On 06.02.26 17:57, Marek Marczykowski-Górecki wrote:
On Thu, Jan 29, 2026 at 08:02:35AM +0100, Jürgen Groß wrote:On 26.01.26 08:08, Jürgen Groß wrote:On 17.11.25 12:06, Jürgen Groß wrote:On 02.11.25 04:20, Marek Marczykowski-Górecki wrote:When the backend domain crashes, coordinated device cleanup is not possible (as it involves waiting for the backend state change). In that case, toolstack forcefully removes frontend xenstore entries. xenbus_dev_changed() handles this case, and triggers device cleanup. It's possible that toolstack manages to connect new device in that place, before xenbus_dev_changed() notices the old one is missing. If that happens, new one won't be probed and will forever remain in XenbusStateInitialising.Fix this by checking backend-id and if it changes, consider it unplug+plug operation. It's important that cleanup on such unplug doesn't modify xenstore entries (especially the "state" key) as it belong to the new device to be probed - changing it would derail establishing connection to the new backend (most likely, closing the device before it was even connected). Handle this case by setting new xenbus_device->vanished flag to true, and check it before changing state entry. And even if xenbus_dev_changed() correctly detects the device was forcefully removed, the cleanup handling is still racy. Since this whole handling doesn't happend in a single xenstore transaction, it's possible that toolstack might put a new device there already. Avoid re-creating the state key (which in the case of loosing the race would actually close newly attached device). The problem does not apply to frontend domain crash, as this case involves coordinated cleanup. Problem originally reported at https://lore.kernel.org/xen-devel/aOZvivyZ9YhVWDLN@mail-itl/T/#t, including reproduction steps. Signed-off-by: Marek Marczykowski-Górecki <[email protected]>Sorry I didn't get earlier to this. My main problem with this patch is that it is basically just papering over a more general problem. You are just making the problem much more improbable, but not impossible to occur again. In case the new driver domain has the same domid as the old one you can still have the same race. The clean way to handle that would be to add a unique Id in Xenstore to each device on the backend side, which can be tested on the frontend side to match. In case it doesn't match, an old device with the same kind and devid can be cleaned up. The unique Id would obviously need to be set by the Xen tools inside the transaction writing the initial backend Xenstore nodes, as doing that from the backend would add another potential ambiguity by the driver domain choosing the same unique id as the previous one did. The question is whether something like your patch should be used as a fallback in case there is no unique Id on the backend side of the device due to a too old Xen version.I think I have found a solution which is much more simple, as it doesn't need any change of the protocol or any addition of new identifiers. When creating a new PV device, Xen tools will always write all generic frontend- and backend-nodes. This includes the frontend state, which is initialized as XenbusStateInitialising. The Linux kernel's xenbus driver is already storing the last known state of a xenbus device in struct xenbus_device. When changing the state, the xenbus driver is even reading the state from Xenstore (even if only for making sure the path is still existing). So all what is needed is to check, whether the read current state is matching the locally saved state. If it is not matching AND the read state is XenbusStateInitialising, you can be sure that the backend has been replaced. Handling this will need to check the return value of xenbus_switch_state() in