Heinz Graalfs <graalfs@xxxxxxxxxxxxxxxxxx> writes: > On 17/12/13 04:42, Rusty Russell wrote: >> Heinz Graalfs <graalfs@xxxxxxxxxxxxxxxxxx> writes: >>> Hi, here is my v4 patch-set update to the v3 RFC submitted on Nov 27th. >>> >>> 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. >> >> >> Hi Heinz, >> >> If you simply mark every virtqueue as broken when this >> unexpected unplug happens, does that not Just Work? >> >> I think I've asked this before... >> Rusty. > > Hi Rusty, > > setting the (one) virtqueue, vblk is currently using, as broken doesn't > solve the problems. > > In that case virtblk_request()s still succeed - like this one... No, you set *all* virtqueues broken. Which is accurate, right? Cheers, Rusty. > > ([<0000000000112b28>] show_trace+0xf8/0x154) > [<0000000000112bde>] show_stack+0x5a/0xdc > [<000000000045eb56>] virtblk_request+0x25a/0x2b8 > [<00000000003e749c>] __blk_run_queue+0x50/0x64 > [<00000000003edb54>] blk_queue_bio+0x358/0x3f0 > [<00000000003eb446>] generic_make_request+0xea/0x130 > [<00000000003eb536>] submit_bio+0xaa/0x1a8 > [<00000000002c95e8>] _submit_bh+0x1c4/0x2f4 > [<00000000003a25e4>] journal_write_superblock+0xa0/0x1fc > [<00000000003a3ed4>] journal_update_sb_log_tail+0x48/0x7c > [<000000000039e742>] journal_commit_transaction+0x1586/0x1aa0 > [<00000000003a2a0e>] kjournald+0xfe/0x2a0 > [<00000000001786fc>] kthread+0xd8/0xe0 > [<0000000000698fee>] kernel_thread_starter+0x6/0xc > 2 locks held by kjournald/1984: > > ... and end up in hang situations ... > > PID: 13 TASK: 1e3f8000 CPU: 0 COMMAND: "kworker/u128:1" > #0 [1e2033e0] __schedule at 695ff2 > #1 [1e203530] log_wait_commit at 3a28a6 > #2 [1e2035a0] ext3_sync_fs at 328dea > #3 [1e2035d8] sync_filesystem at 2c785c > #4 [1e203600] fsync_bdev at 2d4650 > #5 [1e203628] invalidate_partition at 3f80c8 > #6 [1e203650] del_gendisk at 3f8f5c > #7 [1e2036c8] virtblk_remove at 45e60e > #8 [1e203700] virtio_dev_remove at 42d72e > #9 [1e203738] __device_release_driver at 44f0b0 > #10 [1e203760] device_release_driver at 44f16c > #11 [1e203788] bus_remove_device at 44ea92 > #12 [1e2037b8] device_del at 44bb40 > #13 [1e2037f0] device_unregister at 44bbfa > #14 [1e203810] unregister_virtio_device at 42d9e6 > #15 [1e203830] virtio_ccw_remove at 53b834 > #16 [1e203850] ccw_device_remove at 4c5bf6 > #17 [1e2038d8] __device_release_driver at 44f0b0 > #18 [1e203900] device_release_driver at 44f16c > #19 [1e203928] bus_remove_device at 44ea92 > #20 [1e203958] device_del at 44bb40 > #21 [1e203990] ccw_device_unregister at 4c645c > #22 [1e2039b0] io_subchannel_remove at 4c6b1a > #23 [1e2039e8] css_remove at 4c054e > #24 [1e203a08] __device_release_driver at 44f0b0 > #25 [1e203a30] device_release_driver at 44f16c > #26 [1e203a58] bus_remove_device at 44ea92 > #27 [1e203a88] device_del at 44bb40 > #28 [1e203ac0] device_unregister at 44bbfa > #29 [1e203ae0] css_sch_device_unregister at 4c06cc > #30 [1e203b08] io_subchannel_sch_event at 4c8c3a > #31 [1e203b80] css_evaluate_known_subchannel at 4c09bc > #32 [1e203be0] slow_eval_known_fn at 4c19a6 > #33 [1e203c10] bus_for_each_dev at 44d50e > #34 [1e203c50] for_each_subchannel_staged at 4c1066 > #35 [1e203c98] css_slow_path_func at 4c1124 > #36 [1e203cc0] process_one_work at 16c7f6 > #37 [1e203d60] worker_thread at 16dce4 > #38 [1e203da8] kthread at 1786fc > #39 [1e203eb0] kernel_thread_starter at 698fee > > Heinz > >> >>> >>> 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
