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device-core: use RCU for list of children of a bus

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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>
This commit is contained in:
Maxim Levitsky 2020-10-06 15:38:59 +03:00 • committed by Paolo Bonzini
parent 7bed89958b
commit 2d24a64661
5 changed files with 63 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

12
hw/scsi/scsi-bus.c
View file

@ -400,7 +400,10 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r)
id = r->req.dev->id;
found_lun0 = false;
n = 0;
QTAILQ_FOREACH(kid, &r->req.bus->qbus.children, sibling) {
RCU_READ_LOCK_GUARD();
QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) {
DeviceState *qdev = kid->child;
SCSIDevice *dev = SCSI_DEVICE(qdev);
@ -421,7 +424,7 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r)
memset(r->buf, 0, len);
stl_be_p(&r->buf[0], n);
i = found_lun0 ? 8 : 16;
QTAILQ_FOREACH(kid, &r->req.bus->qbus.children, sibling) {
QTAILQ_FOREACH_RCU(kid, &r->req.bus->qbus.children, sibling) {
DeviceState *qdev = kid->child;
SCSIDevice *dev = SCSI_DEVICE(qdev);
@ -430,6 +433,7 @@ static bool scsi_target_emulate_report_luns(SCSITargetReq *r)
i += 8;
}
}
assert(i == n + 8);
r->len = len;
return true;
@ -1572,7 +1576,8 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun)
BusChild *kid;
SCSIDevice *target_dev = NULL;
QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) {
RCU_READ_LOCK_GUARD();
QTAILQ_FOREACH_RCU(kid, &bus->qbus.children, sibling) {
DeviceState *qdev = kid->child;
SCSIDevice *dev = SCSI_DEVICE(qdev);
@ -1591,6 +1596,7 @@ SCSIDevice *scsi_device_find(SCSIBus *bus, int channel, int id, int lun)
}
}
}
return target_dev;
}

6
hw/scsi/virtio-scsi.c
View file

@ -367,12 +367,16 @@ static int virtio_scsi_do_tmf(VirtIOSCSI *s, VirtIOSCSIReq *req)
case VIRTIO_SCSI_T_TMF_I_T_NEXUS_RESET:
target = req->req.tmf.lun[1];
s->resetting++;
QTAILQ_FOREACH(kid, &s->bus.qbus.children, sibling) {
rcu_read_lock();
QTAILQ_FOREACH_RCU(kid, &s->bus.qbus.children, sibling) {
d = SCSI_DEVICE(kid->child);
if (d->channel == 0 && d->id == target) {
qdev_reset_all(&d->qdev);
}
}
rcu_read_unlock();
s->resetting--;
break;