linux-kernel - Re: [bug report] scsi: SATA devices missing after FLR is triggered during HBA suspended

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Date: Wed, 26 Jun 2024 10:15:46 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Damien Le Moal <dlemoal@...nel.org>
Cc: Yihang Li <liyihang9@...wei.com>, cassel@...nel.org,
	James.Bottomley@...senpartnership.com, martin.petersen@...cle.com,
	john.g.garry@...cle.com, yanaijie@...wei.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linuxarm@...wei.com, chenxiang66@...ilicon.com,
	prime.zeng@...wei.com,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [bug report] scsi: SATA devices missing after FLR is triggered
 during HBA suspended

On Mon, Jun 24, 2024 at 09:10:41AM +0900, Damien Le Moal wrote:
> On 6/22/24 12:31 PM, Yihang Li wrote:
> > Hi Damien,
> > 
> > Thanks for your reply.
> > 
> > On 2024/6/19 7:11, Damien Le Moal wrote:
> >> On 6/18/24 22:29, Yihang Li wrote:
> >>> Hi Damien,
> >>>
> >>> I found out that two issues is caused by commit 0c76106cb975 ("scsi: sd:
> >>> Fix TCG OPAL unlock on system resume") and 626b13f015e0 ("scsi: Do not
> >>> rescan devices with a suspended queue").
> >>>
> >>> The two issues as follows for the situation that there are ATA disks
> >>> connected with SAS controller:
> >>
> >> Which controller ? What is the driver ?
> > 
> > I'm using the hisi_sas_v3_hw driver and it supports HiSilicon's SAS controller.
> 
> I do not have access to this HBA, but I have one that uses libsas/pm8001 driver
> so I will try to test with that.
> 
> >>> (1) FLR is triggered after all disks and controller are suspended. As a
> >>> result, the number of disks is abnormal.
> >>
> >> I am assuming here that FLR means PCI "Function Level Reset" ?
> > 
> > Yes, I am talking about the PCI "Function Level Reset"
> > 
> >> FLR and disk/controller suspend execution timing are unrelated. FLR can be
> >> triggered at any time through sysfs. So please give details here. Why is FLR
> >> done when the system is being suspended ?
> > 
> > Yes, it is because FLR can be triggered at any time that we are testing the
> > reliability of executing FLR commands after disk/controller suspended.
> 
> "can be triggered" ? FLR is not a random asynchronous event. It is an action
> that is *issued* by a user with sys admin rights. And such users can do a lot
> of things that can break a machine...
> 
> I fail to see the point of doing a function reset while the device is
> suspended. But granted, I guess the device should comeback up in such case,
> though I would like to hear what the PCI guys have to say about this.
> 
> Bjorn,
> 
> Is reseting a suspended PCI device something that should be/is supported ?

I doubt it.  The PCI core should be preserving all the generic PCI
state across suspend/resume.  The driver should only need to
save/restore device-specific things the PCI core doesn't know about.

A reset will clear out most state, and the driver doesn't know the
reset happened, so it will expect most device state to have been
preserved.

Bjorn