linux-kernel - [PATCH 0/3] cdev: Generic shutdown handling

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Date:   Wed, 20 Jan 2021 11:38:52 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     gregkh@...uxfoundation.org
Cc:     Ira Weiny <ira.weiny@...el.com>, Dave Jiang <dave.jiang@...el.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hans Verkuil <hans.verkuil@...co.com>, logang@...tatee.com,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: [PATCH 0/3] cdev: Generic shutdown handling

After reviewing driver submissions with new cdev + ioctl usages one
common stumbling block is coordinating the shutdown of the ioctl path,
or other file operations, at driver ->remove() time. While cdev_del()
guarantees that no new file descriptors will be established, operations
on existing file descriptors can proceed indefinitely.

Given the observation that the kernel spends the resources for a percpu_ref
per request_queue shared with all block_devices on a gendisk, do the
same for all the cdev instances that share the same
cdev_add()-to-cdev_del() lifetime.

With this in place cdev_del() not only guarantees 'no new opens', but it
also guarantees 'no new operations invocations' and 'all threads running
in an operation handler have exited that handler'.

As a proof point of the way driver implementations open-code around this
gap in the api the libnvdimm ioctl path is reworked with a result of:

    4 files changed, 101 insertions(+), 153 deletions(-)

---

Dan Williams (3):
      cdev: Finish the cdev api with queued mode support
      libnvdimm/ida: Switch to non-deprecated ida helpers
      libnvdimm/ioctl: Switch to cdev_register_queued()

 drivers/nvdimm/btt_devs.c       |    6 +
 drivers/nvdimm/bus.c            |  177 +++++++++------------------------------
 drivers/nvdimm/core.c           |   14 ++-
 drivers/nvdimm/dax_devs.c       |    4 -
 drivers/nvdimm/dimm_devs.c      |   53 +++++++++---
 drivers/nvdimm/namespace_devs.c |   14 +--
 drivers/nvdimm/nd-core.h        |   14 ++-
 drivers/nvdimm/pfn_devs.c       |    4 -
 fs/char_dev.c                   |  108 ++++++++++++++++++++++--
 include/linux/cdev.h            |   21 ++++-
 10 files changed, 238 insertions(+), 177 deletions(-)