Well, this works for me (passes a test that gets into
the described scenario deteministically),
probably because we nvme_start_queues() earlier
in nvme_tcp_configure_io_queues().
Same is correct for rdma transport.

On Sun, Sep 19, 2021 at 01:19:39PM +0300, Sagi Grimberg wrote:

On 9/19/21 12:57 AM, Anton Eidelman wrote:

quoted

nvme_mpath_init_identify() invoked from nvme_init_identify()
fetches a fresh ANA log from the ctrl.
This is essential to have an up to date path states
for both existing namespaces and for those scan_work
may discover once the ctrl is up.

This happens in the following cases:
1) A new ctrl is being connected.
2) An existing ctrl is successfully reconnected.
3) An existing ctrl is being reset.

While in (1) ctrl->namespaces is empty, (2 & 3) may have namespaces,
and nvme_read_ana_log() may call nvme_update_ns_ana_state().

This result in a hang when the ANA state of an existing namespace
changes and makes the disk live: nvme_mpath_set_live() issues
IO to the namespace through the ctrl, which does NOT have IO queues yet.
See sample hang below.

Solution:
- move nvme_read_ana_log() call from nvme_mpath_init_identify()
into a separate function, nvme_mpath_update().
- call this function in nvme_start_ctrl() - here the ctrl is ready.

Downside: in case nvme_read_ana_log() fails, we do not find this out
   in nvme_mpath_init_identify().

Alernative solution:
   nvme_get_log() in nvme_mpath_init_identify(), but don't parse.
   Then nvme_start_ctrl() can just queue_work(nvme_wq, &ctrl->ana_work),
   along with scan_work.
   The ctrl->ana_log_buf contents is valid for scan_work,
   and ana_work will re-fetch and parse it.
   Downside: fetching an ANA log from the ctrl twice.

Sample failure:
     nvme nvme0: starting error recovery
     nvme nvme0: Reconnecting in 10 seconds...
     block nvme0n6: no usable path - requeuing I/O
     INFO: task kworker/u8:3:312 blocked for more than 122 seconds.
           Tainted: G            E     5.14.5-1.el7.elrepo.x86_64 #1
     Workqueue: nvme-wq nvme_tcp_reconnect_ctrl_work [nvme_tcp]
     Call Trace:
      __schedule+0x2a2/0x7e0
      schedule+0x4e/0xb0
      io_schedule+0x16/0x40
      wait_on_page_bit_common+0x15c/0x3e0
      do_read_cache_page+0x1e0/0x410
      read_cache_page+0x12/0x20
      read_part_sector+0x46/0x100
      read_lba+0x121/0x240
      efi_partition+0x1d2/0x6a0
      bdev_disk_changed.part.0+0x1df/0x430
      bdev_disk_changed+0x18/0x20
      blkdev_get_whole+0x77/0xe0
      blkdev_get_by_dev+0xd2/0x3a0
      __device_add_disk+0x1ed/0x310
      device_add_disk+0x13/0x20
      nvme_mpath_set_live+0x138/0x1b0 [nvme_core]
      nvme_update_ns_ana_state+0x2b/0x30 [nvme_core]
      nvme_update_ana_state+0xca/0xe0 [nvme_core]
      nvme_parse_ana_log+0xac/0x170 [nvme_core]
      nvme_read_ana_log+0x7d/0xe0 [nvme_core]
      nvme_mpath_init_identify+0x105/0x150 [nvme_core]
      nvme_init_identify+0x2df/0x4d0 [nvme_core]
      nvme_init_ctrl_finish+0x8d/0x3b0 [nvme_core]
      nvme_tcp_setup_ctrl+0x337/0x390 [nvme_tcp]
      nvme_tcp_reconnect_ctrl_work+0x24/0x40 [nvme_tcp]
      process_one_work+0x1bd/0x360
      worker_thread+0x50/0x3d0

Signed-off-by: Anton Eidelman <redacted>
---
  drivers/nvme/host/core.c      | 1 +
  drivers/nvme/host/multipath.c | 9 ++++++---
  drivers/nvme/host/nvme.h      | 4 ++++
  3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 97f8211cf92c..884ca1f6f80b 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c

@@ -4325,6 +4325,7 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
  	nvme_enable_aen(ctrl);
  	if (ctrl->queue_count > 1) {
+		nvme_mpath_update(ctrl);

Does this ordering now becomes subtle as it needs to run before we queue the
ns scan?

quoted

  		nvme_queue_scan(ctrl);
  		nvme_start_queues(ctrl);
  	}

_______________________________________________
Linux-nvme mailing list
Linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme