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

[Can Guo]

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@xxxxxxxxxxxxxx>
> > > ---
> > >  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 !hba there, they are outdated.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@xxxxxxxxxxxx>
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.