
> + if (unlikely(!cpu_online(policy->cpu)))
> + policy = NULL;
> + else
> + kobject_get(&policy->kobj);
> + cpu_hotplug_enable();
> + }
> }
>
> And this gave another crash:
>
> [ 246.724464] INFO: task irqbalance:1052 blocked for more than 120 seconds.
> [ 246.724474] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 246.724479] irqbalance D 0000000000000000 0 1052 1 0x00000000
> [ 246.724489] ffff88002f2dfd78 0000000000000086 ffff88002e53b800
> 0000000000000001
> [ 246.724498] ffff880030620000 ffff88002f2dffd8 ffff88002f2dffd8
> ffff88002f2dffd8
> [ 246.724505] ffff880030181700 ffff880030620000 ffff8800ccbfd698
> ffffffff81c981c0
> [ 246.724511] Call Trace:
> [ 246.724525] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 246.724532] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 246.724543] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 246.724552] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 246.724561] [<ffffffff81416e15>] lock_device_hotplug+0x15/0x20
> [ 246.724568] [<ffffffff81416e60>] show_online+0x20/0x60
> [ 246.724574] [<ffffffff81415ab0>] dev_attr_show+0x20/0x60
> [ 246.724583] [<ffffffff81129a3e>] ? __get_free_pages+0xe/0x40
> [ 246.724592] [<ffffffff811f2c9a>] sysfs_read_file+0xaa/0x180
> [ 246.724602] [<ffffffff81182074>] vfs_read+0xb4/0x180
> [ 246.724610] [<ffffffff811822f2>] SyS_read+0x52/0xa0
> [ 246.724617] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 246.724631] INFO: task preload:1731 blocked for more than 120 seconds.
> [ 246.724634] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 246.724637] preload D ffffffff8180fb60 0 1731 1 0x00000000
> [ 246.724643] ffff8800cca71d28 0000000000000086 ffff8800cca71cc8
> ffffffff8118bafd
> [ 246.724650] ffff88002e7dc500 ffff8800cca71fd8 ffff8800cca71fd8
> ffff8800cca71fd8
> [ 246.724655] ffff880119359700 ffff88002e7dc500 ffff880119408240
> ffffffff81c31b88
> [ 246.724661] Call Trace:
> [ 246.724669] [<ffffffff8118bafd>] ? terminate_walk+0x3d/0x50
> [ 246.724675] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 246.724681] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 246.724690] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 246.724697] [<ffffffff8118ba72>] ? path_put+0x22/0x30
> [ 246.724705] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 246.724713] [<ffffffff8104d19c>] get_online_cpus+0x2c/0x50
> [ 246.724722] [<ffffffff8114196a>] all_vm_events+0x1a/0x120
> [ 246.724730] [<ffffffff81141b05>] vmstat_start+0x95/0xc0
> [ 246.724738] [<ffffffff811a3739>] seq_read+0x139/0x3e0
> [ 246.724747] [<ffffffff812acbb3>] ? security_file_permission+0xa3/0xc0
> [ 246.724755] [<ffffffff811e4083>] proc_reg_read+0x43/0x70
> [ 246.724763] [<ffffffff81182074>] vfs_read+0xb4/0x180
> [ 246.724770] [<ffffffff811822f2>] SyS_read+0x52/0xa0
> [ 246.724776] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 246.724781] INFO: task ondemand:1867 blocked for more than 120 seconds.
> [ 246.724783] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 246.724786] ondemand D ffffffff8180fb60 0 1867 1 0x00000000
> [ 246.724791] ffff8800d66c3ba8 0000000000000082 ffff8800d66c3be8
> ffffffff811c0ba2
> [ 246.724797] ffff88002f1a0000 ffff8800d66c3fd8 ffff8800d66c3fd8
> ffff8800d66c3fd8
> [ 246.724803] ffffffff81c10440 ffff88002f1a0000 0000000000000000
> ffffffff81c31b40
> [ 246.724809] Call Trace:
> [ 246.724817] [<ffffffff811c0ba2>] ? fsnotify+0x1d2/0x2b0
> [ 246.724822] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 246.724828] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 246.724836] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 246.724844] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 246.724850] [<ffffffff8104d1f5>] cpu_maps_update_begin+0x15/0x20
> [ 246.724856] [<ffffffff8104d53e>] cpu_hotplug_disable+0xe/0x20
> [ 246.724866] [<ffffffff81533aad>] cpufreq_cpu_get+0x7d/0xf0
> [ 246.724874] [<ffffffff81533c41>] cpufreq_get_policy+0x21/0x120
> [ 246.724882] [<ffffffff81533d8b>] store_scaling_governor+0x4b/0x1f0
> [ 246.724890] [<ffffffff8118d37a>] ? link_path_walk+0x23a/0x8d0
> [ 246.724897] [<ffffffff8119fae9>] ? mntput_no_expire+0x49/0x160
> [ 246.724902] [<ffffffff8119fc24>] ? mntput+0x24/0x40
> [ 246.724911] [<ffffffff81533000>] store+0x70/0xb0
> [ 246.724919] [<ffffffff811f2582>] sysfs_write_file+0xe2/0x170
> [ 246.724927] [<ffffffff81181e8e>] vfs_write+0xce/0x200
> [ 246.724934] [<ffffffff81182392>] SyS_write+0x52/0xa0
> [ 246.724940] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 246.724961] INFO: task gnome-keyring-d:2989 blocked for more than
> 120 seconds.
