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From: Oliver Neukum <oneukum@suse.com>
To: EJ Hsu <ejh@nvidia.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: Mon, 20 Jan 2020 10:38:34 +0100	[thread overview]
Message-ID: <1579513114.17973.13.camel@suse.com> (raw)
In-Reply-To: <MN2PR12MB41262435500D3FC463DBFC32CF370@MN2PR12MB4126.namprd12.prod.outlook.com>

Am Mittwoch, den 15.01.2020, 15:54 +0000 schrieb EJ Hsu:

Hi,

> That's another reason why I would like to run scsi_scan_host() asynchronously
> and keep the hub thread free.

Very well. I must say I don't like it, but I have no good alternative.

> > > In my opinion, if scsi_scan_host() will be run asynchronously, this 
> > > interface needs to be guarded against runtime PM between uas_probe() & uas_scan_work().
> > 
> > Yes it does. But it has a child, the SCSI host, which has an elevated count. It is already guarded.
> 
> 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?

	Regards
		Oliver


  reply	other threads:[~2020-01-20  9:38 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 [this message]
2020-01-21 11:29               ` EJ Hsu
2020-01-22  9:52                 ` EJ Hsu

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