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Tsirkin" To: Jason Wang Cc: =?utf-8?B?6buE5p2w?= , Dominique Martinet , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Luis Chamberlain , v9fs-developer@lists.sourceforge.net, Eric Van Hensbergen , Christian Schoenebeck Subject: Re: [External] Re: 9p regression (Was: [PATCH v2] virtio_ring: don't update event idx on get_buf) Message-ID: <20230329012038-mutt-send-email-mst@kernel.org> References: <20230325105633.58592-1-huangjie.albert@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 28, 2023 at 11:39:59AM +0800, Jason Wang wrote: > On Tue, Mar 28, 2023 at 11:09 AM 黄杰 wrote: > > > > Jason Wang 于2023年3月28日周二 10:59写道： > > > > > > On Tue, Mar 28, 2023 at 10:13 AM Dominique Martinet > > > wrote: > > > > > > > > Hi Michael, Albert, > > > > > > > > Albert Huang wrote on Sat, Mar 25, 2023 at 06:56:33PM +0800: > > > > > in virtio_net, if we disable the napi_tx, when we triger a tx interrupt, > > > > > the vq->event_triggered will be set to true. It will no longer be set to > > > > > false. Unless we explicitly call virtqueue_enable_cb_delayed or > > > > > virtqueue_enable_cb_prepare. > > > > > > > > This patch (commited as 35395770f803 ("virtio_ring: don't update event > > > > idx on get_buf") in next-20230327 apparently breaks 9p, as reported by > > > > Luis in https://lkml.kernel.org/r/ZCI+7Wg5OclSlE8c@bombadil.infradead.org > > > > > > > > I've just hit had a look at recent patches[1] and reverted this to test > > > > and I can mount again, so I'm pretty sure this is the culprit, but I > > > > didn't look at the content at all yet so cannot advise further. > > > > It might very well be that we need some extra handling for 9p > > > > specifically that can be added separately if required. > > > > > > > > [1] git log 0ec57cfa721fbd36b4c4c0d9ccc5d78a78f7fa35..HEAD drivers/virtio/ > > > > > > > > > > > > This can be reproduced with a simple mount, run qemu with some -virtfs > > > > argument and `mount -t 9p -o debug=65535 tag mountpoint` will hang after > > > > these messages: > > > > 9pnet: -- p9_virtio_request (83): 9p debug: virtio request > > > > 9pnet: -- p9_virtio_request (83): virtio request kicked > > > > > > > > So I suspect we're just not getting a callback. > > > > > > I think so. The patch assumes the driver will call > > > virtqueue_disable/enable_cb() which is not the case of the 9p driver. > > > > > > So after the first interrupt, event_triggered will be set to true forever. > > > > > > Thanks > > > > > > > Hi: Wang > > > > Yes, This patch assumes that all virtio-related drivers will call > > virtqueue_disable/enable_cb(). > > Thank you for raising this issue. > > > > It seems that napi_tx is only related to virtue_net. I'm thinking if > > we need to refactor > > napi_tx instead of implementing it inside virtio_ring. > > We can hear from others. > > I think it's better not to workaround virtio_ring issues in a specific > driver. It might just add more hacks. We should correctly set > VRING_AVAIL_F_NO_INTERRUPT, I am still stuck trying to understand why we don't set it. How does event_triggered end up getting set without event index support? Thanks!