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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 10/17/25 19:54, Stefan Hajnoczi wrote: > On Fri, Oct 17, 2025 at 11:43:30AM +0200, Fiona Ebner wrote: >> Changes in v2: >> * Different approach, collect requests for cancelling in a list for a >> localized solution rather than keeping track of the lock status via >> function arguments. >> >> hw/scsi/virtio-scsi.c | 14 +++++++++++++- >> 1 file changed, 13 insertions(+), 1 deletion(-) > > Thanks, applied to my block tree: > https://gitlab.com/stefanha/qemu/commits/block Thanks Stefan; sorry for the delay in reviewing. The fix of releasing the lock around virtio_scsi_tmf_cancel_req(): diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c index 9b12ee7f1c6..ac17c97f224 100644 --- a/hw/scsi/scsi-bus.c +++ b/hw/scsi/scsi-bus.c @@ -1503,6 +1503,10 @@ SCSIRequest *scsi_req_ref(SCSIRequest *req) void scsi_req_unref(SCSIRequest *req) { + if (!req) { + return; + } + assert(req->refcount > 0); if (--req->refcount == 0) { BusState *qbus = req->dev->qdev.parent_bus; diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index d817fc42b4c..481e78e4771 100644 --- a/hw/scsi/virtio-scsi.c +++ b/hw/scsi/virtio-scsi.c @@ -364,7 +364,11 @@ static void virtio_scsi_do_tmf_aio_context(void *opaque) } WITH_QEMU_LOCK_GUARD(&d->requests_lock) { + SCSIRequest *prev = NULL; QTAILQ_FOREACH(r, &d->requests, next) { + scsi_req_unref(prev); + prev = NULL; + VirtIOSCSIReq *cmd_req = r->hba_private; assert(cmd_req); /* request has hba_private while enqueued */ @@ -374,8 +378,20 @@ static void virtio_scsi_do_tmf_aio_context(void *opaque) if (match_tag && cmd_req->req.cmd.tag != tmf->req.tmf.tag) { continue; } + + /* + * Keep it alive while the lock is released, and also to be + * able to read "next". + */ + scsi_req_ref(r); + prev = r; + + qemu_mutex_unlock(&d->request_lock); virtio_scsi_tmf_cancel_req(tmf, r); + qemu_mutex_lock(&d->request_lock); } + + scsi_req_unref(prev); } /* Incremented by virtio_scsi_do_tmf() */ would have a bug too, in that the loop is not using QTAILQ_FOREACH_SAFE and scsi_req_dequeue() removes the request from the list. I think scsi_req_ref/unref should also be changed to use atomics. free_request is only implemented by hw/usb/dev-uas.c and all the others do not need a lock, so we're fine with that. And QOM references held by the requests are not necessary, because anyway the requests won't survive scsi_qdev_unrealize (at which point the device is certainly alive). I'll test this, add some comments and send a patch: diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c index 9b12ee7f1c6..7fcacc178da 100644 --- a/hw/scsi/scsi-bus.c +++ b/hw/scsi/scsi-bus.c @@ -838,8 +838,6 @@ SCSIRequest *scsi_req_alloc(const SCSIReqOps *reqops, SCSIDevice *d, req->status = -1; req->host_status = -1; req->ops = reqops; - object_ref(OBJECT(d)); - object_ref(OBJECT(qbus->parent)); notifier_list_init(&req->cancel_notifiers); if (reqops->init_req) { @@ -1496,15 +1494,15 @@ void scsi_device_report_change(SCSIDevice *dev, SCSISense sense) SCSIRequest *scsi_req_ref(SCSIRequest *req) { - assert(req->refcount > 0); - req->refcount++; + assert(qatomic_read(&req->refcount) > 0); + qatomic_inc(&req->refcount); return req; } void scsi_req_unref(SCSIRequest *req) { - assert(req->refcount > 0); - if (--req->refcount == 0) { + assert(qatomic_read(&req->refcount) > 0); + if (qatomic_fetch_dec(&req->refcount) == 1) { BusState *qbus = req->dev->qdev.parent_bus; SCSIBus *bus = DO_UPCAST(SCSIBus, qbus, qbus); @@ -1514,8 +1512,6 @@ void scsi_req_unref(SCSIRequest *req) if (req->ops->free_req) { req->ops->free_req(req); } - object_unref(OBJECT(req->dev)); - object_unref(OBJECT(qbus->parent)); g_free(req); } } Paolo