linux-kernel - Re: [PATCH v2 1/2] scsi: ufs: Fix a possible NULL pointer issue

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Message-ID: <8dea503d-9ab7-c003-9ade-3470def21764@intel.com>
Date:   Fri, 15 Jan 2021 15:07:25 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Can Guo <cang@...eaurora.org>, Bart Van Assche <bvanassche@....org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, ziqichen@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] scsi: ufs: Fix a possible NULL pointer issue

On 2/01/21 3:10 pm, Can Guo wrote:
> On 2021-01-02 20:29, Can Guo wrote:
>> On 2021-01-02 00:05, Bart Van Assche wrote:
>>> On 12/31/20 9:44 PM, Can Guo wrote:
>>>> During system resume/suspend, hba could be NULL. In this case, do not touch
>>>> eh_sem.
>>>>
>>>> Fixes: 88a92d6ae4fe ("scsi: ufs: Serialize eh_work with system PM events
>>>> and async scan")
>>>>
>>>> Signed-off-by: Can Guo <cang@...eaurora.org>
>>>> ---
>>>>  drivers/scsi/ufs/ufshcd.c | 9 +++++----
>>>>  1 file changed, 5 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>>>> index e221add..34e2541 100644
>>>> --- a/drivers/scsi/ufs/ufshcd.c
>>>> +++ b/drivers/scsi/ufs/ufshcd.c
>>>> @@ -8896,8 +8896,11 @@ int ufshcd_system_suspend(struct ufs_hba *hba)
>>>>      int ret = 0;
>>>>      ktime_t start = ktime_get();
>>>>
>>>> +    if (!hba)
>>>> +        return 0;
>>>> +
>>>>      down(&hba->eh_sem);
>>>> -    if (!hba || !hba->is_powered)
>>>> +    if (!hba->is_powered)
>>>>          return 0;
>>>>
>>>>      if ((ufs_get_pm_lvl_to_dev_pwr_mode(hba->spm_lvl) ==
>>>> @@ -8945,10 +8948,8 @@ int ufshcd_system_resume(struct ufs_hba *hba)
>>>>      int ret = 0;
>>>>      ktime_t start = ktime_get();
>>>>
>>>> -    if (!hba) {
>>>> -        up(&hba->eh_sem);
>>>> +    if (!hba)
>>>>          return -EINVAL;
>>>> -    }
>>>>
>>>>      if (!hba->is_powered || pm_runtime_suspended(hba->dev))
>>>>          /*
>>>
>>> Hi Can,
>>>
>>> How can ufshcd_system_suspend() or ufshcd_system_resume() be called with a
>>> NULL argument? In ufshcd_pci_probe() I see that pci_set_drvdata() is called
>>> before pm_runtime_allow(). ufshcd_pci_remove() calls pm_runtime_forbid().
>>>
>>> Thanks,
>>>
>>> Bart.
>>
>> Hi Bart,
>>
>> You are right about ufshcd_RUNTIME_suspend/resume() - platform_set_drvdata()
>> is called before pm_runtime_enable(), so runtime suspend/resume cannot happen
>> before pm_runtime_enable() is called. We can remove the sanity checks of
>> !hba there, they are outdated.
> 
> Add more history here - before Stanley's change (see below),
> platform_set_drvdata()
> is called AFTER pm_runtime_enable(), which was why we needed sanity checks
> of !hba.
> But now the sanity checks are unnecessary in
> ufshcd_RUNTIME_suspend/resume(), so
> feel free to remove them.
> 
> But still, things are a bit different for ufshcd_SYSTEM_suspend/resume(), we
> need
> the sanity checks of !hba there if my understanding is correct.
> 
> commit 24e2e7a19f7e4b83d0d5189040d997bce3596473
> Author: Stanley Chu <stanley.chu@...iatek.com>
> Date:   Wed Jun 12 23:19:05 2019 +0800
> 
>     scsi: ufs: Avoid runtime suspend possibly being blocked forever
> 
> Thanks,
> Can Guo.
> 
>>
>> But for ufshcd_SYSTEM_suspend/resume() callbacks (not runtime ones), my
>> understanding is that system suspend/resume may happen after probe (vendor
>> driver probe calls ufshcd_pltfrm_init()) starts but before
>> platform_set_drvdata()
>> is called, in this case hba is NULL.
>>
>> int ufshcd_pltfrm_init(struct platform_device *pdev,
>>                const struct ufs_hba_variant_ops *vops)
>> {
>> ...
>>      platform_set_drvdata(pdev, hba);
>>
>>     pm_runtime_set_active(&pdev->dev);
>>     pm_runtime_enable(&pdev->dev);
>> }

Hi Can

I expect probe and system suspend are synchronized e.g. by device_lock(), so
hba would not be NULL.  Is there any example of it being NULL in system suspend?

Regards
Adrian