linux-kernel - Re: Possible hungtask issue will be introduced with device_lock() in uevent

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Message-ID: <7b599394-d1a1-4e13-9c5c-48321172ec65@huawei.com>
Date: Sat, 4 Jan 2025 14:02:54 +0800
From: "zhangzekun (A)" <zhangzekun11@...wei.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: <dan.j.williams@...el.com>, <linux-kernel@...r.kernel.org>,
	<rafael.j.wysocki@...el.com>, <regressions@...ts.linux.dev>, <tj@...nel.org>,
	<alex.williamson@...hat.com>, <chenjun102@...wei.com>
Subject: Re: Possible hungtask issue will be introduced with device_lock() in
 uevent_show()

在 2024/12/31 16:26, Greg KH 写道:
> On Tue, Dec 31, 2024 at 03:56:08PM +0800, Zhang Zekun wrote:
>> Hi, Dan, Greg,
>>
>> We have found a potential tungtask issue has been introduce by commit 9a71892cbcdb ("Revert "driver core: Fix uevent_show() vs driver detach race""), which revert the rcu in device_uevent but reintroduce the device_lock() in uevent_show(). The reproduce procedure is quite simple:
> 
> The revert just puts the original logic back in place, so this is not
> anything new that has been introduced, right?  It's just that the
> attempted fix didn't work, so a different fix needs to happen.
Hi, Greg,

Yes, there is nothing new introduced here. We have been testing the rcu 
fix (commit 15fffc6a5624 ("driver core: Fix uevent_show() vs driver 
detach race")) for monthes but has not obersved problems.

Noticing that, brmails+k write in bugzilla "Also, I can't say why the 
issue appeared in the past even without this commit being present, as I 
haven't bisected any kernel version before v6.6.45.". I doubt that there 
could still have problem described in bugzilla [1] even if commit 
c0a40097f0bc ("drivers: core: synchronize really_probe() and 
dev_uevent()") has been reverted, and the problem is not directly 
introduced by rcu in dev_uevent.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=219244

Thanks,
Zekun