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SubjectRe: [RFC PATCH 06/19] cpufreq: always access cpufreq_policy_list while holding cpufreq_driver_lock
Hi,

On 12/01/16 15:27, Viresh Kumar wrote:
> On 11-01-16, 17:35, Juri Lelli wrote:
> > Commit highlights paths where we access cpufreq_policy_list without
> > holding cpufreq_driver_lock; one example being the following:
> >
> > [ 8.245779] ------------[ cut here ]------------
> > [ 8.305977] WARNING: CPU: 2 PID: 1 at kernel/drivers/cpufreq/cpufreq.c:2447 cpufreq_register_driver+0xfd/0x120()
> > [ 8.438611] Modules linked in:
> > [ 8.493751] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4+ #369
> > [ 8.561039] Hardware name: ARM-Versatile Express
> > [ 8.622765] [<c0014215>] (unwind_backtrace) from [<c0010e25>] (show_stack+0x11/0x14)
> > [ 8.629651] atkbd serio0: keyboard reset failed on 1c060000.kmi
> > [ 8.810905] [<c0010e25>] (show_stack) from [<c02ece7d>] (dump_stack+0x55/0x78)
> > [ 8.935122] [<c02ece7d>] (dump_stack) from [<c00202cd>] (warn_slowpath_common+0x59/0x84)
> > [ 9.067097] [<c00202cd>] (warn_slowpath_common) from [<c002030f>] (warn_slowpath_null+0x17/0x1c)
> > [ 9.204101] [<c002030f>] (warn_slowpath_null) from [<c03ba329>] (cpufreq_register_driver+0xfd/0x120)
> > [ 9.209603] usb 1-1.2: new high-speed USB device number 3 using isp1760
> > [ 9.419507] [<c03ba329>] (cpufreq_register_driver) from [<c03bc481>] (bL_cpufreq_register+0x49/0x98)
> > [ 9.560548] [<c03bc481>] (bL_cpufreq_register) from [<c0342517>] (platform_drv_probe+0x3b/0x6c)
> > [ 9.573806] usb-storage 1-1.2:1.0: USB Mass Storage device detected
> > [ 9.575468] scsi host0: usb-storage 1-1.2:1.0
> > [ 9.855845] [<c0342517>] (platform_drv_probe) from [<c03412e7>] (driver_probe_device+0x153/0x1bc)
> > [ 10.006137] [<c03412e7>] (driver_probe_device) from [<c03413a7>] (__driver_attach+0x57/0x58)
> > [ 10.009576] atkbd serio1: keyboard reset failed on 1c070000.kmi
> > [ 10.237057] [<c03413a7>] (__driver_attach) from [<c0340199>] (bus_for_each_dev+0x2d/0x4c)
> > [ 10.387824] [<c0340199>] (bus_for_each_dev) from [<c0340bd7>] (bus_add_driver+0xa3/0x14c)
> > [ 10.539200] [<c0340bd7>] (bus_add_driver) from [<c0341bff>] (driver_register+0x3b/0x88)
> > [ 10.691023] [<c0341bff>] (driver_register) from [<c0009613>] (do_one_initcall+0x5b/0x150)
> > [ 10.703809] scsi 0:0:0:0: Direct-Access General USB Flash Disk 1.0 PQ: 0 ANSI: 2
> > [ 10.713081] sd 0:0:0:0: [sda] 7831552 512-byte logical blocks: (4.00 GB/3.73 GiB)
> > [ 10.713973] sd 0:0:0:0: [sda] Write Protect is off
> > [ 10.713984] sd 0:0:0:0: [sda] Mode Sense: 03 00 00 00
> > [ 10.730783] sd 0:0:0:0: [sda] No Caching mode page found
> > [ 10.730814] sd 0:0:0:0: [sda] Assuming drive cache: write through
> > [ 10.779815] sda: sda1 sda2
> > [ 10.823590] sd 0:0:0:0: [sda] Attached SCSI removable disk
> > [ 11.581894] [<c0009613>] (do_one_initcall) from [<c0734b45>] (kernel_init_freeable+0x18d/0x22c)
> > [ 11.720454] [<c0734b45>] (kernel_init_freeable) from [<c04f45f9>] (kernel_init+0xd/0xa4)
> > [ 11.857340] [<c04f45f9>] (kernel_init) from [<c000dfb9>] (ret_from_fork+0x11/0x38)
> > [ 11.993082] ---[ end trace 62ff5522fb3f41dd ]---
> >
> > Fix this, and others, with proper locking of cpufreq_driver_lock.
>
> Perhaps this should be added prior to the lockdep patch, so that git
> bisect doesn't show lockdeps ?
>

I put patches in this order to be able to highlight problems before
fixing them. But I agree this is not nice for bisectability. I guess I
could squash related fixes and assertions together (when removing the
RFC tag) so that we don't break bisectability.

> > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > Cc: Viresh Kumar <viresh.kumar@linaro.org>
> > Signed-off-by: Juri Lelli <juri.lelli@arm.com>
> > ---
> > drivers/cpufreq/cpufreq.c | 13 ++++++++++++-
> > 1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 63d6efb..98adbc2 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -1585,6 +1585,7 @@ EXPORT_SYMBOL(cpufreq_generic_suspend);
> > void cpufreq_suspend(void)
> > {
> > struct cpufreq_policy *policy;
> > + unsigned long flags;
> >
> > if (!cpufreq_driver)
> > return;
> > @@ -1594,6 +1595,7 @@ void cpufreq_suspend(void)
> >
> > pr_debug("%s: Suspending Governors\n", __func__);
> >
> > + read_lock_irqsave(&cpufreq_driver_lock, flags);
> > for_each_active_policy(policy) {
> > if (__cpufreq_governor(policy, CPUFREQ_GOV_STOP))
> > pr_err("%s: Failed to stop governor for policy: %p\n",
> > @@ -1603,6 +1605,7 @@ void cpufreq_suspend(void)
> > pr_err("%s: Failed to suspend driver: %p\n", __func__,
> > policy);
> > }
> > + read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >
> > suspend:
> > cpufreq_suspended = true;
> > @@ -1617,6 +1620,7 @@ suspend:
> > void cpufreq_resume(void)
> > {
> > struct cpufreq_policy *policy;
> > + unsigned long flags;
> >
> > if (!cpufreq_driver)
> > return;
> > @@ -1628,6 +1632,7 @@ void cpufreq_resume(void)
> >
> > pr_debug("%s: Resuming Governors\n", __func__);
> >
> > + read_lock_irqsave(&cpufreq_driver_lock, flags);
> > for_each_active_policy(policy) {
> > if (cpufreq_driver->resume && cpufreq_driver->resume(policy))
> > pr_err("%s: Failed to resume driver: %p\n", __func__,
> > @@ -1637,6 +1642,7 @@ void cpufreq_resume(void)
> > pr_err("%s: Failed to start governor for policy: %p\n",
> > __func__, policy);
> > }
> > + read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >
> > /*
> > * schedule call cpufreq_update_policy() for first-online CPU, as that
> > @@ -2287,7 +2293,9 @@ static int cpufreq_boost_set_sw(int state)
> > struct cpufreq_frequency_table *freq_table;
> > struct cpufreq_policy *policy;
> > int ret = -EINVAL;
> > + unsigned long flags;
> >
> > + read_lock_irqsave(&cpufreq_driver_lock, flags);
> > for_each_active_policy(policy) {
> > freq_table = cpufreq_frequency_get_table(policy->cpu);
> > if (freq_table) {
> > @@ -2302,6 +2310,7 @@ static int cpufreq_boost_set_sw(int state)
> > __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
> > }
> > }
> > + read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >
> > return ret;
> > }
>
> For the above three, I am not sure if there can be some side effects.
> Can you please push a branch somewhere, to be tested by Fengguang's
> build bot? So that we know of any new lockdeps due to this? All above
> routines directly/indirectly call governor specific routines and that
> leads to freq-update in few cases. AFAIR, there were some issues with
> locking here.
>

I currently don't have any branch fetched by Fengguang's bot; I'll see
how to start doing that. In the meantime I'll try to setup an x86 box
and run some more tests.

> > @@ -2432,14 +2441,16 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
> > if (ret)
> > goto err_boost_unreg;
> >
> > - lockdep_assert_held(&cpufreq_driver_lock);
> > + read_lock_irqsave(&cpufreq_driver_lock, flags);
> > if (!(cpufreq_driver->flags & CPUFREQ_STICKY) &&
> > list_empty(&cpufreq_policy_list)) {
> > /* if all ->init() calls failed, unregister */
> > pr_debug("%s: No CPU initialized for driver %s\n", __func__,
> > driver_data->name);
> > + read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> > goto err_if_unreg;
> > }
> > + read_unlock_irqrestore(&cpufreq_driver_lock, flags);
>
> We have just registered the cpufreq driver, there is no other path
> that can simultaneously update the list here.
>
> And so we don't need the lock here.
>

I was thinking hotplug can get in the way, but we are inside a
{get,put}_online_cpus block. I'll remove that.

Thanks,

- Juri

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