Date: Sat, 3 Mar 2012 12:08:48 +0100 From: Hans Petter Selasky <hselasky@c2i.net> To: freebsd-scsi@freebsd.org, Alexander Motin <mav@freebsd.org>, gibbs@freebsd.org, freebsd-current@freebsd.org Subject: CAM detach races with USB memory sticks Message-ID: <201203031208.48514.hselasky@c2i.net>
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Hi,
I've started looking into some attach/detach stress tests for USB mass storage devices.
During my bughunting I've found the following issue:
In /sys/cam/cam_xpt.c:
4569 void
4570 xpt_release_device(struct cam_ed *device)
4571 {
4572
4573 mjacob 224806 if (device->refcount == 1) {
4574 gibbs 39212 struct cam_devq *devq;
4575
4576 gibbs 44500 if (device->alloc_ccb_entry.pinfo.index != CAM_UNQUEUED_INDEX
4577 || device->send_ccb_entry.pinfo.index != CAM_UNQUEUED_INDEX)
4578 panic("Removing device while still queued for ccbs");
4579 gibbs 49927
4580 if ((device->flags & CAM_DEV_REL_TIMEOUT_PENDING) != 0)
XXXX HERE XXXX
4581 mjacob 224806 callout_stop(&device->callout);
4583 mav 198748 TAILQ_REMOVE(&device->target->ed_entries, device,links);
4584 device->target->generation++;
4585 device->target->bus->sim->max_ccbs -= device->ccbq.devq_openings;
4586 trasz 186184 /* Release our slot in the devq */
4587 mav 198748 devq = device->target->bus->sim->devq;
4588 trasz 186184 cam_devq_resize(devq, devq->alloc_queue.array_size - 1);
4589 avatar 147571 camq_fini(&device->drvq);
4590 mav 198377 cam_ccbq_fini(&device->ccbq);
4591 ken 230590 /*
4592 * Free allocated memory. free(9) does nothing if the
4593 * supplied pointer is NULL, so it is safe to call without
4594 * checking.
4595 */
4596 free(device->supported_vpds, M_CAMXPT);
4597 free(device->device_id, M_CAMXPT);
4598 free(device->physpath, M_CAMXPT);
4599 free(device->rcap_buf, M_CAMXPT);
4600 free(device->serial_num, M_CAMXPT);
4601
4602 mav 198748 xpt_release_target(device->target);
4603 avatar 147723 free(device, M_CAMXPT);
Remember our OS is SMP now, so callout_drain() must be used on all callouts before
the structure where they are located are freed. Above I only see callout_stop(). The
problem is that xpt_release_device() appears to be called locked and callout_drain()
requires unlocked context! How do we solve this? I don't know so much about the CAM
layer and I hope that someone who does can give a hand here.
--HPS
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