linux-kernel - Re: [RFC] Are you good with Lockdep?

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Message-ID: <20201116084527.GA26078@X58A-UD3R>
Date:   Mon, 16 Nov 2020 17:45:27 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        Sasha Levin <alexander.levin@...rosoft.com>,
        "Wilson, Chris" <chris@...is-wilson.co.uk>, duyuyang@...il.com,
        Johannes Berg <johannes.berg@...el.com>,
        Tejun Heo <tj@...nel.org>, Theodore Ts'o <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        Amir Goldstein <amir73il@...il.com>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Greg KH <gregkh@...uxfoundation.org>, kernel-team@....com
Subject: Re: [RFC] Are you good with Lockdep?

On Thu, Nov 12, 2020 at 02:56:49PM +0100, Daniel Vetter wrote:
> > > I think I understand it. For things like completions and other "wait for
> > > events" we have lockdep annotation, but it is rather awkward to implement.
> > > Having something that says "lockdep_wait_event()" and
> > > "lockdep_exec_event()" wrappers would be useful.
> >
> > Yes. It's a problem of lack of APIs. It can be done by reverting revert
> > of cross-release without big change. ;-)
> 
> +1 on lockdep-native support for this. For another use case I've added
> annotations for dma_fence_wait, and they're not entirely correct
> unfortunately. But the false positives is along the lines of "you

I'd like to help you solve the problem you are facing. Let me be back
and help you later. I have to all-stop what I'm doing at the moment
becasue of a very big personal issue, which is a sad thing.

Thank you,
Byungchul

> really shouldn't do this, even if it's in theory deadlock free". See
> 
> commit 5fbff813a4a328b730cb117027c43a4ae9d8b6c0
> Author: Daniel Vetter <daniel.vetter@...ll.ch>
> Date:   Tue Jul 7 22:12:05 2020 +0200
> 
>    dma-fence: basic lockdep annotations
> 
> for fairly lengthy discussion of the problem and what I ended up with.
> 
> Thanks, Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch