Re: [PATCH] char: don't fail when client is not connected - Marc-André Lureau

From: "Marc-André Lureau" <marcandre.lureau@redhat.com>
To: Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>,
	"P. Berrange, Daniel" <berrange@redhat.com>
Cc: "Bonzini, Paolo" <pbonzini@redhat.com>,
	qemu-devel <qemu-devel@nongnu.org>
Subject: Re: [PATCH] char: don't fail when client is not connected
Date: Wed, 3 Feb 2021 12:38:19 +0400	[thread overview]
Message-ID: <CAMxuvazS9PCiZM0XNCyLOg9C40XxDytQhsLb1KVrA9NtvU34Bw@mail.gmail.com> (raw)
In-Reply-To: <3f9e991e-da3b-1df5-5124-06dc2e1b7e18@ispras.ru>

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Hi

On Wed, Feb 3, 2021 at 12:22 PM Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>
wrote:

> On 03.02.2021 11:13, Marc-André Lureau wrote:
>
> > Can you provide a reproducer?
>
>
> That was a record/replay scenario. I've used Fedora cloudinit images,
> that are used in acceptance tests:
>
> qemu-system-x86_64 \
>   -display none -vga none -machine pc -smp 1 -m 1024 \
>   -monitor tcp:127.0.0.1:8081,server,nowait \
>   -serial tcp:127.0.0.1:8082,server,nowait \
>   -object filter-replay,id=replay,netdev=hub0port0 \
>   -drive
> file=Fedora-Cloud-Base-31-1.9.x86_64.qcow2,snapshot,id=disk0,if=none \
>   -drive driver=blkreplay,id=disk0-rr,if=none,image=disk0 \
>   -device virtio-blk-pci,drive=disk0-rr,ioeventfd=false \
>   -icount shift=1,rr=record,rrfile=replay.bin \
>   -drive file=cloudinit.iso,snapshot,id=disk1,if=none \
>   -drive driver=blkreplay,id=disk1-rr,if=none,image=disk1 \
>   -device virtio-blk-pci,drive=disk1-rr,ioeventfd=false
>
>
> The failure occurred on replay stage:
>
> qemu-system-x86_64 \
>   -display none -vga none -machine pc -smp 1 -m 1024 \
>   -monitor tcp:127.0.0.1:8081,server,nowait \
>   -serial tcp:127.0.0.1:8082,server,nowait \
>   -object filter-replay,id=replay,netdev=hub0port0 \
>   -drive
> file=Fedora-Cloud-Base-31-1.9.x86_64.qcow2,snapshot,id=disk0,if=none \
>   -drive driver=blkreplay,id=disk0-rr,if=none,image=disk0 \
>   -device virtio-blk-pci,drive=disk0-rr,ioeventfd=false \
>   -icount shift=1,rr=replay,rrfile=replay.bin \
>   -drive file=cloudinit.iso,snapshot,id=disk1,if=none \
>   -drive driver=blkreplay,id=disk1-rr,if=none,image=disk1 \
>   -device virtio-blk-pci,drive=disk1-rr,ioeventfd=false
>

Ah, that helps. qemu_chr_write() will return
replay_char_write_event_load(), bypassing the current state. If the
connected state during replay doesn't match the state during recording, it
is possible to reach the bad condition. (there are probably many such
corner-cases situations with replay..)

Can you update the commit message to explain the relation with replay? with
that:
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Daniel, could you review it too?
thanks

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