From: Yongji Xie <xieyongji@bytedance.com>
To: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Stefano Garzarella <sgarzare@redhat.com>,
Parav Pandit <parav@nvidia.com>, Bob Liu <bob.liu@oracle.com>,
Christoph Hellwig <hch@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
viro@zeniv.linux.org.uk, Jens Axboe <axboe@kernel.dk>,
bcrl@kvack.org, Jonathan Corbet <corbet@lwn.net>,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: Re: [RFC v3 01/11] eventfd: track eventfd_signal() recursion depth separately in different cases
Date: Thu, 28 Jan 2021 14:08:58 +0800 [thread overview]
Message-ID: <CACycT3ukfPjnD+o0_xkq9Y9cwDxQUj1dmuuwuVdQvKywjQhRjA@mail.gmail.com> (raw)
In-Reply-To: <9226c594-e045-544d-4e46-c4c3c9c573a9@redhat.com>
On Thu, Jan 28, 2021 at 12:31 PM Jason Wang <jasowang@redhat.com> wrote:
>
>
> On 2021/1/28 上午11:52, Yongji Xie wrote:
> > On Thu, Jan 28, 2021 at 11:05 AM Jason Wang <jasowang@redhat.com> wrote:
> >>
> >> On 2021/1/27 下午5:11, Yongji Xie wrote:
> >>> On Wed, Jan 27, 2021 at 11:38 AM Jason Wang <jasowang@redhat.com> wrote:
> >>>> On 2021/1/20 下午2:52, Yongji Xie wrote:
> >>>>> On Wed, Jan 20, 2021 at 12:24 PM Jason Wang <jasowang@redhat.com> wrote:
> >>>>>> On 2021/1/19 下午12:59, Xie Yongji wrote:
> >>>>>>> Now we have a global percpu counter to limit the recursion depth
> >>>>>>> of eventfd_signal(). This can avoid deadlock or stack overflow.
> >>>>>>> But in stack overflow case, it should be OK to increase the
> >>>>>>> recursion depth if needed. So we add a percpu counter in eventfd_ctx
> >>>>>>> to limit the recursion depth for deadlock case. Then it could be
> >>>>>>> fine to increase the global percpu counter later.
> >>>>>> I wonder whether or not it's worth to introduce percpu for each eventfd.
> >>>>>>
> >>>>>> How about simply check if eventfd_signal_count() is greater than 2?
> >>>>>>
> >>>>> It can't avoid deadlock in this way.
> >>>> I may miss something but the count is to avoid recursive eventfd call.
> >>>> So for VDUSE what we suffers is e.g the interrupt injection path:
> >>>>
> >>>> userspace write IRQFD -> vq->cb() -> another IRQFD.
> >>>>
> >>>> It looks like increasing EVENTFD_WAKEUP_DEPTH should be sufficient?
> >>>>
> >>> Actually I mean the deadlock described in commit f0b493e ("io_uring:
> >>> prevent potential eventfd recursion on poll"). It can break this bug
> >>> fix if we just increase EVENTFD_WAKEUP_DEPTH.
> >>
> >> Ok, so can wait do something similar in that commit? (using async stuffs
> >> like wq).
> >>
> > We can do that. But it will reduce the performance. Because the
> > eventfd recursion will be triggered every time kvm kick eventfd in
> > vhost-vdpa cases:
> >
> > KVM write KICKFD -> ops->kick_vq -> VDUSE write KICKFD
> >
> > Thanks,
> > Yongji
>
>
> Right, I think in the future we need to find a way to let KVM to wakeup
> VDUSE directly.
>
Yes, this would be better.
Thanks,
Yongji
next prev parent reply other threads:[~2021-01-28 6:10 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 4:59 [RFC v3 00/11] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-01-19 4:59 ` [RFC v3 01/11] eventfd: track eventfd_signal() recursion depth separately in different cases Xie Yongji
2021-01-20 4:24 ` Jason Wang
2021-01-20 6:52 ` Yongji Xie
2021-01-27 3:37 ` Jason Wang
2021-01-27 9:11 ` Yongji Xie
2021-01-28 3:04 ` Jason Wang
2021-01-28 3:08 ` Jens Axboe
2021-01-28 5:12 ` Yongji Xie
2021-01-28 3:52 ` Yongji Xie
2021-01-28 4:31 ` Jason Wang
2021-01-28 6:08 ` Yongji Xie [this message]
2021-01-19 4:59 ` [RFC v3 02/11] eventfd: Increase the recursion depth of eventfd_signal() Xie Yongji
2021-01-19 4:59 ` [RFC v3 03/11] vdpa: Remove the restriction that only supports virtio-net devices Xie Yongji
2021-01-20 3:46 ` Jason Wang
2021-01-20 6:46 ` Yongji Xie
2021-01-20 11:08 ` Stefano Garzarella
2021-01-27 3:33 ` Jason Wang
2021-01-27 8:57 ` Stefano Garzarella
2021-01-28 3:11 ` Jason Wang
[not found] ` <20210129150359.caitcskrfhqed73z@steredhat>
2021-01-30 11:33 ` Yongji Xie
2021-02-01 11:05 ` Stefano Garzarella
2021-01-27 8:59 ` Stefano Garzarella
2021-01-27 9:05 ` Yongji Xie
2021-01-19 4:59 ` [RFC v3 04/11] vhost-vdpa: protect concurrent access to vhost device iotlb Xie Yongji
2021-01-20 3:44 ` Jason Wang
2021-01-20 6:44 ` Yongji Xie
2021-01-19 4:59 ` [RFC v3 05/11] vdpa: shared virtual addressing support Xie Yongji
2021-01-20 5:55 ` Jason Wang
2021-01-20 7:10 ` Yongji Xie
2021-01-27 3:43 ` Jason Wang
2021-01-19 4:59 ` [RFC v3 06/11] vhost-vdpa: Add an opaque pointer for vhost IOTLB Xie Yongji
2021-01-20 6:24 ` Jason Wang
2021-01-20 7:52 ` Yongji Xie
2021-01-27 3:51 ` Jason Wang
2021-01-27 9:27 ` Yongji Xie
2021-01-19 5:07 ` [RFC v3 07/11] vdpa: Pass the netlink attributes to ops.dev_add() Xie Yongji
2021-01-19 5:07 ` [RFC v3 08/11] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-01-19 14:53 ` Jonathan Corbet
2021-01-20 2:25 ` Yongji Xie
2021-01-19 17:53 ` Randy Dunlap
2021-01-20 2:42 ` Yongji Xie
2021-01-26 8:08 ` Jason Wang
2021-01-27 8:50 ` Yongji Xie
2021-01-28 4:27 ` Jason Wang
2021-01-28 6:03 ` Yongji Xie
2021-01-28 6:14 ` Jason Wang
2021-01-28 6:43 ` Yongji Xie
2021-01-26 8:19 ` Jason Wang
2021-01-27 8:59 ` Yongji Xie
2021-01-19 5:07 ` [RFC v3 09/11] vduse: Add VDUSE_GET_DEV ioctl Xie Yongji
2021-01-19 5:07 ` [RFC v3 10/11] vduse: grab the module's references until there is no vduse device Xie Yongji
2021-01-26 8:09 ` Jason Wang
2021-01-27 8:51 ` Yongji Xie
2021-01-19 5:07 ` [RFC v3 11/11] vduse: Introduce a workqueue for irq injection Xie Yongji
2021-01-26 8:17 ` Jason Wang
2021-01-27 9:00 ` Yongji Xie
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