Message-ID: <fe8f6f37-2534-6481-cc34-e561b3b7a510@quicinc.com>
Date:   Tue, 14 Nov 2023 17:42:29 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     huangzaiyang <huangzaiyang@...o.com>, <myungjoo.ham@...sung.com>,
        <kyungmin.park@...sung.com>, <cw00.choi@...sung.com>
CC:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        huangzaiyang <joyyoung.wang@...il.com>
Subject: Re: [PATCH] Performance: devfreq: avoid devfreq delay work re-init
 before



On 11/10/2023 3:04 PM, huangzaiyang wrote:
> From: huangzaiyang <joyyoung.wang@...il.com>
> 
> There is a timer_list race condition when executing the following test shell script:
> '''
> while true
> do
>          echo "simple_ondemand" > /sys/class/devfreq/1d84000.ufshc/governor
>          echo "performance" > /sys/class/devfreq/1d84000.ufshc/governor
> done
> '''
> 
> [13511.214366][    C3] Unable to handle kernel paging request at virtual address dead00000000012a
> [13511.214393][    C3] Mem abort info:
> [13511.214398][    C3]   ESR = 0x96000044
> [13511.214404][    C3]   EC = 0x25: DABT (current EL), IL = 32 bits
> [13511.214409][    C3]   SET = 0, FnV = 0
> [13511.214414][    C3]   EA = 0, S1PTW = 0
> [13511.214417][    C3] Data abort info:
> [13511.214422][    C3]   ISV = 0, ISS = 0x00000044
> [13511.214427][    C3]   CM = 0, WnR = 1
> [13511.214432][    C3] [dead00000000012a] address between user and kernel address ranges
> [13511.214439][    C3] Internal error: Oops: 96000044 [#1] PREEMPT SMP
> [13511.215449][    C3] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G S      W  O      5.10.168-android12-9-o-g63cc297a7b34 #1
> [13511.215454][    C3] Hardware name: Qualcomm Technologies, Inc. Cape MTP, Whiteswan (DT)
> [13511.215460][    C3] pstate: 82400085 (Nzcv daIf +PAN -UAO +TCO BTYPE=--)
> [13511.215472][    C3] pc : expire_timers+0x9c/0x428
> [13511.215478][    C3] lr : __run_timers+0x1f0/0x328
> [13511.215483][    C3] sp : ffffffc00801bdd0
> [13511.215487][    C3] x29: ffffffc00801bdf0 x28: ffffffdb87b31698
> [13511.215493][    C3] x27: ffffffdb87999e58 x26: ffffffdb87966008
> [13511.215499][    C3] x25: 0000000000000001 x24: ffffff8001734a00
> [13511.215506][    C3] x23: 00000000000000e0 x22: dead000000000122
> [13511.215512][    C3] x21: 000000010032658e x20: ffffff89f7a9ae80
> [13511.215518][    C3] x19: ffffffc00801be50 x18: ffffffc00801d038
> [13511.215525][    C3] x17: 0000000000000240 x16: 0000000000000201
> [13511.215532][    C3] x15: ffffffffffffffff x14: ffffff89f7a9aef8
> [13511.215538][    C3] x13: 0000000000000240 x12: ffffff89f7a9aea8
> [13511.215544][    C3] x11: 0000000000000021 x10: 000000014032658e
> [13511.215550][    C3] x9 : ffffffc00801be50 x8 : dead000000000122
> [13511.215556][    C3] x7 : ffff71646c68735e x6 : ffffff89f7aaae58
> [13511.215563][    C3] x5 : 0000000000000000 x4 : 0000000000000101
> [13511.215569][    C3] x3 : ffffff89f7a9aef0 x2 : ffffff89f7a9aef0
> [13511.215575][    C3] x1 : ffffffc00801be50 x0 : ffffff8045804428
> [13511.215581][    C3] Call trace:
> [13511.215586][    C3]  expire_timers+0x9c/0x428
> [13511.215591][    C3]  __run_timers+0x1f0/0x328
> [13511.215596][    C3]  run_timer_softirq+0x28/0x58
> [13511.215602][    C3]  efi_header_end+0x168/0x5ec
> [13511.215610][    C3]  __irq_exit_rcu+0x108/0x124
> [13511.215617][    C3]  __handle_domain_irq+0x118/0x1e4
> [13511.215625][    C3]  gic_handle_irq.31230+0x6c/0x250
> [13511.215630][    C3]  el1_irq+0xe4/0x1c0
> [13511.215638][    C3]  cpuidle_enter_state+0x3a4/0xa04
> [13511.215644][    C3]  do_idle+0x308/0x574
> [13511.215649][    C3]  cpu_startup_entry+0x84/0x90
> [13511.215656][    C3]  secondary_start_kernel+0x204/0x274
> [13511.215664][    C3] Code: d503201f a9402408 f9000128 b4000048 (f9000509)
> [13511.215670][    C3] ---[ end trace 5100bad72a35d566 ]---
> [13511.215676][    C3] Kernel panic - not syncing: Oops: Fatal exception in interrupt
> 
> This is because when switching the governor through the sys node,
> the devfreq_monitor_start function will re-initialize the delayed work task,
> which will cause the delay work pending flag to become invalid, and the timer pending judgment contained in the delayed work will also become invalid,
> and then the pending interception will be executed when the queue is executed.
> 
> So we remove the delay work'initialization work to the devfreq_add_device and timer_store functions,
> and the delay work pending judgment is performed before the devfreq_monitor_start function performs the queue operation.
> 
> Signed-off-by: ZaiYang Huang <huangzaiyang@...o.com>
> ---
>   drivers/devfreq/devfreq.c | 36 ++++++++++++++++++++++++------------
>   1 file changed, 24 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index b3a68d5833bd..8ae6f853a21e 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -483,18 +483,7 @@ void devfreq_monitor_start(struct devfreq *devfreq)
>          if (IS_SUPPORTED_FLAG(devfreq->governor->flags, IRQ_DRIVEN))
>                  return;
> 
> -       switch (devfreq->profile->timer) {
> -       case DEVFREQ_TIMER_DEFERRABLE:
> -               INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
> -               break;
> -       case DEVFREQ_TIMER_DELAYED:
> -               INIT_DELAYED_WORK(&devfreq->work, devfreq_monitor);
> -               break;
> -       default:
> -               return;
> -       }
> -
> -       if (devfreq->profile->polling_ms)
> +       if (devfreq->profile->polling_ms && !delayed_work_pending(&devfreq->work))
>                  queue_delayed_work(devfreq_wq, &devfreq->work,
>                          msecs_to_jiffies(devfreq->profile->polling_ms));
>   }
> @@ -830,6 +819,17 @@ struct devfreq *devfreq_add_device(struct device *dev,
>                  goto err_dev;
>          }
> 
> +       switch (devfreq->profile->timer) {
> +       case DEVFREQ_TIMER_DEFERRABLE:
> +               INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
> +               break;
> +       case DEVFREQ_TIMER_DELAYED:
> +               INIT_DELAYED_WORK(&devfreq->work, devfreq_monitor);
> +               break;
> +       default:
> +               dev_err(dev, "%s: Target devfreq(%s)'s profile timer has no settings \n", devfreq->governor_name,
> +                       __func__);
> +       }