all related drivers, but this is just a more or less mechanical change. I'll prepare a patch series for that.In the end the result is more like your patch, avoiding the need to modify all drivers. I just added my idea to your patch and modified some of your code to be more simple. I _think_ I have covered all possible scenarios now, resulting in the need to keep the backend id check in case the backend died during the early init phase of the device. Could you please verify the attached patch is working for you?Thanks for the patch! I ran it through relevant tests, and I got inconsistent results. Specifically, sometimes, the domU hangs (actually, just one vCPU spins inside xenwatch thread). Last console messages are: systemd[626]: Starting dconf.service - User preferences database... gnome-keyring-daemon[975]: ␛[0;1;39mcouldn't access control socket: /run/user/1000/keyring/control: No such file or directory␛[0m gnome-keyring-daemon[975]: ␛[0;1;38:5:185mdiscover_other_daemon: 0␛[0m xen vif-0: xenbus: state reset occurred, reconnecting gnome-keyring-daemon[974]: ␛[0;1;39mcouldn't access control socket: /run/user/1000/keyring/control: No such file or directory␛[0m gnome-keyring-daemon[976]: ␛[0;1;39mcouldn't access control socket: /run/user/1000/keyring/control: No such file or directory␛[0m gnome-keyring-daemon[976]: ␛[0;1;38:5:185mdiscover_other_daemon: 0␛[0m gnome-keyring-daemon[974]: ␛[0;1;38:5:185mdiscover_other_daemon: 0␛[0m xen vif-0: xenbus: state reset occurred, reconnecting systemd[626]: Started dconf.service - User preferences database. xen_netfront: Initialising Xen virtual ethernet driver vif vif-0: xenbus: state reset occurred, reconnecting And the call trace of the spinning xenwatch thread is: task:xenwatch state:D stack:0 pid:64 tgid:64 ppid:2 task_flags:0x288040 flags:0x00080000 Call Trace: <TASK> __schedule+0x2f3/0x780 schedule+0x27/0x80 xs_wait_for_reply+0xab/0x1f0 ? __pfx_autoremove_wake_function+0x10/0x10 xs_talkv+0xec/0x200 xs_single+0x4a/0x70 xenbus_gather+0xe4/0x1a0 xenbus_read_driver_state+0x42/0x70 xennet_bus_close+0x113/0x2c0 [xen_netfront] ? __pfx_autoremove_wake_function+0x10/0x10 xennet_remove+0x16/0x80 [xen_netfront] xenbus_dev_remove+0x71/0xf0 device_release_driver_internal+0x19c/0x200 bus_remove_device+0xc6/0x130 device_del+0x160/0x3e0 device_unregister+0x17/0x60 xenbus_dev_changed.cold+0x5e/0x6b ? __pfx_xenwatch_thread+0x10/0x10 xenwatch_thread+0x92/0x1c0 ? __pfx_autoremove_wake_function+0x10/0x10 kthread+0xfc/0x240 ? __pfx_kthread+0x10/0x10 ret_from_fork+0xf5/0x110 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> task:xenbus state:S stack:0 pid:63 tgid:63 ppid:2 task_flags:0x208040 flags:0x00080000 Call Trace: <TASK> __schedule+0x2f3/0x780 ? __pfx_xenbus_thread+0x10/0x10 schedule+0x27/0x80 xenbus_thread+0x1a8/0x200 ? __pfx_autoremove_wake_function+0x10/0x10 kthread+0xfc/0x240 ? __pfx_kthread+0x10/0x10 ret_from_fork+0xf5/0x110 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> (technically, `top` says it's the xenbus thread spinning, but it looks like the actual issue is in xenwatch one) Note that other xenwatch actions in this domU are not executed, for example `xl sysrq` does nothing. Not surprising, given xenwatch thread is busy... Fortunately, it blocks only a single vCPU, so I'm able to interact with the domU over console (to get the above traces). It isn't a reliable failure, in this test run it failed once, out of 4 related tests. The specific test is: https://github.com/QubesOS/qubes-core-admin/blob/main/qubes/tests/integ/network.py#L234 In short: 1. Start a domU 2. Pause it 3. Attach network (backend is != dom0) 4. Unpause TBH, I'm not sure why the "state reset occurred" message is triggered at all, I think it shouldn't be in this case...