> [ 246.724963] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 246.724966] gnome-keyring-d D 0000000000000000 0 2989 1 0x00000000
> [ 246.724971] ffff8800cb933e38 0000000000000086 00000000000000dc
> 0000000000000004
> [ 246.724977] ffff88002e548000 ffff8800cb933fd8 ffff8800cb933fd8
> ffff8800cb933fd8
> [ 246.724982] ffff8800301fae00 ffff88002e548000 ffff88010fbb6b40
> ffffffff81c31b88
> [ 246.724988] Call Trace:
> [ 246.724994] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 246.724999] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 246.725007] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 246.725016] [<ffffffff81133780>] ? __pagevec_release+0x40/0x40
> [ 246.725024] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 246.725030] [<ffffffff8104d19c>] get_online_cpus+0x2c/0x50
> [ 246.725038] [<ffffffff810693d9>] schedule_on_each_cpu+0x39/0x110
> [ 246.725047] [<ffffffff811337a5>] lru_add_drain_all+0x15/0x20
> [ 246.725055] [<ffffffff81150dd8>] SyS_mlock+0x38/0x130
> [ 246.725061] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 246.725083] INFO: task sh:3952 blocked for more than 120 seconds.
> [ 246.725086] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 246.725089] sh D ffffffff8180ff20 0 3952 3947 0x00000004
> [ 246.725093] ffff8800ccd3bbd8 0000000000000082 0000000000000000
> 0000000000000001
> [ 246.725099] ffff8800cb0c9700 ffff8800ccd3bfd8 ffff8800ccd3bfd8
> ffff8800ccd3bfd8
> [ 246.725105] ffff880118c5c500 ffff8800cb0c9700 ffffffff81142619
> ffffffff81c31b40
> [ 246.725110] Call Trace:
> [ 246.725119] [<ffffffff81142619>] ? zone_statistics+0x99/0xc0
> [ 246.725124] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 246.725129] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 246.725137] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 246.725145] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 246.725151] [<ffffffff8104d1f5>] cpu_maps_update_begin+0x15/0x20
> [ 246.725157] [<ffffffff8104d53e>] cpu_hotplug_disable+0xe/0x20
> [ 246.725165] [<ffffffff81533aad>] cpufreq_cpu_get+0x7d/0xf0
> [ 246.725172] [<ffffffff81533c41>] cpufreq_get_policy+0x21/0x120
> [ 246.725180] [<ffffffff8153400f>] store_scaling_min_freq+0x3f/0xa0
> [ 246.725190] [<ffffffff816785e6>] ? down_write+0x16/0x40
> [ 246.725197] [<ffffffff81533000>] store+0x70/0xb0
> [ 246.725205] [<ffffffff811f2582>] sysfs_write_file+0xe2/0x170
> [ 246.725212] [<ffffffff81181e8e>] vfs_write+0xce/0x200
> [ 246.725219] [<ffffffff81182392>] SyS_write+0x52/0xa0
> [ 246.725225] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 246.725229] INFO: task sh:3953 blocked for more than 120 seconds.
