On Thu, Jan 19, 2023 at 04:43:26PM -0500, Stefan Hajnoczi wrote: > When an IOThread is configured, the ctrl virtqueue is processed in the > IOThread. TMFs that reset SCSI devices are currently called directly > from the IOThread and trigger an assertion failure in blk_drain(): > > ../block/block-backend.c:1780: void blk_drain(BlockBackend *): Assertion > `qemu_in_main_thread()' failed. > > The blk_drain() function is not designed to be called from an IOThread > because it needs the Big QEMU Lock (BQL). > > This patch defers TMFs that reset SCSI devices to a Bottom Half (BH) > that runs in the main loop thread under the BQL. This way it's safe to > call blk_drain() and the assertion failure is avoided. > > Introduce s->tmf_bh_list for tracking TMF requests that have been > deferred to the BH. When the BH runs it will grab the entire list and > process all requests. Care must be taken to clear the list when the > virtio-scsi device is reset or unrealized. Otherwise deferred TMF > requests could execute later and lead to use-after-free or other > undefined behavior. > > The s->resetting counter that's used by TMFs that reset SCSI devices is > accessed from multiple threads. This patch makes that explicit by using > atomic accessor functions. With this patch applied the counter is only > modified by the main loop thread under the BQL but can be read by any > thread. > > Reported-by: Qing Wang <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Signed-off-by: Stefan Hajnoczi <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]> It's mostly a scsi thing so I guess SCSI tree is appropriate. Thanks! > --- > include/hw/virtio/virtio-scsi.h | 11 ++- > hw/scsi/virtio-scsi.c | 169 +++++++++++++++++++++++++------- > 2 files changed, 143 insertions(+), 37 deletions(-) > > diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h > index 37b75e15e3..779568ab5d 100644 > --- a/include/hw/virtio/virtio-scsi.h > +++ b/include/hw/virtio/virtio-scsi.h > @@ -74,13 +74,22 @@ struct VirtIOSCSICommon { > VirtQueue **cmd_vqs; > }; > > +struct VirtIOSCSIReq; > + > struct VirtIOSCSI { > VirtIOSCSICommon parent_obj; > > SCSIBus bus; > - int resetting; > + int resetting; /* written from main loop thread, read from any thread */ > bool events_dropped; > > + /* > + * TMFs deferred to main loop BH. These fields are protected by > + * virtio_scsi_acquire(). > + */ > + QEMUBH *tmf_bh; > + QTAILQ_HEAD(, VirtIOSCSIReq) tmf_bh_list; > + > /* Fields for dataplane below */ > AioContext *ctx; /* one iothread per virtio-scsi-pci for now */ > > diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c > index 2b649ca976..612c525d9d 100644 > --- a/hw/scsi/virtio-scsi.c > +++ b/hw/scsi/virtio-scsi.c > @@ -43,13 +43,11 @@ typedef struct VirtIOSCSIReq { > QEMUSGList qsgl; > QEMUIOVector resp_iov; > > - union { > - /* Used for two-stage request submission */ > - QTAILQ_ENTRY(VirtIOSCSIReq) next; > + /* Used for two-stage request submission and TMFs deferred to BH */ > + QTAILQ_ENTRY(VirtIOSCSIReq) next; > > - /* Used for cancellation of request during TMFs */ > - int remaining; > - }; > + /* Used for cancellation of request during TMFs */ > + int remaining; > > SCSIRequest *sreq; > size_t resp_size; > @@ -294,6 +292,122 @@ static inline void virtio_scsi_ctx_check(VirtIOSCSI *s, > SCSIDevice *d) > } > } > > +static void virtio_scsi_do_one_tmf_bh(VirtIOSCSIReq *req) > +{ > + VirtIOSCSI *s = req->dev; > + SCSIDevice *d = virtio_scsi_device_get(s, req->req.tmf.lun); > + BusChild *kid; > + int target; > + > + switch (req->req.tmf.subtype) { > + case VIRTIO_SCSI_T_TMF_LOGICAL_UNIT_RESET: > + if (!d) { > + req->resp.tmf.response = VIRTIO_SCSI_S_BAD_TARGET; > + goto out; > + } > + if (d->lun != virtio_scsi_get_lun(req->req.tmf.lun)) { > + req->resp.tmf.response = VIRTIO_SCSI_S_INCORRECT_LUN; > + goto out; > + } > + qatomic_inc(&s->resetting); > + device_cold_reset(&d->qdev); > + qatomic_dec(&s->resetting); > + break; > + > + case VIRTIO_SCSI_T_TMF_I_T_NEXUS_RESET: > + target = req->req.tmf.lun[1]; > + qatomic_inc(&s->resetting); > + > + rcu_read_lock(); > + QTAILQ_FOREACH_RCU(kid, &s->bus.qbus.children, sibling) { > + SCSIDevice *d1 = SCSI_DEVICE(kid->child); > + if (d1->channel == 0 && d1->id == target) { > + device_cold_reset(&d1->qdev); > + } > + } > + rcu_read_unlock(); > + > + qatomic_dec(&s->resetting); > + break; > + > + default: > + g_assert_not_reached(); > + break; > + } > + > +out: > + object_unref(OBJECT(d)); > + > + virtio_scsi_acquire(s); > + virtio_scsi_complete_req(req); > + virtio_scsi_release(s); > +} > + > +/* Some TMFs must be processed from the main loop thread */ > +static void virtio_scsi_do_tmf_bh(void *opaque) > +{ > + VirtIOSCSI *s = opaque; > + QTAILQ_HEAD(, VirtIOSCSIReq) reqs = QTAILQ_HEAD_INITIALIZER(reqs); > + VirtIOSCSIReq *req; > + VirtIOSCSIReq *tmp; > + > + GLOBAL_STATE_CODE(); > + > + virtio_scsi_acquire(s); > + > + QTAILQ_FOREACH_SAFE(req, &s->tmf_bh_list, next, tmp) { > + QTAILQ_REMOVE(&s->tmf_bh_list, req, next); > + QTAILQ_INSERT_TAIL(&reqs, req, next); > + } > + > + qemu_bh_delete(s->tmf_bh); > + s->tmf_bh = NULL; > + > + virtio_scsi_release(s); > + > + QTAILQ_FOREACH_SAFE(req, &reqs, next, tmp) { > + QTAILQ_REMOVE(&reqs, req, next); > + virtio_scsi_do_one_tmf_bh(req); > + } > +} > + > +static void virtio_scsi_reset_tmf_bh(VirtIOSCSI *s) > +{ > + VirtIOSCSIReq *req; > + VirtIOSCSIReq *tmp; > + > + GLOBAL_STATE_CODE(); > + > + virtio_scsi_acquire(s); > + > + if (s->tmf_bh) { > + qemu_bh_delete(s->tmf_bh); > + s->tmf_bh = NULL; > + } > + > + QTAILQ_FOREACH_SAFE(req, &s->tmf_bh_list, next, tmp) { > + QTAILQ_REMOVE(&s->tmf_bh_list, req, next); > + > + /* SAM-6 6.3.2 Hard reset */ > + req->resp.tmf.response = VIRTIO_SCSI_S_TARGET_FAILURE; > + virtio_scsi_complete_req(req); > + } > + > + virtio_scsi_release(s); > +} > + > +static void virtio_scsi_defer_tmf_to_bh(VirtIOSCSIReq *req) > +{ > + VirtIOSCSI *s = req->dev; > + > + QTAILQ_INSERT_TAIL(&s->tmf_bh_list, req, next); > + > + if (!s->tmf_bh) { > + s->tmf_bh = qemu_bh_new(virtio_scsi_do_tmf_bh, s); > + qemu_bh_schedule(s->tmf_bh); > + } > +} > + > /* Return 0 if the request is ready to be completed and return to guest; > * -EINPROGRESS if the request is submitted and will be completed later, in > the > * case of async cancellation. */ > @@ -301,8 +415,6 @@ static int virtio_scsi_do_tmf(VirtIOSCSI *s, > VirtIOSCSIReq *req) > { > SCSIDevice *d = virtio_scsi_device_get(s, req->req.tmf.lun); > SCSIRequest *r, *next; > - BusChild *kid; > - int target; > int ret = 0; > > virtio_scsi_ctx_check(s, d); > @@ -359,15 +471,9 @@ static int virtio_scsi_do_tmf(VirtIOSCSI *s, > VirtIOSCSIReq *req) > break; > > case VIRTIO_SCSI_T_TMF_LOGICAL_UNIT_RESET: > - if (!d) { > - goto fail; > - } > - if (d->lun != virtio_scsi_get_lun(req->req.tmf.lun)) { > - goto incorrect_lun; > - } > - s->resetting++; > - device_cold_reset(&d->qdev); > - s->resetting--; > + case VIRTIO_SCSI_T_TMF_I_T_NEXUS_RESET: > + virtio_scsi_defer_tmf_to_bh(req); > + ret = -EINPROGRESS; > break; > > case VIRTIO_SCSI_T_TMF_ABORT_TASK_SET: > @@ -410,22 +516,6 @@ static int virtio_scsi_do_tmf(VirtIOSCSI *s, > VirtIOSCSIReq *req) > } > break; > > - case VIRTIO_SCSI_T_TMF_I_T_NEXUS_RESET: > - target = req->req.tmf.lun[1]; > - s->resetting++; > - > - rcu_read_lock(); > - QTAILQ_FOREACH_RCU(kid, &s->bus.qbus.children, sibling) { > - SCSIDevice *d1 = SCSI_DEVICE(kid->child); > - if (d1->channel == 0 && d1->id == target) { > - device_cold_reset(&d1->qdev); > - } > - } > - rcu_read_unlock(); > - > - s->resetting--; > - break; > - > case VIRTIO_SCSI_T_TMF_CLEAR_ACA: > default: > req->resp.tmf.response = VIRTIO_SCSI_S_FUNCTION_REJECTED; > @@ -655,7 +745,7 @@ static void virtio_scsi_request_cancelled(SCSIRequest *r) > if (!req) { > return; > } > - if (req->dev->resetting) { > + if (qatomic_read(&req->dev->resetting)) { > req->resp.cmd.response = VIRTIO_SCSI_S_RESET; > } else { > req->resp.cmd.response = VIRTIO_SCSI_S_ABORTED; > @@ -831,9 +921,12 @@ static void virtio_scsi_reset(VirtIODevice *vdev) > VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev); > > assert(!s->dataplane_started); > - s->resetting++; > + > + virtio_scsi_reset_tmf_bh(s); > + > + qatomic_inc(&s->resetting); > bus_cold_reset(BUS(&s->bus)); > - s->resetting--; > + qatomic_dec(&s->resetting); > > vs->sense_size = VIRTIO_SCSI_SENSE_DEFAULT_SIZE; > vs->cdb_size = VIRTIO_SCSI_CDB_DEFAULT_SIZE; > @@ -1053,6 +1146,8 @@ static void virtio_scsi_device_realize(DeviceState > *dev, Error **errp) > VirtIOSCSI *s = VIRTIO_SCSI(dev); > Error *err = NULL; > > + QTAILQ_INIT(&s->tmf_bh_list); > + > virtio_scsi_common_realize(dev, > virtio_scsi_handle_ctrl, > virtio_scsi_handle_event, > @@ -1090,6 +1185,8 @@ static void virtio_scsi_device_unrealize(DeviceState > *dev) > { > VirtIOSCSI *s = VIRTIO_SCSI(dev); > > + virtio_scsi_reset_tmf_bh(s); > + > qbus_set_hotplug_handler(BUS(&s->bus), NULL); > virtio_scsi_common_unrealize(dev); > } > -- > 2.39.0
