linux-kernel - Re: [PATCH] scsi: core: Avoid doing rescan on suspended device

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Date:   Thu, 20 Apr 2023 17:43:21 +0000
From:   Benjamin Block <bblock@...ux.ibm.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com,
        acelan.kao@...onical.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: core: Avoid doing rescan on suspended device

On Wed, Apr 19, 2023 at 01:41:12PM +0800, Kai-Heng Feng wrote:
> During system resume, if an EH is schduled after ATA host is resumed
> (i.e. ATA_PFLAG_PM_PENDING cleared), but before the disk device is
> resumed, the device_lock hold by scsi_rescan_device() is never released
> so the dpm_resume() of the disk is blocked forerver.
> 
> That's because scsi_attach_vpd() is expecting the disk device is in
> operational state, as it doesn't work on suspended device.
> 
> To avoid such deadlock, avoid doing rescan if the disk is still
> suspended so the resume process of the disk device can proceed.

I'm no expert on suspend/resume, but wouldn't you then potentially miss
changes that have been done to the LUN during suspend?

What takes care of updating the VPDs, scsi-disk re-evaluation and such
in this case, when you block it initially during wakeup?

> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/scsi/scsi_scan.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index d217be323cc6..36680cb1535b 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -1621,6 +1621,9 @@ void scsi_rescan_device(struct device *dev)
>  {
>  	struct scsi_device *sdev = to_scsi_device(dev);
>  
> +	if (dev->power.is_prepared)
> +		return;
> +
>  	device_lock(dev);
>  
>  	scsi_attach_vpd(sdev);
> -- 
> 2.34.1
> 

-- 
Best Regards, Benjamin Block        /        Linux on IBM Z Kernel Development
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