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Date: Wed, 23 Nov 2011 22:19:49 +0100 From: Jiri Slaby <jslaby@...e.cz> To: Havard Skinnemoen <hskinnemoen@...gle.com> CC: Jiri Slaby <jirislaby@...il.com>, Dave Jones <davej@...hat.com>, Linux Kernel <linux-kernel@...r.kernel.org>, Greg Kroah-Hartman <gregkh@...e.de>, Alan Cox <alan@...ux.intel.com> Subject: Re: [RFC] cdc-acm: Fix potential deadlock (lockdep warning) On 11/23/2011 10:11 PM, Jiri Slaby wrote: > On 11/23/2011 10:08 PM, Havard Skinnemoen wrote: >> tty_port_close_start() takes port->lock, so if we try to do that, >> we'll turn a potential deadlock into a real one. Or did you mean >> something else? > > I mean the other uses of port->count in your driver. > >> I think I'll try to follow Alan's advice and use tty_port_close() >> instead of the split functions. > > Yes, that's indeed the best approach. However you have to use them all: > tty_port_open, tty_port_hangup, tty_port_close. OR you would have to do > the locking of count properly. And I see now that the driver uses tty_port_hangup (count under port->lock) and tty_port_close_start (count under open_mutex and port->lock). But doesn't use tty_port_open (count under open_mutex and acm->mutex). Hence there was always a race hangup vs. open wrt. port counting. thanks, -- js suse labs -- 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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