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Message-ID: <Pine.LNX.4.44L0.1205241029260.1349-100000@iolanthe.rowland.org> Date: Thu, 24 May 2012 10:37:40 -0400 (EDT) From: Alan Stern <stern@...land.harvard.edu> To: Greg KH <gregkh@...uxfoundation.org> cc: Ming Lei <ming.lei@...onical.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>, Linux PM List <linux-pm@...r.kernel.org> Subject: Re: Race condition between driver_probe_device and device_shutdown On Wed, 23 May 2012, Greg KH wrote: > On Thu, May 24, 2012 at 09:39:46AM +0800, Ming Lei wrote: > > On Wed, May 23, 2012 at 11:06 PM, Alan Stern <stern@...land.harvard.edu> wrote: > > > On Wed, 23 May 2012, Ming Lei wrote: > > >> The .shutdown callback pointer is got from device->driver, which is > > >> changed in probe and release path. Also runtime PM thing has been > > >> involved into shutting down recently, so looks not only hardware parts > > >> are involved now. > > > > > > This is a tricky question. Overall I think you're probably right. > > > > > > It's certainly true that holding the device lock across the shutdown > > > callback is the easiest and most reliable way to prevent these races. > > > > But holding device lock across .shutdown is very inefficient because > > most of devices' driver have not shutdown callback, so I think it is better The code there is racy already. It does: } else if (dev->driver && dev->driver->shutdown) { without any locking protection. If the driver is unbound while this statement runs then dev->driver could be non-NULL for the first test and NULL for the second. > > to fix the race by prevent driver core from probing or releasing once > > shutdown is started. > > > > How about the below patch? > > How about waiting for the original poster to respond as to exactly how > they are hitting this race before doing anything? In addition, the patch is too complicated. For this type of synchronization you should use SRCU. See Documentation/RCU/whatisRCU.txt and related files. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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