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References: <20230419054112.269734-1-kai.heng.feng@canonical.com> <20230420174321.GA123094@t480-pf1aa2c2>
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From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
Date:   Mon, 24 Apr 2023 11:30:01 +0800
Message-ID: <CAAd53p4+7npE=Q1eWeNZp01F0BukKHj8inx95_ektv_zkvtjqw@mail.gmail.com>
Subject: Re: [PATCH] scsi: core: Avoid doing rescan on suspended device
To:     Benjamin Block <bblock@linux.ibm.com>
Cc:     jejb@linux.ibm.com, martin.petersen@oracle.com,
        acelan.kao@canonical.com, linux-scsi@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Fri, Apr 21, 2023 at 1:43=E2=80=AFAM Benjamin Block <bblock@linux.ibm.co=
m> wrote:
>
> 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?

This is a valid concern.

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

The other approach is to perform the re-evaluation when the system
resume is about to be completed.
Let me send v2 to address that.


Kai-Heng

>
> >
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.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 =3D 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 Develo=
pment
> IBM Deutschland Research & Development GmbH    /   https://www.ibm.com/pr=
ivacy
> Vors. Aufs.-R.: Gregor Pillen         /         Gesch=C3=A4ftsf=C3=BChrun=
g: David Faller
> Sitz der Ges.: B=C3=B6blingen     /    Registergericht: AmtsG Stuttgart, =
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