From: Boris Ostrovsky <boris.ostrovsky@oracle.com> To: Jan Beulich <jbeulich@suse.com>, "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org> Cc: Juergen Gross <jgross@suse.com>, Konrad Wilk <konrad.wilk@oracle.com> Subject: Re: [PATCH 2/3] xen-pciback: reconfigure also from backend watch handler Date: Fri, 9 Apr 2021 17:43:09 -0400 [thread overview] Message-ID: <a93c66e5-807b-e557-d437-48d7f46f25f7@oracle.com> (raw) In-Reply-To: <74955b48-80b1-3436-06b4-d8569260aa65@suse.com> On 4/7/21 10:37 AM, Jan Beulich wrote: > When multiple PCI devices get assigned to a guest right at boot, libxl > incrementally populates the backend tree. The writes for the first of > the devices trigger the backend watch. In turn xen_pcibk_setup_backend() > will set the XenBus state to Initialised, at which point no further > reconfigures would happen unless a device got hotplugged. Arrange for > reconfigure to also get triggered from the backend watch handler. > > Signed-off-by: Jan Beulich <jbeulich@suse.com> > Cc: stable@vger.kernel.org > --- > I will admit that this isn't entirely race-free (with the guest actually > attaching in parallel), but from the looks of it such a race ought to be > benign (not the least thanks to the mutex). Ideally the tool stack > wouldn't write num_devs until all devices had their information > populated. I tried doing so in libxl, but xen_pcibk_setup_backend() > calling xenbus_dev_fatal() when not being able to read that node > prohibits such an approach (or else libxl and driver changes would need > to go into use in lock-step). > > I wonder why what is being watched isn't just the num_devs node. Right > now the watch triggers quite frequently without anything relevant > actually having changed (I suppose in at least some cases in response > to writes by the backend itself). > > --- a/drivers/xen/xen-pciback/xenbus.c > +++ b/drivers/xen/xen-pciback/xenbus.c > @@ -359,7 +359,8 @@ out: > return err; > } > > -static int xen_pcibk_reconfigure(struct xen_pcibk_device *pdev) > +static int xen_pcibk_reconfigure(struct xen_pcibk_device *pdev, > + enum xenbus_state state) > { > int err = 0; > int num_devs; > @@ -374,8 +375,7 @@ static int xen_pcibk_reconfigure(struct > > mutex_lock(&pdev->dev_lock); > /* Make sure we only reconfigure once */ Is this comment still valid or should it be moved ... > - if (xenbus_read_driver_state(pdev->xdev->nodename) != > - XenbusStateReconfiguring) > + if (xenbus_read_driver_state(pdev->xdev->nodename) != state) > goto out; > > err = xenbus_scanf(XBT_NIL, pdev->xdev->nodename, "num_devs", "%d", > @@ -500,6 +500,9 @@ static int xen_pcibk_reconfigure(struct > } > } > > + if (state != XenbusStateReconfiguring) > + goto out; > + ... here? > err = xenbus_switch_state(pdev->xdev, XenbusStateReconfigured); > if (err) { > xenbus_dev_fatal(pdev->xdev, err, > @@ -525,7 +528,7 @@ static void xen_pcibk_frontend_changed(s > break; > > case XenbusStateReconfiguring: > - xen_pcibk_reconfigure(pdev); > + xen_pcibk_reconfigure(pdev, XenbusStateReconfiguring); > break; > > case XenbusStateConnected: > @@ -664,6 +667,10 @@ static void xen_pcibk_be_watch(struct xe > xen_pcibk_setup_backend(pdev); > break; > > + case XenbusStateInitialised: > + xen_pcibk_reconfigure(pdev, XenbusStateInitialised); Could you add a comment here that this is needed when multiple devices are added? It also looks a bit odd that adding a device is now viewed as a reconfiguration. It seems to me that xen_pcibk_setup_backend() and xen_pcibk_reconfigure() really should be merged --- initialization code for both looks pretty much the same. -boris
next prev parent reply other threads:[~2021-04-09 21:43 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-07 14:35 [PATCH 0/3] xen-pciback: a fix, a workaround, and some simplification Jan Beulich 2021-04-07 14:37 ` [PATCH 1/3] xen-pciback: redo VF placement in the virtual topology Jan Beulich 2021-04-08 22:28 ` Boris Ostrovsky 2021-04-09 8:16 ` Jan Beulich 2021-04-07 14:37 ` [PATCH 2/3] xen-pciback: reconfigure also from backend watch handler Jan Beulich 2021-04-09 21:43 ` Boris Ostrovsky [this message] 2021-04-12 9:44 ` Jan Beulich 2021-04-12 15:55 ` Boris Ostrovsky 2021-04-07 14:37 ` [PATCH 3/3] xen-pciback: simplify vpci's find hook Jan Beulich 2021-04-09 21:45 ` Boris Ostrovsky 2021-04-12 9:50 ` Jan Beulich 2021-04-12 16:05 ` Boris Ostrovsky 2021-04-13 8:09 ` Jan Beulich 2021-04-13 12:54 ` Boris Ostrovsky 2021-04-23 8:05 ` Juergen Gross
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