On Fri, 2023-10-20 at 10:51 +0200, Juergen Gross wrote: > > > (qemu) device_del con1 > > [ 32.050919] ------------[ cut here ]------------ > > [ 32.050942] Trying to free already-free IRQ 33 > > [ 32.050990] WARNING: CPU: 0 PID: 51 at kernel/irq/manage.c:1895 __free_irq+0x1d4/0x330 > > > > Fix that by calling notifier_del_irq() first, which only calls > > free_irq() if the irq was requested in the first place. Then use > > I don't think the "if the irq was requested in the first place" is the correct > reasoning. > > I think the problem is that notifier_del_irq() will be called another time > through the .notifier_del hook. Two calls of notifier_del_irq() are fine, but > one call of it and another call of free_irq() via unbind_from_irqhandler() is > a problem. Er... yes, the HVC tty device still exists, can still be open and in use by userspace during the time that xencons_disconnect_backend() is running. Why does xencons_disconnect_backend() do all the evtchn and gnttab teardown *first* and then only call hvc_remove() at the end. That seems weird. So if I do 'dd if=/dev/zero of=/dev/hvc1' while I remove the device from qemu... yep, that seems to have filled the ring after the evtchn was torn down, and it's waiting for ever in domU_write_console(). In fact, that isn't *even* because of the race within xencons_disconnect_backend(). In xencons_backend_changed() when the backend goes into state XenbusStateClos{ing,ed} for the disconnect, we just set the frontend state directly to XenbusStateClosed without even *calling* xencons_disconnect_backend(). So we were *told* of the impending unplug. We fail to actually stop using the device, but we tell the backend that it's OK to go away. Oops :) The incremental patch below makes it work if I unplug a console while writing /dev/zero to it. But I suspect instead of calling xencons_disconnect_backend() when the backend changes to XenbusStateClos{ing,ed}, it should actually *just* do the hvc_close() part? The evtchn and gnttab cleanup should wait until the backend has actually finished closing? And what locking is there around xencons_disconnect_backend() anyway? Do we rely on the fact that it can all only happen from the xenstore watch thread? diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c index f0376612b267..0806078835f6 100644 --- a/drivers/tty/hvc/hvc_xen.c +++ b/drivers/tty/hvc/hvc_xen.c @@ -377,8 +377,10 @@ void xen_console_resume(void) #ifdef CONFIG_HVC_XEN_FRONTEND static void xencons_disconnect_backend(struct xencons_info *info) { + if (info->hvc != NULL) + hvc_remove(info->hvc); + info->hvc = NULL; if (info->irq > 0) { - notifier_del_irq(info->hvc, info->irq); evtchn_put(info->evtchn); info->irq = 0; info->evtchn = 0; @@ -390,9 +392,6 @@ static void xencons_disconnect_backend(struct xencons_info *info) if (info->gntref > 0) gnttab_free_grant_references(info->gntref); info->gntref = 0; - if (info->hvc != NULL) - hvc_remove(info->hvc); - info->hvc = NULL; } static void xencons_free(struct xencons_info *info) @@ -558,6 +557,7 @@ static void xencons_backend_changed(struct xenbus_device *dev, break; fallthrough; /* Missed the backend's CLOSING state */ case XenbusStateClosing: + xencons_disconnect_backend(dev_get_drvdata(&dev->dev)); xenbus_frontend_closed(dev); break; }
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