> [ 246.725232] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 246.725234] sh D ffffffff8180fb60 0 3953 3952 0x00000004
> [ 246.725239] ffff8800ccd9dbf8 0000000000000082 ffffffff81116bcf
> ffff880119398000
> [ 246.725245] ffff8800c9f65c00 ffff8800ccd9dfd8 ffff8800ccd9dfd8
> ffff8800ccd9dfd8
> [ 246.725251] ffff880119358000 ffff8800c9f65c00 ffff8800ccd9dcc8
> ffffffff81c31b40
> [ 246.725256] Call Trace:
> [ 246.725266] [<ffffffff81116bcf>] ? update_group_times+0xf/0x40
> [ 246.725272] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 246.725277] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 246.725285] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 246.725293] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 246.725298] [<ffffffff8104d1f5>] cpu_maps_update_begin+0x15/0x20
> [ 246.725304] [<ffffffff8104d53e>] cpu_hotplug_disable+0xe/0x20
> [ 246.725312] [<ffffffff81533aad>] cpufreq_cpu_get+0x7d/0xf0
> [ 246.725320] [<ffffffff8153549d>] cpufreq_stats_free_sysfs+0x1d/0x80
> [ 246.725328] [<ffffffff8153559f>] cpufreq_stat_cpu_callback+0x2f/0x40
> [ 246.725336] [<ffffffff8167f17d>] notifier_call_chain+0x4d/0x70
> [ 246.725346] [<ffffffff8107508e>] __raw_notifier_call_chain+0xe/0x10
> [ 246.725351] [<ffffffff8104d0d0>] __cpu_notify+0x20/0x40
> [ 246.725358] [<ffffffff81667171>] _cpu_down+0x81/0x250
> [ 246.725364] [<ffffffff81667375>] cpu_down+0x35/0x50
> [ 246.725370] [<ffffffff8141b9c1>] cpu_subsys_offline+0x21/0x40
> [ 246.725377] [<ffffffff81416f45>] device_offline+0xa5/0xd0
> [ 246.725384] [<ffffffff8141704e>] store_online+0x3e/0x80
> [ 246.725390] [<ffffffff81414568>] dev_attr_store+0x18/0x30
> [ 246.725397] [<ffffffff811f2582>] sysfs_write_file+0xe2/0x170
> [ 246.725404] [<ffffffff81181e8e>] vfs_write+0xce/0x200
> [ 246.725411] [<ffffffff81182392>] SyS_write+0x52/0xa0
> [ 246.725419] [<ffffffff8167f12e>] ? do_page_fault+0xe/0x10
> [ 246.725425] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 366.756425] INFO: task irqbalance:1052 blocked for more than 120 seconds.
> [ 366.756435] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 366.756440] irqbalance D 0000000000000000 0 1052 1 0x00000000
> [ 366.756450] ffff88002f2dfd78 0000000000000086 ffff88002e53b800
> 0000000000000001
> [ 366.756459] ffff880030620000 ffff88002f2dffd8 ffff88002f2dffd8
> ffff88002f2dffd8
> [ 366.756465] ffff880030181700 ffff880030620000 ffff8800ccbfd698
> ffffffff81c981c0
> [ 366.756472] Call Trace:
> [ 366.756486] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 366.756493] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 366.756504] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 366.756513] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 366.756522] [<ffffffff81416e15>] lock_device_hotplug+0x15/0x20
> [ 366.756528] [<ffffffff81416e60>] show_online+0x20/0x60
> [ 366.756535] [<ffffffff81415ab0>] dev_attr_show+0x20/0x60
> [ 366.756544] [<ffffffff81129a3e>] ? __get_free_pages+0xe/0x40
> [ 366.756553] [<ffffffff811f2c9a>] sysfs_read_file+0xaa/0x180
> [ 366.756564] [<ffffffff81182074>] vfs_read+0xb4/0x180
> [ 366.756571] [<ffffffff811822f2>] SyS_read+0x52/0xa0
> [ 366.756579] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 366.756593] INFO: task preload:1731 blocked for more than 120 seconds.
> [ 366.756596] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 366.756599] preload D ffffffff8180fb60 0 1731 1 0x00000000
> [ 366.756605] ffff8800cca71d28 0000000000000086 ffff8800cca71cc8
> ffffffff8118bafd
> [ 366.756611] ffff88002e7dc500 ffff8800cca71fd8 ffff8800cca71fd8
> ffff8800cca71fd8
> [ 366.756617] ffff880119359700 ffff88002e7dc500 ffff880119408240
> ffffffff81c31b88
> [ 366.756623] Call Trace:
> [ 366.756631] [<ffffffff8118bafd>] ? terminate_walk+0x3d/0x50
> [ 366.756637] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 366.756643] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 366.756652] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 366.756659] [<ffffffff8118ba72>] ? path_put+0x22/0x30
> [ 366.756667] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 366.756674] [<ffffffff8104d19c>] get_online_cpus+0x2c/0x50
> [ 366.756684] [<ffffffff8114196a>] all_vm_events+0x1a/0x120
> [ 366.756692] [<ffffffff81141b05>] vmstat_start+0x95/0xc0
> [ 366.756700] [<ffffffff811a3739>] seq_read+0x139/0x3e0
> [ 366.756709] [<ffffffff812acbb3>] ? security_file_permission+0xa3/0xc0
> [ 366.756717] [<ffffffff811e4083>] proc_reg_read+0x43/0x70
> [ 366.756725] [<ffffffff81182074>] vfs_read+0xb4/0x180
> [ 366.756732] [<ffffffff811822f2>] SyS_read+0x52/0xa0
> [ 366.756738] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 366.756743] INFO: task ondemand:1867 blocked for more than 120 seconds.
