[PATCH v2 rfc 0/3] resolve controller delete hang due to ongoing mpath I/O

[Sagi Grimberg]

Changes from v1:
- Rename states to NVME_CTRL_DELETING and NVME_CTRL_DELETING_NOIO to better
  describe the states
- Added prep patch to split nvme_remove_namespaces to _prep_ and _do_
- Added prep patch to provide some documentation about the states

A deadlock happens in the following scenario with multipath:
1) scan_work(nvme0) detects a new nsid while nvme0
    is an optimized path to it, path nvme1 happens to be
    inaccessible.

2) Before scan_work is complete nvme0 disconnect is initiated
    nvme_delete_ctrl_sync() sets nvme0 state to NVME_CTRL_DELETING

3) scan_work(1) attempts to submit IO,
    but nvme_path_is_optimized() observes nvme0 is not LIVE.
    Since nvme1 is a possible path IO is requeued and scan_work hangs.

4) Delete also hangs in flush_work(ctrl->scan_work)
    from nvme_remove_namespaces().

Similiarly a deadlock with ana_work may happen: if ana_work has started
and calls nvme_mpath_set_live and device_add_disk, it will
trigger I/O. When we trigger disconnect I/O will block because
our accessible (optimized) path is disconnecting, but the alternate
path is inaccessible, so I/O blocks. Then disconnect tries to flush
the ana_work and hangs.

This patchset alters the nvme states to address this deadlock condition.

Feedback is welcome.

Sagi Grimberg (3):
  nvme: split nvme_remove_namespaces
  nvme: document nvme controller states
  nvme-core: fix deadlock in disconnect during scan_work and/or ana_work

 drivers/nvme/host/core.c      | 45 +++++++++++++++++++++++++++--------
 drivers/nvme/host/fc.c        |  1 +
 drivers/nvme/host/multipath.c | 13 +++++++++-
 drivers/nvme/host/nvme.h      | 23 +++++++++++++++++-
 drivers/nvme/host/pci.c       |  4 +++-
 drivers/nvme/host/rdma.c      | 10 ++++----
 drivers/nvme/host/tcp.c       | 15 +++++++-----
 7 files changed, 88 insertions(+), 23 deletions(-)

-- 
2.25.1