From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lukas Wunner <lukas@wunner.de>
Subject: Re: [PATCH v2 2/9] driver core: Avoid careless re-use of existing
 device links
Date: Thu, 7 Feb 2019 20:03:26 +0100
Message-ID: <20190207190326.wjxnzo4ja62t3mt6@wunner.de>
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To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, LKML <linux-kernel@vger.kernel.org>, Linux PM <linux-pm@vger.kernel.org>, Ulf Hansson <ulf.hansson@linaro.org>, Daniel Vetter <daniel@ffwll.ch>, Andrzej Hajda <a.hajda@samsung.com>, Russell King - ARM Linux <linux@armlinux.org.uk>, Lucas Stach <l.stach@pengutronix.de>, Linus Walleij <linus.walleij@linaro.org>, Thierry Reding <thierry.reding@gmail.com>, Laurent Pinchart <laurent.pinchart@ideasonboard.com>, Marek Szyprowski <m.szyprowski@samsung.com>, Joerg Roedel <jroedel@suse.de>
List-Id: linux-pm@vger.kernel.org

Sorry, late to the party.

On Fri, Feb 01, 2019 at 01:46:54AM +0100, Rafael J. Wysocki wrote:
> After commit ead18c23c263 ("driver core: Introduce device links
> reference counting"), if there is a link between the given supplier
> and the given consumer already, device_link_add() will refcount it
> and return it unconditionally.  However, if the flags passed to
> it on the second (or any subsequent) attempt to create a device
> link between the same consumer-supplier pair are not compatible with
> the existing link's flags, that is incorrect.

Prior to ead18c23c263, a second invocation of device_link_add() also
returned the existing device link without checking for incompatible
flags.  Hence this issue was not introduced by ead18c23c263, but
rather by 9ed9895370ae ("driver core: Functional dependencies tracking
support"), i.e. it was present all along.  (Unless I'm missing something.)


> Moreover, if the DL_FLAG_AUTOREMOVE_CONSUMER flag is passed to
> device_link_add(), its caller will expect its reference to the link
> to be dropped automatically on consumer driver removal, which will
> not happen if that flag is not set in the link's flags (and
> analogously for DL_FLAG_AUTOREMOVE_SUPPLIER).  For this reason, make
> device_link_add() update the existing link's flags accordingly
> before returning it to the caller.

Same here.


> Fixes: ead18c23c263 ("driver core: Introduce device links reference counting")

Should rather be
Fixes: 9ed9895370ae ("driver core: Functional dependencies tracking support")

(Again, unless I'm missing something.)

Thanks,

Lukas