Re: [PATCH] PM / devfreq: Add missing locking while setting suspend_freq

[Leonard Crestez]

On 13.11.2019 04:11, Chanwoo Choi wrote:
> Dear Rafael,
> 
> Could you take this patch directly into linux-pm.git for v5.5-rc1?
> 
> Because the devfreq pull-request for v5.5-rc1 contained issue. This patch
> fix the issue of following patch[1].
> [1] https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Frafael%2Flinux-pm.git%2Fcommit%2F%3Fh%3Dlinux-next%26id%3D2abb0d5268ae7b5ddf82099b1f8d5aa8414637d4&data=02%7C01%7Cleonard.crestez%40nxp.com%7C7f8b7da8a0db4c0c80c208d767ded288%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637092079037128803&sdata=YW2zd3rpgphZtrhUfrA0wOTU10Ee0vDdEtcphKtGS3U%3D&reserved=0
> 
> 
> ---
> Hi Marek,
> 
> Thanks for the fixup.
> Acked-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
> 
> Regards,
> Chanwoo Choi
> 
> 
> On 11/12/19 7:47 PM, Marek Szyprowski wrote:
>> Commit 2abb0d5268ae ("PM / devfreq: Lock devfreq in trans_stat_show")
>> revealed a missing locking while calling devfreq_update_status() function
>> during suspend/resume cycle.
>>
>> Code analysis revealed that devfreq_set_target() function was called
>> without needed locks held for setting device specific suspend_freq if such
>> has been defined. This patch fixes that by adding the needed locking, what
>> fixes following kernel warning on Exynos4412-based OdroidU3 board during
>> system suspend:

I think that devfreq_suspend always need the lock, this issue was just 
exposed by adding a lock assertion in devfreq_update_status.

There was a rare but real race condition here between "set_target" and 
suspend.

>> PM: suspend entry (deep)
>> Filesystems sync: 0.002 seconds
>> Freezing user space processes ... (elapsed 0.001 seconds) done.
>> OOM killer disabled.
>> Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
>> ------------[ cut here ]------------
>> WARNING: CPU: 2 PID: 1385 at drivers/devfreq/devfreq.c:204 devfreq_update_status+0xc0/0x188
>> Modules linked in:
>> CPU: 2 PID: 1385 Comm: rtcwake Not tainted 5.4.0-rc6-next-20191111 #6848
>> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
>> [<c0112588>] (unwind_backtrace) from [<c010e070>] (show_stack+0x10/0x14)
>> [<c010e070>] (show_stack) from [<c0afb010>] (dump_stack+0xb4/0xe0)
>> [<c0afb010>] (dump_stack) from [<c01272e0>] (__warn+0xf4/0x10c)
>> [<c01272e0>] (__warn) from [<c01273a8>] (warn_slowpath_fmt+0xb0/0xb8)
>> [<c01273a8>] (warn_slowpath_fmt) from [<c07d105c>] (devfreq_update_status+0xc0/0x188)
>> [<c07d105c>] (devfreq_update_status) from [<c07d2d70>] (devfreq_set_target+0xb0/0x15c)
>> [<c07d2d70>] (devfreq_set_target) from [<c07d3598>] (devfreq_suspend+0x2c/0x64)
>> [<c07d3598>] (devfreq_suspend) from [<c05de0b0>] (dpm_suspend+0xa4/0x57c)
>> [<c05de0b0>] (dpm_suspend) from [<c05def74>] (dpm_suspend_start+0x98/0xa0)
>> [<c05def74>] (dpm_suspend_start) from [<c0195b58>] (suspend_devices_and_enter+0xec/0xc74)
>> [<c0195b58>] (suspend_devices_and_enter) from [<c0196a20>] (pm_suspend+0x340/0x410)
>> [<c0196a20>] (pm_suspend) from [<c019480c>] (state_store+0x6c/0xc8)
>> [<c019480c>] (state_store) from [<c033fc50>] (kernfs_fop_write+0x10c/0x228)
>> [<c033fc50>] (kernfs_fop_write) from [<c02a6d3c>] (__vfs_write+0x30/0x1d0)
>> [<c02a6d3c>] (__vfs_write) from [<c02a9afc>] (vfs_write+0xa4/0x180)
>> [<c02a9afc>] (vfs_write) from [<c02a9d58>] (ksys_write+0x60/0xd8)
>> [<c02a9d58>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
>> Exception stack(0xed3d7fa8 to 0xed3d7ff0)
>> ...
>> irq event stamp: 9667
>> hardirqs last  enabled at (9679): [<c0b1e7c4>] _raw_spin_unlock_irq+0x20/0x58
>> hardirqs last disabled at (9698): [<c0b16a20>] __schedule+0xd8/0x818
>> softirqs last  enabled at (9694): [<c01026fc>] __do_softirq+0x4fc/0x5fc
>> softirqs last disabled at (9719): [<c012fe68>] irq_exit+0x16c/0x170
>> ---[ end trace 41ac5b57d046bdbc ]---
>> ------------[ cut here ]------------
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>> ---
>>   drivers/devfreq/devfreq.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 94fb8e821e12..65a4b6cf3fa5 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -957,7 +957,9 @@ int devfreq_suspend_device(struct devfreq *devfreq)
>>   	}
>>   
>>   	if (devfreq->suspend_freq) {
>> +		mutex_lock(&devfreq->lock);
>>   		ret = devfreq_set_target(devfreq, devfreq->suspend_freq, 0);
>> +		mutex_unlock(&devfreq->lock);
>>   		if (ret)
>>   			return ret;
>>   	}
>> @@ -985,7 +987,9 @@ int devfreq_resume_device(struct devfreq *devfreq)
>>   		return 0;
>>   
>>   	if (devfreq->resume_freq) {
>> +		mutex_lock(&devfreq->lock);
>>   		ret = devfreq_set_target(devfreq, devfreq->resume_freq, 0);
>> +		mutex_unlock(&devfreq->lock);
>>   		if (ret)
>>   			return ret;
>>   	}
>>
> 
>