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Date:   Fri, 27 Aug 2021 02:39:23 +0000
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From:   yajun.deng@linux.dev
Message-ID: <d6cbd8d362ae84dde2ccde6698be0d3c@linux.dev>
Subject: Re: [PATCH linux-next] PCI: Fix the order in unregister path
To:     "Rob Herring" <robh@kernel.org>
Cc:     "Bjorn Helgaas" <bhelgaas@google.com>,
        "Arnd Bergmann" <arnd@arndb.de>,
        "Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
        "PCI" <linux-pci@vger.kernel.org>, linux-kernel@vger.kernel.org
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References: <CAL_Jsq+rRFJUO3SVLdkQV62dQPymPigiikM05Xipgfbvg_oeqw@mail.gmail.com>
 <20210825083425.32740-1-yajun.deng@linux.dev>
 <CAL_JsqJ4731w_0rYCSBC_Mma-rn4nUUbKnSwhymGZyh8E7xoWg@mail.gmail.com>
 <63e1e9ea1e4b74b56aeafcc6695ecfa8@linux.dev>
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August 26, 2021 8:01 PM, "Rob Herring" <robh@kernel.org> wrote:=0A=0A> On=
 Wed, Aug 25, 2021 at 10:57 PM <yajun.deng@linux.dev> wrote:=0A> =0A>> Au=
gust 25, 2021 9:55 PM, "Rob Herring" <robh@kernel.org> wrote:=0A>> =0A>> =
On Wed, Aug 25, 2021 at 3:34 AM Yajun Deng <yajun.deng@linux.dev> wrote:=
=0A>> =0A>> device_del() should be called first and then called put_devic=
e() in=0A>> unregister path, becase if that the final reference count, th=
e device=0A>> will be cleaned up via device_release() above. So use devic=
e_unregister()=0A>> instead.=0A>> =0A>> Fixes: 9885440b16b8 (PCI: Fix pci=
_host_bridge struct device release/free handling)=0A>> Signed-off-by: Yaj=
un Deng <yajun.deng@linux.dev>=0A>> ---=0A>> drivers/pci/probe.c | 4 +---=
=0A>> 1 file changed, 1 insertion(+), 3 deletions(-)=0A>> =0A>> NAK.=0A>>=
 =0A>> The current code is correct. Go read the comments for device_add/d=
evice_del.=0A>> =0A>> But the device_unregister() is only contains device=
_del() and put_device(). It just put=0A>> device_del() before put_device(=
).=0A> =0A> And that is the wrong order as we want to undo what the code =
above=0A> did. The put_device here is for the get_device we did. The put_=
device=0A> in device_unregister is for the get_device that device_registe=
r did=0A> (on success only).=0A> =0A> Logically, it is wrong too to call =
unregister if register failed. That=0A> would be like doing this:=0A> =0A=
> p =3D malloc(1);=0A> if (!p)=0A> free(p);=0A>=0AThis is the raw code:=
=0A        err =3D device_register(&bus->dev);=0A        if (err)=0A     =
           goto unregister;=0Aunregister:=0A        put_device(&bridge->d=
ev);=0A        device_del(&bridge->dev);=0A=0AThis is my code:=0A        =
err =3D device_register(&bus->dev);=0A        if (err)=0A                =
goto unregister;=0A unregister:=0A        device_unregister(&bridge->dev)=
;=0A=0A=0AThe parameter in  device_register() is bus->dev, but the parame=
ter in device_unregister() is bridge->dev.The are different.=0AThe bridge=
->dev is already success before called device_register().So it wouldn't b=
e happen like your code.=0A=0A =0A> Rob