device-core: use RCU for list of children of a bus
This fixes the race between device emulation code that tries to find a child device to dispatch the request to (e.g a scsi disk), and hotplug of a new device to that bus. Note that this doesn't convert all the readers of the list but only these that might go over that list without BQL held. This is a very small first step to make this code thread safe. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Message-Id: <20200913160259.32145-5-mlevitsk@redhat.com> [Use RCU_READ_LOCK_GUARD in more places, adjust testcase now that the delay in DEVICE_DELETED due to RCU is more consistent. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20201006123904.610658-9-mlevitsk@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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@ -49,7 +49,8 @@ int qbus_walk_children(BusState *bus,
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}
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}
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QTAILQ_FOREACH(kid, &bus->children, sibling) {
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WITH_RCU_READ_LOCK_GUARD() {
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QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) {
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err = qdev_walk_children(kid->child,
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pre_devfn, pre_busfn,
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post_devfn, post_busfn, opaque);
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@ -57,6 +58,7 @@ int qbus_walk_children(BusState *bus,
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return err;
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}
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}
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}
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if (post_busfn) {
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err = post_busfn(bus, opaque);
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@ -90,9 +92,11 @@ static void bus_reset_child_foreach(Object *obj, ResettableChildCallback cb,
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BusState *bus = BUS(obj);
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BusChild *kid;
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QTAILQ_FOREACH(kid, &bus->children, sibling) {
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WITH_RCU_READ_LOCK_GUARD() {
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QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) {
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cb(OBJECT(kid->child), opaque, type);
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}
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}
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}
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static void qbus_init(BusState *bus, DeviceState *parent, const char *name)
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@ -194,10 +198,12 @@ static void bus_set_realized(Object *obj, bool value, Error **errp)
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/* TODO: recursive realization */
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} else if (!value && bus->realized) {
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QTAILQ_FOREACH(kid, &bus->children, sibling) {
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WITH_RCU_READ_LOCK_GUARD() {
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QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) {
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DeviceState *dev = kid->child;
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qdev_unrealize(dev);
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}
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}
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if (bc->unrealize) {
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bc->unrealize(bus);
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}
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@ -51,6 +51,12 @@ const VMStateDescription *qdev_get_vmsd(DeviceState *dev)
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return dc->vmsd;
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}
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static void bus_free_bus_child(BusChild *kid)
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{
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object_unref(OBJECT(kid->child));
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g_free(kid);
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}
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static void bus_remove_child(BusState *bus, DeviceState *child)
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{
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BusChild *kid;
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@ -60,15 +66,16 @@ static void bus_remove_child(BusState *bus, DeviceState *child)
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char name[32];
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snprintf(name, sizeof(name), "child[%d]", kid->index);
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QTAILQ_REMOVE(&bus->children, kid, sibling);
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QTAILQ_REMOVE_RCU(&bus->children, kid, sibling);
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bus->num_children--;
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/* This gives back ownership of kid->child back to us. */
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object_property_del(OBJECT(bus), name);
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object_unref(OBJECT(kid->child));
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g_free(kid);
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return;
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/* free the bus kid, when it is safe to do so*/
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call_rcu(kid, bus_free_bus_child, rcu);
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break;
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}
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}
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}
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@ -83,7 +90,7 @@ static void bus_add_child(BusState *bus, DeviceState *child)
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kid->child = child;
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object_ref(OBJECT(kid->child));
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QTAILQ_INSERT_HEAD(&bus->children, kid, sibling);
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QTAILQ_INSERT_HEAD_RCU(&bus->children, kid, sibling);
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/* This transfers ownership of kid->child to the property. */
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snprintf(name, sizeof(name), "child[%d]", kid->index);
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@ -672,7 +679,8 @@ DeviceState *qdev_find_recursive(BusState *bus, const char *id)
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DeviceState *ret;
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BusState *child;
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QTAILQ_FOREACH(kid, &bus->children, sibling) {
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WITH_RCU_READ_LOCK_GUARD() {
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QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) {
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DeviceState *dev = kid->child;
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if (dev->id && strcmp(dev->id, id) == 0) {
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@ -686,6 +694,7 @@ DeviceState *qdev_find_recursive(BusState *bus, const char *id)
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}
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}
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}
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}
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return NULL;
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}
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@ -400,7 +400,10 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r)
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id = r->req.dev->id;
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found_lun0 = false;
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n = 0;
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QTAILQ_FOREACH(kid, &r->req.bus->qbus.children, sibling) {
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RCU_READ_LOCK_GUARD();
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QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) {
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DeviceState *qdev = kid->child;
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SCSIDevice *dev = SCSI_DEVICE(qdev);
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@ -421,7 +424,7 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r)
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memset(r->buf, 0, len);
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stl_be_p(&r->buf[0], n);
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i = found_lun0 ? 8 : 16;
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QTAILQ_FOREACH(kid, &r->req.bus->qbus.children, sibling) {
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QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) {
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DeviceState *qdev = kid->child;
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SCSIDevice *dev = SCSI_DEVICE(qdev);
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@ -430,6 +433,7 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r)
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i += 8;
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}
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}
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assert(i == n + 8);
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r->len = len;
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return true;
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@ -1572,7 +1576,8 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun)
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BusChild *kid;
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SCSIDevice *target_dev = NULL;
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QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) {
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RCU_READ_LOCK_GUARD();
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QTAILQ_FOREACH_RCU(kid, &bus->qbus.children, sibling) {
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DeviceState *qdev = kid->child;
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SCSIDevice *dev = SCSI_DEVICE(qdev);
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@ -1591,6 +1596,7 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun)
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}
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}
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}
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return target_dev;
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}
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@ -367,12 +367,16 @@ static int virtio_scsi_do_tmf(VirtIOSCSI *s, VirtIOSCSIReq *req)
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case VIRTIO_SCSI_T_TMF_I_T_NEXUS_RESET:
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target = req->req.tmf.lun[1];
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s->resetting++;
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QTAILQ_FOREACH(kid, &s->bus.qbus.children, sibling) {
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rcu_read_lock();
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QTAILQ_FOREACH_RCU(kid, &s->bus.qbus.children, sibling) {
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d = SCSI_DEVICE(kid->child);
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if (d->channel == 0 && d->id == target) {
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qdev_reset_all(&d->qdev);
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}
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}
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rcu_read_unlock();
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s->resetting--;
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break;
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@ -3,6 +3,8 @@
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#include "qemu/queue.h"
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#include "qemu/bitmap.h"
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#include "qemu/rcu.h"
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#include "qemu/rcu_queue.h"
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#include "qom/object.h"
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#include "hw/hotplug.h"
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#include "hw/resettable.h"
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@ -238,6 +240,7 @@ struct BusClass {
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};
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typedef struct BusChild {
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struct rcu_head rcu;
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DeviceState *child;
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int index;
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QTAILQ_ENTRY(BusChild) sibling;
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@ -258,6 +261,12 @@ struct BusState {
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int max_index;
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bool realized;
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int num_children;
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/*
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* children is a RCU QTAILQ, thus readers must use RCU to access it,
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* and writers must hold the big qemu lock
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*/
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QTAILQ_HEAD(, BusChild) children;
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QLIST_ENTRY(BusState) sibling;
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ResettableState reset;
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