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

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Date:   Tue, 12 Jan 2021 17:17:15 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Can Guo <cang@...eaurora.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>,
        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

Hi Can,

On Tue, 2021-01-12 at 14:52 +0800, Can Guo wrote:
> 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 for remind. After looking into system suspend flow, kernel thread
may continue running even after UFS suspend callback is executed by
suspend flow.

Feel free to add
Acked-by: Stanley Chu <stanley.chu@...iatek.com>