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Date: Tue, 7 Nov 2023 11:08:59 +0000
From: Will Deacon <will@kernel.org>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: Eduardo Bart <edub4rt@gmail.com>, kvm@vger.kernel.org,
	alex@mikhalevich.com
Subject: Re: [PATCH kvmtool] virtio: Cancel and join threads when exiting
 devices
Message-ID: <20231107110858.GA19219@willie-the-truck>
References: <CABqCASLWAZ5aq27GuQftWsXSf7yLFCKwrJxWMUF-fiV7Bc4LUA@mail.gmail.com>
 <20231016115259.GA835650@myrica>
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User-Agent: Mutt/1.10.1 (2018-07-13)

On Mon, Oct 16, 2023 at 12:52:59PM +0100, Jean-Philippe Brucker wrote:
> On Wed, Oct 04, 2023 at 05:49:45PM -0300, Eduardo Bart wrote:
> > I'm experiencing a segmentation fault in lkvm where it may crash after
> > powering off a guest machine that uses a virtio network device.
> > The crash is hard to reproduce, because looks like it only happens
> > when the guest machine is powering off while extra virtio threads is
> > doing some work,
> > when it happens lkvm crashes in the function virtio_net_rx_thread
> > while attempting to read invalid guest physical memory,
> > because guest physical memory was unmapped.
> > 
> > I've isolated the problem and looks like when lkvm exits it unmaps the
> > guest memory while virtio device extra threads may still be executing.
> > I noticed most virtio devices are not executing pthread_cancel +
> > pthread_join to synchronize extra threads when exiting,
> > to make sure this happens I added explicit calls to the virtio device
> > exit function to all virtio devices,
> > which should cancel and join all threads before unmapping guest
> > physical memory, fixing the crash for me.
> > 
> > Below I'm attaching a patch to fix the issue, feel free to apply or
> > fix the issue some other way.
> > 
> > Signed-off-by: Eduardo Bart <edub4rt@gmail.com>
> 
> The patch doesn't apply for some reason, there seems to be whitespace
> issues, tabs replaced by spaces.

Eduardo -- please can you send a properly formatted patch addressing
Jean-Philippe's comments so that I can apply it?

Thanks,

Will