Second try. Juergen
From be50f0a4041116392864a9acb37315c8b8c076a7 Mon Sep 17 00:00:00 2001 From: Juergen Gross <[email protected]> Date: Mon, 9 Feb 2026 08:42:06 +0100 Subject: [PATCH 1/2] xenbus: add xenbus_device parameter to xenbus_read_driver_state() In order to prepare checking the xenbus device status in xenbus_read_driver_state(), add the pointer to struct xenbus_device as a parameter. Signed-off-by: Juergen Gross <[email protected]> --- drivers/net/xen-netfront.c | 34 +++++++++++----------- drivers/pci/xen-pcifront.c | 8 ++--- drivers/scsi/xen-scsifront.c | 2 +- drivers/xen/xen-pciback/xenbus.c | 10 +++---- drivers/xen/xenbus/xenbus_client.c | 3 +- drivers/xen/xenbus/xenbus_probe.c | 6 ++-- drivers/xen/xenbus/xenbus_probe_frontend.c | 2 +- include/xen/xenbus.h | 3 +- 8 files changed, 35 insertions(+), 33 deletions(-) diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c index 7c2220366623..e2da977c9c50 100644 --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -1646,7 +1646,7 @@ static int xennet_xdp_set(struct net_device *dev, struct bpf_prog *prog, /* avoid the race with XDP headroom adjustment */ wait_event(module_wq, - xenbus_read_driver_state(np->xbdev->otherend) == + xenbus_read_driver_state(np->xbdev, np->xbdev->otherend) == XenbusStateReconfigured); np->netfront_xdp_enabled = true; @@ -1764,9 +1764,9 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev) do { xenbus_switch_state(dev, XenbusStateInitialising); err = wait_event_timeout(module_wq, - xenbus_read_driver_state(dev->otherend) != + xenbus_read_driver_state(dev, dev->otherend) != XenbusStateClosed && - xenbus_read_driver_state(dev->otherend) != + xenbus_read_driver_state(dev, dev->otherend) != XenbusStateUnknown, XENNET_TIMEOUT); } while (!err); @@ -2627,31 +2627,31 @@ static void xennet_bus_close(struct xenbus_device *dev) { int ret; - if (xenbus_read_driver_state(dev->otherend) == XenbusStateClosed) + if (xenbus_read_driver_state(dev, dev->otherend) == XenbusStateClosed) return; do { xenbus_switch_state(dev, XenbusStateClosing); ret = wait_event_timeout(module_wq, - xenbus_read_driver_state(dev->otherend) == - XenbusStateClosing || - xenbus_read_driver_state(dev->otherend) == - XenbusStateClosed || - xenbus_read_driver_state(dev->otherend) == - XenbusStateUnknown, - XENNET_TIMEOUT); + xenbus_read_driver_state(dev, dev->otherend) == + XenbusStateClosing || + xenbus_read_driver_state(dev, dev->otherend) == + XenbusStateClosed || + xenbus_read_driver_state(dev, dev->otherend) == + XenbusStateUnknown, + XENNET_TIMEOUT); } while (!ret); - if (xenbus_read_driver_state(dev->otherend) == XenbusStateClosed) + if (xenbus_read_driver_state(dev, dev->otherend) == XenbusStateClosed) return; do { xenbus_switch_state(dev, XenbusStateClosed); ret = wait_event_timeout(module_wq, - xenbus_read_driver_state(dev->otherend) == - XenbusStateClosed || - xenbus_read_driver_state(dev->otherend) == - XenbusStateUnknown, - XENNET_TIMEOUT); + xenbus_read_driver_state(dev, dev->otherend) == + XenbusStateClosed || + xenbus_read_driver_state(dev, dev->otherend) == + XenbusStateUnknown, + XENNET_TIMEOUT); } while (!ret); } diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c index 11636634ae51..cd22bf984024 100644 --- a/drivers/pci/xen-pcifront.c +++ b/drivers/pci/xen-pcifront.c @@ -856,7 +856,7 @@ static void pcifront_try_connect(struct pcifront_device *pdev) int err; /* Only connect once */ - if (xenbus_read_driver_state(pdev->xdev->nodename) != + if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename) != XenbusStateInitialised) return; @@ -876,7 +876,7 @@ static int pcifront_try_disconnect(struct pcifront_device *pdev) enum xenbus_state prev_state; - prev_state = xenbus_read_driver_state(pdev->xdev->nodename); + prev_state = xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename); if (prev_state >= XenbusStateClosing) goto out; @@ -895,7 +895,7 @@ static int pcifront_try_disconnect(struct pcifront_device *pdev) static void pcifront_attach_devices(struct pcifront_device *pdev) { - if (xenbus_read_driver_state(pdev->xdev->nodename) == + if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename) == XenbusStateReconfiguring) pcifront_connect(pdev); } @@ -909,7 +909,7 @@ static int pcifront_detach_devices(struct pcifront_device *pdev) struct pci_dev *pci_dev; char str[64]; - state = xenbus_read_driver_state(pdev->xdev->nodename); + state = xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename); if (state == XenbusStateInitialised) { dev_dbg(&pdev->xdev->dev, "Handle skipped connect.