> [ 366.756745] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 366.756748] ondemand D ffffffff8180fb60 0 1867 1 0x00000000
> [ 366.756753] ffff8800d66c3ba8 0000000000000082 ffff8800d66c3be8
> ffffffff811c0ba2
> [ 366.756759] ffff88002f1a0000 ffff8800d66c3fd8 ffff8800d66c3fd8
> ffff8800d66c3fd8
> [ 366.756765] ffffffff81c10440 ffff88002f1a0000 0000000000000000
> ffffffff81c31b40
> [ 366.756771] Call Trace:
> [ 366.756779] [<ffffffff811c0ba2>] ? fsnotify+0x1d2/0x2b0
> [ 366.756785] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 366.756790] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 366.756798] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 366.756806] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 366.756813] [<ffffffff8104d1f5>] cpu_maps_update_begin+0x15/0x20
> [ 366.756819] [<ffffffff8104d53e>] cpu_hotplug_disable+0xe/0x20
> [ 366.756828] [<ffffffff81533aad>] cpufreq_cpu_get+0x7d/0xf0
> [ 366.756836] [<ffffffff81533c41>] cpufreq_get_policy+0x21/0x120
> [ 366.756845] [<ffffffff81533d8b>] store_scaling_governor+0x4b/0x1f0
> [ 366.756852] [<ffffffff8118d37a>] ? link_path_walk+0x23a/0x8d0
> [ 366.756859] [<ffffffff8119fae9>] ? mntput_no_expire+0x49/0x160
> [ 366.756865] [<ffffffff8119fc24>] ? mntput+0x24/0x40
> [ 366.756874] [<ffffffff81533000>] store+0x70/0xb0
> [ 366.756882] [<ffffffff811f2582>] sysfs_write_file+0xe2/0x170
> [ 366.756889] [<ffffffff81181e8e>] vfs_write+0xce/0x200
> [ 366.756896] [<ffffffff81182392>] SyS_write+0x52/0xa0
> [ 366.756903] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
> [ 366.756922] INFO: task gnome-keyring-d:2989 blocked for more than
> 120 seconds.
> [ 366.756925] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 366.756927] gnome-keyring-d D 0000000000000000 0 2989 1 0x00000000
> [ 366.756932] ffff8800cb933e38 0000000000000086 00000000000000dc
> 0000000000000004
> [ 366.756938] ffff88002e548000 ffff8800cb933fd8 ffff8800cb933fd8
> ffff8800cb933fd8
> [ 366.756944] ffff8800301fae00 ffff88002e548000 ffff88010fbb6b40
> ffffffff81c31b88
> [ 366.756949] Call Trace:
> [ 366.756955] [<ffffffff81679c39>] schedule+0x29/0x70
> [ 366.756961] [<ffffffff81679f1e>] schedule_preempt_disabled+0xe/0x10
> [ 366.756969] [<ffffffff816781d2>] __mutex_lock_slowpath+0x112/0x1b0
> [ 366.756978] [<ffffffff81133780>] ? __pagevec_release+0x40/0x40
> [ 366.756986] [<ffffffff816776ca>] mutex_lock+0x2a/0x41
> [ 366.756991] [<ffffffff8104d19c>] get_online_cpus+0x2c/0x50
> [ 366.757000] [<ffffffff810693d9>] schedule_on_each_cpu+0x39/0x110
> [ 366.757008] [<ffffffff811337a5>] lru_add_drain_all+0x15/0x20
> [ 366.757016] [<ffffffff81150dd8>] SyS_mlock+0x38/0x130
> [ 366.757022] [<ffffffff816838c2>] system_call_fastpath+0x16/0x1b
>
>
>
> And that's why I am confused about how to solve it :)
>
> I thought when a CPU is going down its /sys/devices/system/cpu/cpuX/
> directory should be locked/freezed and no other thread should be reading
> from this directory at that point..
>
> @Srivatsa: Can you share your knowledge here on this?
>
Sorry for the late reply. I was on vacation for some time and it took
me a while to catch up on things.
Looking at the patches you have sent out, I think the first one[1] is
required, but the second one[2] isn't helpful. I have an alternative
fix that I'll propose as a reply to that thread.
Coming to the problem above, calling cpu_hotplug_disable/enable for
general hotplug synchronization is a bad idea. You must use
get/put_online_cpus() instead. I had sent out a patch to add a comment
pointing this out [3], but that didn't go upstream since it was part of
a larger patchset etc. Maybe I should break it out and send it separately.
And IMHO the kref_get race can be fixed by using get/put_online_cpus()
instead of your second patch[2].
[1]. https://patchwork.kernel.org/patch/2852463/
[2]. https://patchwork.kernel.org/patch/2852464/
[3]. https://patchwork.kernel.org/patch/2795771/
Regards,
Srivatsa S. Bhat
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