linux-kernel - Re: [PATCH v3 2/6] PM / Runtime: introduce pm_runtime_set[get]_memalloc

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Message-ID: <2504263.kbM6W9JoH9@linux-lqwf.site>
Date:	Tue, 30 Oct 2012 17:30:13 +0100
From:	Oliver Neukum <oneukum@...e.de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Jens Axboe <axboe@...nel.dk>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 2/6] PM / Runtime: introduce pm_runtime_set[get]_memalloc_noio()

On Wednesday 31 October 2012 00:00:56 Ming Lei wrote:
> On Tue, Oct 30, 2012 at 11:38 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> 
> >
> > Okay, I see your point.  But acquiring the lock here doesn't solve the
> > problem.  Suppose a thread is about to reset a USB mass-storage device.
> > It acquires the lock and sees that the noio flag is clear.  But before
> > it can issue the reset, another thread sets the noio flag.
> 
> If the USB mass-storage device is being reseted, the flag should be set
> already generally.  If the flag is still unset, that means the disk/network
> device isn't added into system(or removed just now), so memory allocation
> with block I/O should be allowed during the reset. Looks it isn't one problem,
> isn't it?

I am afraid it is, because a disk may just have been probed as the deviceis being reset.

	Regards
		Oliver

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