\n"); /* We missed Connected and need to initialize. */ diff --git a/drivers/scsi/xen-scsifront.c b/drivers/scsi/xen-scsifront.c index 924025305753..ef74d4da5ab0 100644 --- a/drivers/scsi/xen-scsifront.c +++ b/drivers/scsi/xen-scsifront.c @@ -1175,7 +1175,7 @@ static void scsifront_backend_changed(struct xenbus_device *dev, return; } - if (xenbus_read_driver_state(dev->nodename) == + if (xenbus_read_driver_state(dev, dev->nodename) == XenbusStateInitialised) scsifront_do_lun_hotplug(info, VSCSIFRONT_OP_ADD_LUN); diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c index b11e401f1b1e..4bd1c7a8957e 100644 --- a/drivers/xen/xen-pciback/xenbus.c +++ b/drivers/xen/xen-pciback/xenbus.c @@ -149,12 +149,12 @@ static int xen_pcibk_attach(struct xen_pcibk_device *pdev) mutex_lock(&pdev->dev_lock); /* Make sure we only do this setup once */ - if (xenbus_read_driver_state(pdev->xdev->nodename) != + if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename) != XenbusStateInitialised) goto out; /* Wait for frontend to state that it has published the configuration */ - if (xenbus_read_driver_state(pdev->xdev->otherend) != + if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->otherend) != XenbusStateInitialised) goto out; @@ -374,7 +374,7 @@ static int xen_pcibk_reconfigure(struct xen_pcibk_device *pdev, dev_dbg(&pdev->xdev->dev, "Reconfiguring device ...\n"); mutex_lock(&pdev->dev_lock); - if (xenbus_read_driver_state(pdev->xdev->nodename) != state) + if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename) != state) goto out; err = xenbus_scanf(XBT_NIL, pdev->xdev->nodename, "num_devs", "%d", @@ -572,7 +572,7 @@ static int xen_pcibk_setup_backend(struct xen_pcibk_device *pdev) /* It's possible we could get the call to setup twice, so make sure * we're not already connected. */ - if (xenbus_read_driver_state(pdev->xdev->nodename) != + if (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename) != XenbusStateInitWait) goto out; @@ -662,7 +662,7 @@ static void xen_pcibk_be_watch(struct xenbus_watch *watch, struct xen_pcibk_device *pdev = container_of(watch, struct xen_pcibk_device, be_watch); - switch (xenbus_read_driver_state(pdev->xdev->nodename)) { + switch (xenbus_read_driver_state(pdev->xdev, pdev->xdev->nodename)) { case XenbusStateInitWait: xen_pcibk_setup_backend(pdev); break; diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c index 2dc874fb5506..6ed0cd8e9676 100644 --- a/drivers/xen/xenbus/xenbus_client.c +++ b/drivers/xen/xenbus/xenbus_client.c @@ -936,7 +936,8 @@ static int xenbus_unmap_ring_hvm(struct xenbus_device *dev, void *vaddr) * Returns: the state of the driver rooted at the given store path, or * XenbusStateUnknown if no state can be read. */ -enum xenbus_state xenbus_read_driver_state(const char *path) +enum xenbus_state xenbus_read_driver_state(const struct xenbus_device *dev, + const char *path) { enum xenbus_state result; int err = xenbus_gather(XBT_NIL, path, "state", "%d", &result, NULL); diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c index 86fe6e779056..d4f1dbf7cbc4 100644 --- a/drivers/xen/xenbus/xenbus_probe.c +++ b/drivers/xen/xenbus/xenbus_probe.c @@ -191,7 +191,7 @@ void xenbus_otherend_changed(struct xenbus_watch *watch, return; } - state = xenbus_read_driver_state(dev->otherend); + state = xenbus_read_driver_state(dev, dev->otherend); dev_dbg(&dev->dev, "state is %d, (%s), %s, %s\n", state, xenbus_strstate(state), dev->otherend_watch.node, path); @@ -364,7 +364,7 @@ void xenbus_dev_remove(struct device *_dev) * closed. */ if (!drv->allow_rebind || - xenbus_read_driver_state(dev->nodename) == XenbusStateClosing) + xenbus_read_driver_state(dev, dev->nodename) == XenbusStateClosing) xenbus_switch_state(dev, XenbusStateClosed); } EXPORT_SYMBOL_GPL(xenbus_dev_remove); @@ -514,7 +514,7 @@ int xenbus_probe_node(struct xen_bus_type *bus, size_t stringlen; char *tmpstring; - enum xenbus_state state = xenbus_read_driver_state(nodename); + enum xenbus_state state = xenbus_read_driver_state(NULL, nodename); if (state != XenbusStateInitialising) { /* Device is not new, so ignore it. This can happen if a diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c b/drivers/xen/xenbus/xenbus_probe_frontend.c index 6d1819269cbe..41832994f8b1 100644 --- a/drivers/xen/xenbus/xenbus_probe_frontend.c +++ b/drivers/xen/xenbus/xenbus_probe_frontend.c @@ -255,7 +255,7 @@ static int print_device_status(struct device *dev, void *data) } else if (xendev->state < XenbusStateConnected) { enum xenbus_state rstate = XenbusStateUnknown; if (xendev->otherend) - rstate = xenbus_read_driver_state(xendev->otherend); + rstate = xenbus_read_driver_state(xendev, xendev->otherend); pr_warn("Timeout connecting to device: %s (local state %d, remote state %d)\n", xendev->nodename, xendev->state, rstate); } diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index c94caf852aea..15319da65b7f 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -228,7 +228,8 @@ int xenbus_unmap_ring_vfree(struct xenbus_device *dev, void *vaddr); int xenbus_alloc_evtchn(struct xenbus_device *dev, evtchn_port_t *port); int xenbus_free_evtchn(struct xenbus_device *dev, evtchn_port_t port); -enum xenbus_state xenbus_read_driver_state(const char *path); +enum xenbus_state xenbus_read_driver_state(const struct xenbus_device *dev, + const char *path); __printf(3, 4) void xenbus_dev_error(struct xenbus_device *dev, int err, const char *fmt, ...); -- 2.53.0
From 0292f843bff05c1b266c32e9e802ca3f01e030f0 Mon Sep 17 00:00:00 2001 From: Juergen Gross <[email protected]> Date: Mon, 26 Jan 2026 08:45:17 +0100 Subject: [PATCH 2/2] xen/xenbus: better handle backend crash MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When the backend domain crashes, coordinated device cleanup is not possible (as it involves waiting for the backend state change). In that case, toolstack forcefully removes frontend xenstore entries. xenbus_dev_changed() handles this case, and triggers device cleanup. It's possible that toolstack manages to connect new device in that place, before xenbus_dev_changed() notices the old one is missing. If that happens, new one won't be probed and will forever remain in XenbusStateInitialising. Fix this by checking the frontend's state in Xenstore. In case it has been reset to XenbusStateInitialising by Xen tools, consider this being the result of an unplug+plug operation. It's important that cleanup on such unplug doesn't modify Xenstore entries (especially the "state" key) as it belong to the new device to be probed - changing it would derail establishing connection to the new backend (most likely, closing the device before it was even connected). Handle this case by setting new xenbus_device->vanished flag to true, and check it before changing state entry. And even if xenbus_dev_changed() correctly detects the device was forcefully removed, the cleanup handling is still racy. Since this whole handling doesn't happened in a single Xenstore transaction, it's possible that toolstack might put a new device there already. Avoid re-creating the state key (which in the case of loosing the race would actually close newly attached device). The problem does not apply to frontend domain crash, as this case involves coordinated cleanup. Problem originally reported at https://lore.kernel.org/xen-devel/aOZvivyZ9YhVWDLN@mail-itl/T/#t, including reproduction