netdev - Re: [PATCH net-next] scm: optimize put

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Message-ID: <20210416105735.073466b3@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 16 Apr 2021 10:57:34 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net-next] scm: optimize put_cmsg()

On Thu, 15 Apr 2021 10:37:53 -0700 Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Calling two copy_to_user() for very small regions has very high overhead.
> 
> Switch to inlined unsafe_put_user() to save one stac/clac sequence,
> and avoid copy_to_user().
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Soheil Hassas Yeganeh <soheil@...gle.com>

Hi Eric!

This appears to break boot on my systems.

IDK how exactly, looks like systemd gets stuck waiting for nondescript
services to start in initramfs. I have lots of debug enabled and didn't
spot anything of note in kernel logs.

I'll try to poke at this more, but LMK if you have any ideas. The
commit looks "obviously correct" :S