From: Linyu Yuan <quic_linyyuan@quicinc.com>
To: Heikki Krogerus <heikki.krogerus@linux.intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Takashi Iwai <tiwai@suse.de>, <linux-usb@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [REGRESSION 5.19] NULL dereference by ucsi_acpi driver
Date: Tue, 23 Aug 2022 10:26:59 +0800 [thread overview]
Message-ID: <5e17fc89-6056-076c-0c4e-dac7f312792c@quicinc.com> (raw)
In-Reply-To: <YwODjnYQD/KjxXdw@kuha.fi.intel.com>
On 8/22/2022 9:24 PM, Heikki Krogerus wrote:
> Hi,
>
> On Sat, Aug 20, 2022 at 08:40:52PM +0200, Greg Kroah-Hartman wrote:
>> On Fri, Aug 19, 2022 at 06:32:43PM +0200, Takashi Iwai wrote:
>>> Hi,
>>>
>>> we've got multiple reports about 5.19 kernel starting crashing after
>>> some time, and this turned out to be triggered by ucsi_acpi driver.
>>> The details are found in:
>>> https://bugzilla.suse.com/show_bug.cgi?id=1202386
>>>
>>> The culprit seems to be the commit 87d0e2f41b8c
>>> usb: typec: ucsi: add a common function ucsi_unregister_connectors()
>> Adding Heikki to the thread...
>>
>>>
>>> This commit looks as if it were a harmless cleanup, but this failed in
>>> a subtle way. Namely, in the error scenario, the driver gets an error
>>> at ucsi_register_altmodes(), and goes to the error handling to release
>>> the resources. Through this refactoring, the release part was unified
>>> to a funciton ucsi_unregister_connectors(). And there, it has a NULL
>>> check of con->wq, and it bails out the loop if it's NULL.
>>> Meanwhile, ucsi_register_port() itself still calls destroy_workqueue()
>>> and clear con->wq at its error path. This ended up in the leftover
>>> power supply device with the uninitialized / cleared device.
>>>
>>> It was confirmed that the problem could be avoided by a simple
>>> revert.
>> I'll be glad to revert this now, unless Heikki thinks:
>>
>>> I guess another fix could be removing the part clearing con->wq, i.e.
>>>
>>> --- a/drivers/usb/typec/ucsi/ucsi.c
>>> +++ b/drivers/usb/typec/ucsi/ucsi.c
>>> @@ -1192,11 +1192,6 @@ static int ucsi_register_port(struct ucsi *ucsi, int index)
>>> out_unlock:
>>> mutex_unlock(&con->lock);
>>>
>>> - if (ret && con->wq) {
>>> - destroy_workqueue(con->wq);
>>> - con->wq = NULL;
>>> - }
>>> -
>>> return ret;
>>> }
>>>
>>>
>>> ... but it's totally untested and I'm not entirely sure whether it's
>>> better.
>> that is any better?
> No, I don't think that's better. Right now I would prefer that we play
> it safe and revert.
>
> The conditions are different in the two places where the ports are
> unregistered in this driver. Therefore I don't think it makes sense
> to use a function like ucsi_unregister_connectors() that tries to
> cover both cases. It will always be a little bit fragile.
>
> Instead we could introduce a function that can be used to remove a
> single port. That would leave the handling of the conditions to the
> callers of the function, but it would still remove the boilerplate.
> That would be much safer IMO.
>
> But to fix this problem, I think we should revert.
but revert will happen on several stable branch, right ?
i think simple fix is good, from my view there is no big differences to
create a function for a single port.
>
> thanks,
>
next prev parent reply other threads:[~2022-08-23 2:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-19 16:32 [REGRESSION 5.19] NULL dereference by ucsi_acpi driver Takashi Iwai
2022-08-20 18:40 ` Greg Kroah-Hartman
2022-08-22 2:44 ` Linyu Yuan
2022-08-30 12:51 ` Greg Kroah-Hartman
2022-08-30 12:53 ` Greg Kroah-Hartman
2022-08-22 13:24 ` Heikki Krogerus
2022-08-23 2:26 ` Linyu Yuan [this message]
2022-08-23 6:41 ` Greg Kroah-Hartman
2022-08-23 6:52 ` Takashi Iwai
2022-08-24 9:50 ` Thorsten Leemhuis
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