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

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Date:   Tue, 12 Jan 2021 14:52:13 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
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>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] scsi: ufs: Fix a possible NULL pointer issue

On 2021-01-12 14:35, Stanley Chu wrote:
> Hi Can,
> 
> On Sat, 2021-01-02 at 05:59 -0800, 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>
>> 
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index e221add..9829c8d 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -94,6 +94,8 @@
>>  		       16, 4, buf, __len, false);                        \
>>  } while (0)
>> 
>> +static bool early_suspend;
>> +
>>  int ufshcd_dump_regs(struct ufs_hba *hba, size_t offset, size_t len,
>>  		     const char *prefix)
>>  {
>> @@ -8896,8 +8898,14 @@ int ufshcd_system_suspend(struct ufs_hba *hba)
>>  	int ret = 0;
>>  	ktime_t start = ktime_get();
>> 
>> +	if (!hba) {
>> +		early_suspend = true;
>> +		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) ==
>> @@ -8945,9 +8953,12 @@ 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 (unlikely(early_suspend)) {
>> +		early_suspend = false;
>> +		down(&hba->eh_sem);
>>  	}
> 
> I guess early_suspend here is to handle the case that hba is null 
> during
> ufshcd_system_suspend() but !null during ufshcd_system_resume(). If 
> yes,
> would it be possible? If no, may I know what is the purpose?
> 

Yes, you are right. I think it is possible. platform_set_drvdata()
is called in ufshcd_pltfrm_init(). Say suspend happens before
platform_set_drvdata() is called, but resume comes back after
platform_set_drvdata() is called. What do you think?

Thanks,
Can Guo.

> Thanks a lot.
> Stanley Chu
> 
>> 
>>  	if (!hba->is_powered || pm_runtime_suspended(hba->dev))