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

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Date:   Mon, 26 Apr 2021 01:29:25 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        lkft-triage@...ts.linaro.org,
        Linux-Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: [PATCH net-next] scm: optimize put_cmsg()

Hi Eric,

On Fri, 16 Apr 2021 at 23:27, Jakub Kicinski <kuba@...nel.org> wrote:
>
> 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.

I have been noticing this problem.

>
> 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.

We (LKFT) are still seeing this problem only on arm architecture on
next-20210416 tag onwards. our bisect script points to this commit.

Steps to reproduce:
- build linux next latest next-20210423 tag with below config
     -  kernel-config:
https://builds.tuxbuild.com/1reqrnNLnHEX9uEZFngRfaoJa9E/config
- boot qemu-arm with below command
   -  /usr/bin/qemu-system-aarch64 -cpu host,aarch64=off -machine
virt-2.10,accel=kvm -nographic -net
nic,model=virtio,macaddr=BA:DD:AD:CC:09:04 -net tap -m 2048 -monitor
none -kernel zImage --append "console=ttyAMA0 root=/dev/vda rw" -hda
rpb-console-image-lkft-am57xx-evm-20201022181203-3085.rootfs.ext4 -m
4096 -smp 2 -nographic

- After the mount rootfs - the systemd gets stuck

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

May I request to investigate this on arm architecture.
The qemu_arm boot failed link,
https://lkft.validation.linaro.org/scheduler/job/2565371#L540

The qemu_arm boot pass after the reverting this patch,
    commit 38ebcf5096a86762b82262e96b2c8b170fe79040
    scm: optimize put_cmsg()

on the latest linux next tags i have to revert two commits.
   "scm: fix a typo in put_cmsg()"
   "scm: optimize put_cmsg()"

Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>

--
Linaro LKFT
https://lkft.linaro.org