On Fri, Aug 24, 2018 at 10:32:58AM +0200, Marc-André Lureau wrote: > Hi > > On Fri, Aug 24, 2018 at 5:45 AM, Peter Xu <pet...@redhat.com> wrote: > > On Thu, Aug 23, 2018 at 04:31:20PM +0200, Marc-André Lureau wrote: > >> Hi, > >> > >> In commit 25679e5d58e "chardev: tcp: postpone async connection setup" > >> (and its follow up 99f2f54174a59), Peter moved chardev socket > >> connection to machine_done event. However, chardev created later will > >> no longer attempt to connect, and chardev created in tests do not have > >> machine_done event (breaking some of vhost-user-test). > >> > >> The goal was to move the "connect" source to the chardev frontend > >> context (the monitor thread context in his case). chr->gcontext is set > >> with qemu_chr_fe_set_handlers(). But there is no guarantee that the > >> function will be called in general, so we can't delay connection until > >> then: the chardev should still attempt to connect during open(), using > >> the main context. > >> > >> An alternative would be to specify the iothread during chardev > >> creation. Setting up monitor OOB would be quite different too, it > >> would take the same iothread as argument. > >> > >> 99f2f54174a595e is also a bit problematic, since it will behave > >> differently before and after machine_done (the first case gives a > >> chance to use a different context reliably, the second looks racy) > >> > >> In the end, I am not sure this is all necessary, as chardev callbacks > >> are called after qemu_chr_fe_set_handlers(), at which point the > >> context of sources are updated. In "char-socket: update all ioc > >> handlers when changing context", I moved also the hup handler to the > >> updated context. So unless the main thread is already stuck, we can > >> setup a different context for the chardev at that time. Or not? > >> > >> v2: > >> - fix a random socket chardev test failure > > > > I have no problem on patch 3-5, but aren't patch 1-2 still breaking > > the context switch of chardev? Or did I misunderstood? > > Switching context is broken/racy regardless. My current plan is to > suspend the context to switch to, and update all sources before > thawing the target context. > > If you prefer we can delay the revert, but I would rather have them > because the regression seems much worse to me.
Have you started working on above? I started to code up some RFC patch to let the chardev maintain the iothreads (now it'll only have a monitor iothread) then we don't need to switch context for chardev any more. I plan to post it today for a quick look. With that, this series will not break anything then. > > > > > Regards, > > > > -- > > Peter Xu Regards, -- Peter Xu
