On Wed, Feb 10, 2021 at 04:39:06PM -0500, Michael S. Tsirkin wrote: > On Mon, Jan 25, 2021 at 01:01:09PM -0500, Vivek Goyal wrote: > > Hi, > > > > We are working on DAX support in virtiofs and have some patches out of > > the tree hosted here. > > > > https://gitlab.com/virtio-fs/qemu/-/commits/virtio-fs-dev > > > > These patches have not been proposed for merge yet, becasue David > > Gilbert noticed that we can run into a deadlock during an emergency > > reboot of guest kernel. (echo b > /proc/sysrq-trigger). > > > > I have provided details of deadlock in 4th path of the series with > > subject "qemu, vhost-user: Extend protocol to start/stop/flush slave > > channel". > > > > Basic problem seems to be that we don't have a proper mechanism to > > shutdown slave channel when vhost-user device is stopping. This means > > there might be pending messages in slave channel and slave is blocked > > and waiting for response. > > > > This is an RFC patch series to enhance vhost-user protocol to > > properly shutdown/flush slave channel and avoid the deadlock. Though > > we faced the issue in the context of virtiofs, any vhost-user > > device using slave channel can potentially run into issues and > > can benefit from these patches. > > > > Any feedback is welcome. Currently patches are based on out of > > tree code but after I get some feedback, I can only take pieces > > which are relevant to upstream and post separately. > > > > Thanks > > Vivek > > No comments so far - do you plan to post a non-RFC patchset?
Yes. Stefan wants me to poll both unix fd and slave fd in device shutdown path and serve both of these in parallel, instead of adding a new slave channel shutdown message. I am planning to give it a try and post new patches. Vivek > > > > Vivek Goyal (6): > > virtiofsd: Drop ->vu_dispatch_rwlock while waiting for thread to exit > > libvhost-user: Use slave_mutex in all slave messages > > vhost-user: Return error code from slave_read() > > qemu, vhost-user: Extend protocol to start/stop/flush slave channel > > libvhost-user: Add support to start/stop/flush slave channel > > virtiofsd: Opt in for slave start/stop/shutdown functionality > > > > hw/virtio/vhost-user.c | 151 +++++++++++++++++++++- > > subprojects/libvhost-user/libvhost-user.c | 147 +++++++++++++++++---- > > subprojects/libvhost-user/libvhost-user.h | 8 +- > > tools/virtiofsd/fuse_virtio.c | 20 +++ > > 4 files changed, 294 insertions(+), 32 deletions(-) > > > > -- > > 2.25.4 >
