Re: [PATCH v2 2/4] cpufreq: qcom-hw: fix the race between LMH worker and cpuhp

Vladimir Zapolskiy
2022-03-17T23:10:41Z

Hi Dmitry,

On 3/10/22 12:39 AM, Dmitry Baryshkov wrote:
> qcom_lmh_dcvs_poll() can be running when the cpu is being put offline.
> This results in the following warnings and an oops. The driver would
> disable the worker, but it happens closer to the end of
> cpufreq_offline(). Change the locking in the qcom_lmh_dcvs_poll(), so
> that the worker can not run in parallel with cpufreq_offline() call.
>
> [ 55.650435] (NULL device *): dev_pm_opp_find_freq_floor: Invalid argument freq=00000000709ccbf9
> [ 55.659420] (NULL device *): Can't find the OPP for throttling: -EINVAL!
> [ 55.666329] Unable to handle kernel paging request at virtual address ffffadfba4bb6d81
> [ 55.674491] Mem abort info:
> [ 55.677363] ESR = 0x96000004
> [ 55.680527] EC = 0x25: DABT (current EL), IL = 32 bits
> [ 55.686001] SET = 0, FnV = 0
> [ 55.689164] EA = 0, S1PTW = 0
> [ 55.692418] FSC = 0x04: level 0 translation fault
> [ 55.697449] Data abort info:
> [ 55.700426] ISV = 0, ISS = 0x00000004
> [ 55.704383] CM = 0, WnR = 0
> [ 55.707455] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000a98e9000
> [ 55.714354] [ffffadfba4bb6d81] pgd=0000000000000000, p4d=0000000000000000
> [ 55.721388] Internal error: Oops: 96000004 [#1] SMP
> [ 55.726397] Modules linked in:
> [ 55.729542] CPU: 7 PID: 162 Comm: kworker/7:1H Tainted: G S W 5.17.0-rc6-00100-g04890a1d9672 #724
> [ 55.746066] Workqueue: events_highpri qcom_lmh_dcvs_poll
> [ 55.751527] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [ 55.758669] pc : cpufreq_cpu_get_raw+0x20/0x44
> [ 55.763233] lr : qcom_cpufreq_hw_get+0x10/0x64
> [ 55.767799] sp : ffff800009983d10
> [ 55.771207] x29: ffff800009983d10 x28: ffffaa13a4f2b000 x27: ffff7b31329f9305
> [ 55.778530] x26: ffffaa13a4f30af8 x25: ffffaa13a4f4e4c8 x24: ffff7b2ec2eda000
> [ 55.785851] x23: ffffffffffffffea x22: ffff7b2ec2e9fc18 x21: ffff7b2ec2e9fc00
> [ 55.793170] x20: 0000000000000100 x19: ffff7b2ec2e9fcc0 x18: ffffffffffffffff
> [ 55.800490] x17: 726620746e656d75 x16: 6772612064696c61 x15: ffff8000899839c7
> [ 55.807812] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
> [ 55.815140] x11: ffff7b2ec2e9fc80 x10: ffffaa13a59a1a70 x9 : 0000000000000000
> [ 55.822468] x8 : ffff7b2eca6917c0 x7 : ffffaa13a528b000 x6 : 0000000000000001
> [ 55.829788] x5 : 0000000000040000 x4 : 000000000000024f x3 : 0000000000000000
> [ 55.837116] x2 : 0000000000000100 x1 : ffffaa13a4bb6d80 x0 : 000003e800000001
> [ 55.844439] Call trace:
> [ 55.846951] cpufreq_cpu_get_raw+0x20/0x44
> [ 55.851155] qcom_lmh_dcvs_poll+0x104/0x160
> [ 55.855452] process_one_work+0x288/0x69c
> [ 55.859574] worker_thread+0x74/0x470
> [ 55.863336] kthread+0xfc/0x100
> [ 55.866568] ret_from_fork+0x10/0x20
> [ 55.870246] Code: b00065c1 91360021 d503233f f8625800 (f8616800)
> [ 55.876501] ---[ end trace 0000000000000000 ]---
>
> Fixes: 275157b367f4 ("cpufreq: qcom-cpufreq-hw: Add dcvs interrupt support")
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> ---
> drivers/cpufreq/qcom-cpufreq-hw.c | 24 +++++++++++++++++++++---
> 1 file changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
> index 44d46e52baea..7c1bb002e1c3 100644
> --- a/drivers/cpufreq/qcom-cpufreq-hw.c
> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> @@ -296,6 +296,23 @@ static void qcom_lmh_dcvs_notify(struct qcom_cpufreq_data *data)
> struct dev_pm_opp *opp;
> unsigned int freq;
>
> + /*
> + * Synchronize against CPU going offline.
> + * cpufreq_offline() will get the write lock on policy->rwsem.
> + */
> +retry:
> + if (unlikely(!down_read_trylock(&policy->rwsem))) {
> + mutex_lock(&data->throttle_lock);
> + if (data->cancel_throttle) {
> + mutex_unlock(&data->throttle_lock);
> + return;
> + }
> +
> + mutex_unlock(&data->throttle_lock);
> +
> + schedule();
> + goto retry;
> + }

do you see an option here to base the logic on policy->cpus mask value instead of
the semaphore lock status? I believe it should be possible, and, if so, likely
it would be preferable.

> /*
> * Get the h/w throttled frequency, normalize it using the
> * registered opp table and use it to calculate thermal pressure.
> @@ -314,9 +331,10 @@ static void qcom_lmh_dcvs_notify(struct qcom_cpufreq_data *data)
>
> /*
> * In the unlikely case policy is unregistered do not enable
> - * polling or h/w interrupt
> + * polling or h/w interrupt.
> + * If we are here, we have the policy->rwsem read lock,
> + * cancel_throttle can be toggled only with the write lock.
> */
> - mutex_lock(&data->throttle_lock);
> if (data->cancel_throttle)
> goto out;
>
> @@ -331,7 +349,7 @@ static void qcom_lmh_dcvs_notify(struct qcom_cpufreq_data *data)
> msecs_to_jiffies(10));
>
> out:
> - mutex_unlock(&data->throttle_lock);
> + up_read(&policy->rwsem);
> }
>
> static void qcom_lmh_dcvs_poll(struct work_struct *work)
>

FWIW I can add my:

Tested-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>

--
Best wishes,
Vladimir