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SubjectRe: [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@codeaurora.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 !hba there, they are outdated.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@mediatek.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.

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