linux-kernel - Re: [PATCH v5] scsi: core: Wait until device is fully resumed before doing rescan

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Date:   Fri, 2 Jun 2023 09:00:51 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Bart Van Assche <bvanassche@....org>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com, dlemoal@...nel.org,
        bblock@...ux.ibm.com, acelan.kao@...onical.com,
        linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] scsi: core: Wait until device is fully resumed before
 doing rescan

On Fri, Jun 2, 2023 at 3:48 AM Bart Van Assche <bvanassche@....org> wrote:
>
> On 6/1/23 08:56, Kai-Heng Feng wrote:
> > During system resuming process, the resuming order is from top to down.
> > Namely, the ATA host is resumed before disks connected to it.
> >
> > When an EH is scheduled while ATA host is resumed and disk device is
> > still suspended, the device_lock hold by scsi_rescan_device() is never
> > released so the dpm_resume() of the disk is blocked forerver, therefore
> > the system can never be resumed back.
> >
> > 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, wait until the scsi device is fully resumed,
> > before continuing the rescan process.
>
> Why doesn't scsi_attach_vpd() support runtime power management? Calling
> scsi_attach_vpd() should result in a call of sdev_runtime_resume(),

It's system-wide resume in this context, so it's dpm_resume() waiting
for the lock to be released by scsi_rescan_device().

Kai-Heng

> isn't it?
>
> Thanks,
>
> Bart.
>