linux-kernel - Re: [PATCH RFC] drivers/core: Replace lockdep_set_novalidate

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Message-ID: <Y+memjO1BxrVF20h@moria.home.lan>
Date:   Sun, 12 Feb 2023 21:21:14 -0500
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Kent Overstreet <kent.overstreet@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Coly Li <colyli@...e.de>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        syzkaller <syzkaller@...glegroups.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        Hillf Danton <hdanton@...a.com>
Subject: Re: [PATCH RFC] drivers/core: Replace lockdep_set_novalidate_class()
 with unique class keys

On Sun, Feb 12, 2023 at 08:23:34PM -0500, Alan Stern wrote:
> I really don't think that's a good idea here.  When you've got a bus 
> containing multiple devices, typically all those device structures are 
> created by the same line of code.  So knowing the source code location 
> won't tell you _which_ device structure is involved in the locking 
> cycle or what driver it's using.

Yeah, I was thinking about this more and realized it'd be insufficient.

> By contrast, knowing the device name 
> would.
> 
> Furthermore, to the extent that the device's name identifies what kind 
> of device it is, the name would tell you what where the structure was 
> created and which driver it is using.

OTOH, with the device name, it seems like you'll additionally need the
full device topology to be able to do anything with lockdep splats, no?

What if we just added a way to set a comparison function for a lockdep
class? I'm looking at the lockdep code now, and I think I could do that
for you.