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

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Date:   Tue, 12 Jan 2021 14:35:27 +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 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?

Thanks a lot.
Stanley Chu

>  
>  	if (!hba->is_powered || pm_runtime_suspended(hba->dev))