Heinz Graalfs <graalfs@xxxxxxxxxxxxxxxxxx> writes: > On 23/01/14 05:51, Rusty Russell wrote: >> Heinz Graalfs <graalfs@xxxxxxxxxxxxxxxxxx> writes: >>> Hi, here is my v4 patch-set update to the v3 RFC submitted on Nov 27th. >> >> Hi Heinz, >> >> I didn't get a response on my 'break all the virtqueues' patch >> series. Could your System Z code work with this? >> >> Rusty. >> >> > > Sorry Rusty, I'm back as of today. > > I applied your patch series and did some testing... > > Removing a disk while reading from it mostly still ends up > in hangs as of below: OK, we still have the problem of in-flight requests. I think the correct answer is to drop all requests if the virtqueue is broken: - blk_cleanup_queue(vblk->disk->queue); + if (virtqueue_is_broken(vblk->vq)) + /* Don't wait for completion, just drop queue. */ + blk_abandon_queue(vblk->disk->queue); + else + blk_cleanup_queue(vblk->disk->queue); + Unfortunately blk_abandon_queue() doesn't exist. Your previous patch did nothing in that path, which I suspect may leak memory. That may be acceptable given that this Shouldn't Happen (often). At this point, I ask Jens :) Cheers, Rusty. > > PID: 13 TASK: 163f8000 CPU: 0 COMMAND: "kworker/u128:1" > #0 [163f72e0] __schedule at 6aa22c > #1 [163f7428] io_schedule at 6aab6c > #2 [163f7448] sleep_on_page at 22cbb2 > #3 [163f7460] __wait_on_bit at 6ab394 > #4 [163f74b0] wait_on_page_bit at 22cef4 > #5 [163f7508] filemap_fdatawait_range at 22d0a6 > #6 [163f75e8] filemap_write_and_wait at 22de62 > #7 [163f7618] fsync_bdev at 2dc5d8 > #8 [163f7640] invalidate_partition at 407ba8 > #9 [163f7668] del_gendisk at 408a4c > #10 [163f76c0] virtblk_remove at 46f81e > #11 [163f76f8] virtio_dev_remove at 43d302 > #12 [163f7730] __device_release_driver at 4604c4 > #13 [163f7758] device_release_driver at 46057c > #14 [163f7780] bus_remove_device at 45ff74 > #15 [163f77b0] device_del at 45cf54 > #16 [163f77e8] device_unregister at 45d00e > #17 [163f7808] unregister_virtio_device at 43d5ba > #18 [163f7828] virtio_ccw_remove at 55156c > #19 [163f7850] ccw_device_remove at 4d7e22 > #20 [163f78d8] __device_release_driver at 4604c4 > #21 [163f7900] device_release_driver at 46057c > #22 [163f7928] bus_remove_device at 45ff74 > #23 [163f7958] device_del at 45cf54 > #24 [163f7990] ccw_device_unregister at 4d86a0 > #25 [163f79b0] io_subchannel_remove at 4d8d1a > #26 [163f79e8] css_remove at 4d2856 > #27 [163f7a08] __device_release_driver at 4604c4 > #28 [163f7a30] device_release_driver at 46057c > #29 [163f7a58] bus_remove_device at 45ff74 > #30 [163f7a88] device_del at 45cf54 > #31 [163f7ac0] device_unregister at 45d00e > #32 [163f7ae0] css_sch_device_unregister at 4d29d4 > #33 [163f7b08] io_subchannel_sch_event at 4daad6 > #34 [163f7b80] css_evaluate_known_subchannel at 4d2cc0 > #35 [163f7be0] slow_eval_known_fn at 4d3cea > #36 [163f7c10] bus_for_each_dev at 45ea56 > #37 [163f7c50] for_each_subchannel_staged at 4d337e > #38 [163f7c98] css_slow_path_func at 4d3450 > #39 [163f7cc0] process_one_work at 164ff4 > #40 [163f7d60] worker_thread at 166500 > #41 [163f7da8] kthread at 16e67c > #42 [163f7eb0] kernel_thread_starter at 6b0a5e > > Removing a disk while writing to it now ends up mostly > with errors (which is new behavior and good). > However, the detached device is still listed under /dev, and a > subsequent umount ends up in a hang. Latter also occurred with > my approach, sometimes. > > Sometimes everything ends up in QEMU crashes, which is, however, not > reproducible. I will investigate on this. > > Heinz > >>> When an active virtio block device is hot-unplugged from a KVM guest, >>> affected guest user applications are not aware of any errors that occur >>> due to the lost device. This patch-set adds code to avoid further request >>> queueing when a lost block device is detected, resulting in appropriate >>> error info. Additionally a potential hang situation can be avoided by not >>> waiting for requests (e.g. in-flight requests) in blk_cleanup_queue() that >>> will never complete. >>> >>> On System z there exists no handshake mechanism between host and guest >>> when a device is hot-unplugged. The device is removed and no further I/O >>> is possible. >>> >>> When an online channel device disappears on System z the kernel's CIO layer >>> informs the driver (virtio_ccw) about the lost device. >>> >>> Here are some more error details: >>> >>> For a particular block device virtio's request function virtblk_request() >>> is called by the block layer to queue requests to be handled by the host. >>> In case of a lost device requests can still be queued, but an appropriate >>> subsequent host kick usually fails. This leads to situations where no error >>> feedback is shown. >>> >>> In order to prevent request queueing for lost devices appropriate settings >>> in the block layer should be made. Exploiting System z's CIO notify handler >>> callback, and passing on device loss information via the surprize_removal >>> flag to the remove callback of the backend driver, can solve this task. >>> >>> v3->v4 changes: >>> - patch 1: solves some vcdev pointer handling issues in the virtio_ccw driver >>> (e.g. locked vcdev pointer reset/query; serialize remove()/set_offline() >>> callback processing). >>> - patch 2: introduces 'device_lost' atomic in virtio_device and use in >>> backend driver virtio_blk accordingly (original 3 patches merged). >>> - patch 3: the notify() callback is now serialized with remove()/set_offline() >>> callbacks. The notification is ignored if the vcdev pointer has been cleared >>> already (by remove() or set_offline()). >>> >>> v2->v3 changes: >>> - remove virtio_driver's notify callback (and appropriate code) introduced >>> in my v1 RFC >>> - introduce 'surprize_removal' in struct virtio_device >>> - change virtio_blk's remove callback to perform special actions when the >>> surprize_removal flag is set >>> - avoid final I/O by preventing further request queueing >>> - avoid hangs in blk_cleanup_queue() due to waits on 'in-flight' requests >>> - set surprize_removal in virtio_ccw's notify callback when a device is lost >>> >>> v1->v2 changes: >>> - add include of linux/notifier.h (I also added it to the 3rd patch) >>> - get queue lock in order to be able to use safe queue_flag_set() functions >>> in virtblk_notify() handler >>> >>> >>> Heinz Graalfs (3): >>> virtio_ccw: fix vcdev pointer handling issues >>> virtio: introduce 'device_lost' flag in virtio_device >>> virtio_ccw: set 'device_lost' on CIO_GONE notification >>> >>> drivers/block/virtio_blk.c | 14 ++++++++++- >>> drivers/s390/kvm/virtio_ccw.c | 58 ++++++++++++++++++++++++++++++++++++------- >>> include/linux/virtio.h | 2 ++ >>> 3 files changed, 64 insertions(+), 10 deletions(-) >>> >>> -- >>> 1.8.3.1 >> _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