[..]

>          if (!devfreq->profile->max_state || !devfreq->profile->freq_table) {
>                  mutex_unlock(&devfreq->lock);
>                  err = set_freq_table(devfreq);
> @@ -1860,6 +1860,18 @@ static ssize_t timer_store(struct device *dev, struct device_attribute *attr,
>          df->profile->timer = timer;
>          mutex_unlock(&df->lock);
> 
> +       switch (df->profile->timer) {
> +       case DEVFREQ_TIMER_DEFERRABLE:
> +               INIT_DEFERRABLE_WORK(&df->work, devfreq_monitor);
> +               break;
> +       case DEVFREQ_TIMER_DELAYED:
> +               INIT_DELAYED_WORK(&df->work, devfreq_monitor);
> +               break;
> +       default:
> +               dev_err(dev, "%s: Target devfreq(%s)'s profile timer has no settings \n", df->governor_name,
> +                       __func__);
> +       }
> +
Here, this can cause issue right, as it is modifying the delayed work
data even before stopping the current running instances..

Should the above thing be done after DEVFREQ_GOV_STOP ?
But again it will boil down to the same thing as it is currently
now .
>          ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
>          if (ret) {
>                  dev_warn(dev, "%s: Governor %s not stopped(%d)\n",

I was thinking if i put mutex around cancel_delayed_work_sync() as well 
in devfreq_monitor_stop() on top of below patch, should cover the 
corruption of workdata.

https://lore.kernel.org/all/1699957648-31299-1-git-send-email-quic_mojha@quicinc.com/

-Mukesh

> --
> 2.17.1

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