From: EJ Hsu <ejh@nvidia.com>
To: Oliver Neukum <oneukum@suse.com>, Alan Stern <stern@rowland.harvard.edu>
Cc: "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>
Subject: RE: [PATCH] usb: uas: fix a plug & unplug racing
Date: Wed, 22 Jan 2020 09:52:09 +0000 [thread overview]
Message-ID: <MN2PR12MB4126A6A761F168E03E751E5ACF0C0@MN2PR12MB4126.namprd12.prod.outlook.com> (raw)
In-Reply-To: <MN2PR12MB4126317E9BA1D269BE83E4EDCF0D0@MN2PR12MB4126.namprd12.prod.outlook.com>
EJ Hsu wrote:
> Oliver Neukum wrote:
>
> > > I just checked the code, and the reference count will be incremented
> > > in scsi_scan_host(), precisely speaking, in scsi_autopm_get_host().
> > > So, I still think we need to manually add reference count of interface here.
> > > Please correct me if there is anything wrong.
> >
> > AFAICT the generic power model will not suspend a parent while a child
> > is active. The includes SCSI children of USB parents. So I think we
> > are safe. Could you resubmit your patch without the PM counter
> > manipulation and we can fix any issue that may exist in theory later?
> >
>
> The child_count of usb device should be incremented in the scsi_scan_host().
> I can simulate this situation by forcibly enable the autosuspend of uas driver
> and add a delay before scsi_scan_host() is called in asynchronous way.
>
> But for now, as uas driver does not support autosuspend, it is indeed safe to
> remove the PM counter manipulation. If you have concern about it, it's OK to
> me to re-submit it.
>
By the way, if autosuspend will be enabled in uas driver in the future,
the PM counter manipulation should be added before scsi_add_host(),
just as MSC driver did. Otherwise, the child_count of usb device might be
accidentally decremented. (the rpm "idle" message will be propagated
from scsi host to usb interface and usb device)
Thanks,
EJ
--nvpublic
prev parent reply other threads:[~2020-01-22 9:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 3:30 [PATCH] usb: uas: fix a plug & unplug racing EJ Hsu
2020-01-13 9:44 ` Oliver Neukum
2020-01-13 15:21 ` Alan Stern
2020-01-14 3:28 ` EJ Hsu
2020-01-14 14:41 ` Oliver Neukum
2020-01-14 15:04 ` Alan Stern
2020-01-15 9:31 ` Oliver Neukum
2020-01-15 15:17 ` Alan Stern
2020-01-15 15:54 ` EJ Hsu
2020-01-20 9:38 ` Oliver Neukum
2020-01-21 11:29 ` EJ Hsu
2020-01-22 9:52 ` EJ Hsu [this message]
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