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From: Jason Wang <jasowang@redhat.com>
To: Yongji Xie <xieyongji@bytedance.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, 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: [RFC v3 01/11] eventfd: track eventfd_signal() recursion depth separately in different cases
Date: Thu, 28 Jan 2021 11:04:42 +0800	[thread overview]
Message-ID: <b5c9f2d4-5b95-4552-3886-f5cbcb7de232@redhat.com> (raw)
In-Reply-To: <CACycT3sqDgccOfNcY_FNcHDqJ2DeMbigdFuHYm9DxWWMjkL7CQ@mail.gmail.com>


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).

Thanks


>
> Thanks,
> Yongji
>


  reply	other threads:[~2021-01-28  3:06 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 [this message]
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
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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