linux-kernel - Re: [PATCH v2 ] devcoredump : Serialize devcd

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Message-ID: <8186de033c87f0cdec296ae272a72c5b9a2880a3.camel@sipsolutions.net>
Date:   Mon, 25 Apr 2022 19:19:58 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Mukesh Ojha <quic_mojha@...cinc.com>,
        linux-kernel@...r.kernel.org
Cc:     sboyd@...nel.org, rafael@...nel.org, gregkh@...uxfoundation.org
Subject: Re: [PATCH v2 ] devcoredump : Serialize devcd_del work

On Mon, 2022-04-25 at 19:00 +0200, Thomas Gleixner wrote:
> 
> Johannes, can you please explain whether this immediate flush in
> disabled_store() is really required and if so, why?
> 

I don't really know, as I remember that requirement (or maybe even code,
not sure) came from Kees, who needed the lockdown.

Given the use case (ChromeOS?) I'm not sure I see a need to flush all of
them, since I guess a typical system would set the lockdown early in
boot and hopefully not have a crash-dump around already.

That said, I don't think the diagram you made works - fn() during the
iteration is guaranteed to be invoked with a reference of its own, so
the put_device() there can't be the last reference, only as fn() returns
you'd put the last reference *there*, freeing it.

johannes