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

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Message-ID: <164576ab-4e68-ca5d-0c9e-d756588cdbb5@acm.org>
Date:   Thu, 1 Jun 2023 12:48:43 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com
Cc:     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 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(), 
isn't it?

Thanks,

Bart.