steps. Based-on-patch-by: Marek Marczykowski-Górecki <[email protected]> Signed-off-by: Juergen Gross <[email protected]> --- drivers/xen/xenbus/xenbus_client.c | 13 +++++++++-- drivers/xen/xenbus/xenbus_probe.c | 36 ++++++++++++++++++++++++++++++ include/xen/xenbus.h | 1 + 3 files changed, 48 insertions(+), 2 deletions(-) diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c index 6ed0cd8e9676..00ee8f62c28c 100644 --- a/drivers/xen/xenbus/xenbus_client.c +++ b/drivers/xen/xenbus/xenbus_client.c @@ -226,8 +226,9 @@ __xenbus_switch_state(struct xenbus_device *dev, struct xenbus_transaction xbt; int current_state; int err, abort; + bool vanished = false; - if (state == dev->state) + if (state == dev->state || dev->vanished) return 0; again: @@ -242,6 +243,10 @@ __xenbus_switch_state(struct xenbus_device *dev, err = xenbus_scanf(xbt, dev->nodename, "state", "%d", ¤t_state); if (err != 1) goto abort; + if (current_state != dev->state && current_state == XenbusStateInitialising) { + vanished = true; + goto abort; + } err = xenbus_printf(xbt, dev->nodename, "state", "%d", state); if (err) { @@ -256,7 +261,7 @@ __xenbus_switch_state(struct xenbus_device *dev, if (err == -EAGAIN && !abort) goto again; xenbus_switch_fatal(dev, depth, err, "ending transaction"); - } else + } else if (!vanished) dev->state = state; return 0; @@ -940,6 +945,10 @@ enum xenbus_state xenbus_read_driver_state(const struct xenbus_device *dev, const char *path) { enum xenbus_state result; + + if (dev && dev->vanished) + return XenbusStateUnknown; + int err = xenbus_gather(XBT_NIL, path, "state", "%d", &result, NULL); if (err) result = XenbusStateUnknown; diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c index d4f1dbf7cbc4..47e992032014 100644 --- a/drivers/xen/xenbus/xenbus_probe.c +++ b/drivers/xen/xenbus/xenbus_probe.c @@ -444,6 +444,9 @@ static void xenbus_cleanup_devices(const char *path, struct bus_type *bus) info.dev = NULL; bus_for_each_dev(bus, NULL, &info, cleanup_dev); if (info.dev) { + dev_warn(&info.dev->dev, + "device forcefully removed from xenstore\n"); + info.dev->vanished = true; device_unregister(&info.dev->dev); put_device(&info.dev->dev); } @@ -659,6 +662,39 @@ void xenbus_dev_changed(const char *node, struct xen_bus_type *bus) return; dev = xenbus_device_find(root, &bus->bus); + /* + * Backend domain crash results in not coordinated frontend removal, + * without going through XenbusStateClosing. If this is a new instance + * of the same device Xen tools will have reset the state to + * XenbusStateInitializing. + * It might be that the backend crashed early during the init phase of + * device setup, in which case the known state would have been + * XenbusStateInitializing. So test the backend domid to match the + * saved one. In case the new backend happens to have the same domid as + * the old one, we can just carry on, as there is no inconsistency + * resulting in this case. + */ + if (dev && !strcmp(bus->root, "device")) { + enum xenbus_state state = xenbus_read_driver_state(dev, dev->nodename); + unsigned int backend = xenbus_read_unsigned(root, "backend-id", + dev->otherend_id); + + if (state == XenbusStateInitialising && + (state != dev->state || backend != dev->otherend_id)) { + /* + * State has been reset, assume the old one vanished + * and new one needs to be probed. + */ + dev_warn(&dev->dev, + "state reset occurred, reconnecting\n"); + dev->vanished = true; + } + if (dev->vanished) { + device_unregister(&dev->dev); + put_device(&dev->dev); + dev = NULL; + } + } if (!dev) xenbus_probe_node(bus, type, root); else diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index 15319da65b7f..8ca15743af7f 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -80,6 +80,7 @@ struct xenbus_device { const char *devicetype; const char *nodename; const char *otherend; + bool vanished; int otherend_id; struct xenbus_watch otherend_watch; struct device dev; -- 2.53.0
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