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

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Message-ID: <204e13398c0b4c3d61786815e757e0bf@codeaurora.org>
Date:   Sat, 02 Jan 2021 21:10:52 +0800
From:   Can Guo <cang@...eaurora.org>
To:     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 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);
> }
> 
> Thanks,
> 
> Can Guo.