netdev - Re: [PATCH] virtio_net: Revert "virtio_net: set the default max ring size by find

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Message-ID: <20220815203426.GA509309@roeck-us.net>
Date:   Mon, 15 Aug 2022 13:34:26 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Jason Wang <jasowang@...hat.com>,
        Andres Freund <andres@...razel.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Greg KH <gregkh@...uxfoundation.org>, c@...hat.com
Subject: Re: [PATCH] virtio_net: Revert "virtio_net: set the default max ring
 size by find_vqs()"

On Mon, Aug 15, 2022 at 05:16:50AM -0400, Michael S. Tsirkin wrote:
> This reverts commit 762faee5a2678559d3dc09d95f8f2c54cd0466a7.
> 
> This has been reported to trip up guests on GCP (Google Cloud).  Why is
> not yet clear - to be debugged, but the patch itself has several other
> issues:
> 
> - It treats unknown speed as < 10G
> - It leaves userspace no way to find out the ring size set by hypervisor
> - It tests speed when link is down
> - It ignores the virtio spec advice:
>         Both \field{speed} and \field{duplex} can change, thus the driver
>         is expected to re-read these values after receiving a
>         configuration change notification.
> - It is not clear the performance impact has been tested properly
> 
> Revert the patch for now.
> 
> Link: https://lore.kernel.org/r/20220814212610.GA3690074%40roeck-us.net
> Link: https://lore.kernel.org/r/20220815070203.plwjx7b3cyugpdt7%40awork3.anarazel.de
> Link: https://lore.kernel.org/r/3df6bb82-1951-455d-a768-e9e1513eb667%40www.fastmail.com
> Link: https://lore.kernel.org/r/FCDC5DDE-3CDD-4B8A-916F-CA7D87B547CE%40anarazel.de
> Fixes: 762faee5a267 ("virtio_net: set the default max ring size by find_vqs()")
> Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> Cc: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> Tested-by: Andres Freund <andres@...razel.de>

I ran this patch through a total of 14 syskaller tests, 2 test runs each on
7 different crashes reported by syzkaller (as reported to the linux-kernel
mailing list). No problems were reported. I also ran a single cross-check
with one of the syzkaller runs on top of v6.0-rc1, without this patch.
That test run failed.

Overall, I think we can call this fixed.

Guenter

---
syskaller reports:

Reported-and-tested-by: syzbot+2984d1b7aef6b51353f0@...kaller.appspotmail.com

Tested on:

commit:         568035b0 Linux 6.0-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.0-rc1
kernel config:  https://syzkaller.appspot.com/x/.config?x=3b9175e0879a7749
dashboard link: https://syzkaller.appspot.com/bug?extid=2984d1b7aef6b51353f0
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: i386
patch:          https://syzkaller.appspot.com/x/patch.diff?x=11949fc3080000

Reported-and-tested-by: syzbot+2c35c4d66094ddfe198e@...kaller.appspotmail.com

Tested on:

commit:         568035b0 Linux 6.0-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.0-rc1
kernel config:  https://syzkaller.appspot.com/x/.config?x=3cb39b084894e9a5
dashboard link: https://syzkaller.appspot.com/bug?extid=2c35c4d66094ddfe198e
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=163e20f3080000

Reported-and-tested-by: syzbot+97f830ad641de86d08c0@...kaller.appspotmail.com

Tested on:

commit:         568035b0 Linux 6.0-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.0-rc1
kernel config:  https://syzkaller.appspot.com/x/.config?x=f267ed4fb258122a
dashboard link: https://syzkaller.appspot.com/bug?extid=97f830ad641de86d08c0
compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=146c8e5b080000

Reported-and-tested-by: syzbot+005efde5e97744047fe4@...kaller.appspotmail.com

Tested on:

commit:         568035b0 Linux 6.0-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.0-rc1
kernel config:  https://syzkaller.appspot.com/x/.config?x=3cb39b084894e9a5
dashboard link: https://syzkaller.appspot.com/bug?extid=005efde5e97744047fe4
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=106c8e5b080000

Reported-and-tested-by: syzbot+9ada839c852179f13999@...kaller.appspotmail.com

Tested on:

commit:         568035b0 Linux 6.0-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.0-rc1
kernel config:  https://syzkaller.appspot.com/x/.config?x=3b9175e0879a7749
dashboard link: https://syzkaller.appspot.com/bug?extid=9ada839c852179f13999
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=118756f3080000

Reported-and-tested-by: syzbot+382af021ce115a936b1f@...kaller.appspotmail.com

Tested on:

commit:         568035b0 Linux 6.0-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.0-rc1
kernel config:  https://syzkaller.appspot.com/x/.config?x=e656d8727a25e83b
dashboard link: https://syzkaller.appspot.com/bug?extid=382af021ce115a936b1f
compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=135f650d080000

Reported-and-tested-by: syzbot+24df94a8d05d5a3e68f0@...kaller.appspotmail.com

Tested on:

commit:         568035b0 Linux 6.0-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.0-rc1
kernel config:  https://syzkaller.appspot.com/x/.config?x=3b9175e0879a7749
dashboard link: https://syzkaller.appspot.com/bug?extid=24df94a8d05d5a3e68f0
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12758a47080000