From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx123.postini.com [74.125.245.123]) by kanga.kvack.org (Postfix) with SMTP id 760186B006C for ; Tue, 30 Oct 2012 12:54:34 -0400 (EDT) Date: Tue, 30 Oct 2012 12:54:33 -0400 (EDT) From: Alan Stern Subject: Re: [PATCH v3 2/6] PM / Runtime: introduce pm_runtime_set[get]_memalloc_noio() In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Ming Lei Cc: linux-kernel@vger.kernel.org, Oliver Neukum , Minchan Kim , Greg Kroah-Hartman , "Rafael J. Wysocki" , Jens Axboe , "David S. Miller" , Andrew Morton , netdev@vger.kernel.org, linux-usb@vger.kernel.org, linux-pm@vger.kernel.org, linux-mm@kvack.org On Wed, 31 Oct 2012, Ming Lei wrote: > On Tue, Oct 30, 2012 at 11:38 PM, Alan Stern 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? As Oliver said, it can be a problem. > > Lastly, pm_runtime_get_memalloc_noio always returns false when > > CONFIG_PM_RUNTIME is disabled. But we still need to prevent I/O during > > usb_reset_device even when there's no runtime PM. Maybe the simplest > > answer is always to set noio during resets. That would also help with > > the race described above. > > I have thought about this. IMO, pm_runtime_get_memalloc_noio should > return true always if CONFIG_PM_RUNTIME is unset. That's okay as long as the only user of pm_runtime_get_memalloc_noio (apart from the runtime PM core) is usbcore. Alan Stern -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org