Merge tag 'block-6.1-2022-10-20' of git://git.kernel.dk/linux

Pull block fixes from Jens Axboe:

 - NVMe pull request via Christoph:
      - fix nvme-hwmon for DMA non-cohehrent architectures (Serge Semin)
      - add a nvme-hwmong maintainer (Christoph Hellwig)
      - fix error pointer dereference in error handling (Dan Carpenter)
      - fix invalid memory reference in nvmet_subsys_attr_qid_max_show
        (Daniel Wagner)
      - don't limit the DMA segment size in nvme-apple (Russell King)
      - fix workqueue MEM_RECLAIM flushing dependency (Sagi Grimberg)
      - disable write zeroes on various Kingston SSDs (Xander Li)

 - fix a memory leak with block device tracing (Ye)

 - flexible-array fix for ublk (Yushan)

 - document the ublk recovery feature from this merge window
   (ZiyangZhang)

 - remove dead bfq variable in struct (Yuwei)

 - error handling rq clearing fix (Yu)

 - add an IRQ safety check for the cached bio freeing (Pavel)

 - drbd bio cloning fix (Christoph)

* tag 'block-6.1-2022-10-20' of git://git.kernel.dk/linux:
  blktrace: remove unnessary stop block trace in 'blk_trace_shutdown'
  blktrace: fix possible memleak in '__blk_trace_remove'
  blktrace: introduce 'blk_trace_{start,stop}' helper
  bio: safeguard REQ_ALLOC_CACHE bio put
  block, bfq: remove unused variable for bfq_queue
  drbd: only clone bio if we have a backing device
  ublk_drv: use flexible-array member instead of zero-length array
  nvmet: fix invalid memory reference in nvmet_subsys_attr_qid_max_show
  nvmet: fix workqueue MEM_RECLAIM flushing dependency
  nvme-hwmon: kmalloc the NVME SMART log buffer
  nvme-hwmon: consistently ignore errors from nvme_hwmon_init
  nvme: add Guenther as nvme-hwmon maintainer
  nvme-apple: don't limit DMA segement size
  nvme-pci: disable write zeroes on various Kingston SSD
  nvme: fix error pointer dereference in error handling
  Documentation: document ublk user recovery feature
  blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping()

1 files changed, 36 insertions, 0 deletions

diff --git a/Documentation/block/ublk.rst b/Documentation/block/ublk.rst
index 2122d1a4a541..ba45c46cc0da 100644
--- a/Documentation/block/ublk.rst
+++ b/Documentation/block/ublk.rst
@@ -144,6 +144,42 @@ managing and controlling ublk devices with help of several control commands:
   For retrieving device info via ``ublksrv_ctrl_dev_info``. It is the server's
   responsibility to save IO target specific info in userspace.
 
+- ``UBLK_CMD_START_USER_RECOVERY``
+
+  This command is valid if ``UBLK_F_USER_RECOVERY`` feature is enabled. This
+  command is accepted after the old process has exited, ublk device is quiesced
+  and ``/dev/ublkc*`` is released. User should send this command before he starts
+  a new process which re-opens ``/dev/ublkc*``. When this command returns, the
+  ublk device is ready for the new process.
+
+- ``UBLK_CMD_END_USER_RECOVERY``
+
+  This command is valid if ``UBLK_F_USER_RECOVERY`` feature is enabled. This
+  command is accepted after ublk device is quiesced and a new process has
+  opened ``/dev/ublkc*`` and get all ublk queues be ready. When this command
+  returns, ublk device is unquiesced and new I/O requests are passed to the
+  new process.
+
+- user recovery feature description
+
+  Two new features are added for user recovery: ``UBLK_F_USER_RECOVERY`` and
+  ``UBLK_F_USER_RECOVERY_REISSUE``.
+
+  With ``UBLK_F_USER_RECOVERY`` set, after one ubq_daemon(ublk server's io
+  handler) is dying, ublk does not delete ``/dev/ublkb*`` during the whole
+  recovery stage and ublk device ID is kept. It is ublk server's
+  responsibility to recover the device context by its own knowledge.
+  Requests which have not been issued to userspace are requeued. Requests
+  which have been issued to userspace are aborted.
+
+  With ``UBLK_F_USER_RECOVERY_REISSUE`` set, after one ubq_daemon(ublk
+  server's io handler) is dying, contrary to ``UBLK_F_USER_RECOVERY``,
+  requests which have been issued to userspace are requeued and will be
+  re-issued to the new process after handling ``UBLK_CMD_END_USER_RECOVERY``.
+  ``UBLK_F_USER_RECOVERY_REISSUE`` is designed for backends who tolerate
+  double-write since the driver may issue the same I/O request twice. It
+  might be useful to a read-only FS or a VM backend.
+
 Data plane
 ----------