linux-kernel - Re: [PATCH v2 2/9] driver core: Avoid careless re-use of existing device links

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Message-ID: <20190207190326.wjxnzo4ja62t3mt6@wunner.de>
Date:   Thu, 7 Feb 2019 20:03:26 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Lucas Stach <l.stach@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v2 2/9] driver core: Avoid careless re-use of existing
 device links

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