linux-kernel - [RFC PATCH v2 0/9] debugfs: per-file removal protection

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Date:   Wed,  3 May 2017 16:17:17 +0200
From:   Nicolai Stange <nicstange@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Johannes Berg <johannes@...solutions.net>,
        "Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Nicolai Stange <nicstange@...il.com>
Subject: [RFC PATCH v2 0/9] debugfs: per-file removal protection

Hello Greg,

this is the second attempt to implement debugfs file removal protection
at file granularity. The first one can be found at [1].

Note that I left out the IB/hfi1 people from the get_maintainer list and
thus, sent this in RFC mode only because the following still needs to get
sorted out:
1. It's still not clear whether something like [9/9] ("debugfs: free
   debugfs_fsdata instances") is actually wanted. Your advice welcome!

2. The kernel test robot complained about [2/9] ("debugfs: defer
   debugfs_fsdata allocation to first usage") in v1. Despite Xiaolong's
   support, I wasn't able to reproduce this, but I hope that the changes
   mentioned below resolve it now. We'll see.

Thanks,

Nicolai

[1] http://lkml.kernel.org/r/20170416095137.2784-1-nicstange@gmail.com

Changes to v1:

  [2/9] ("debugfs: implement per-file removal protection")
  - In an attempt to resolve the issue reported by the kernel test robot
    for v1, restrict the "extended removal logic" to regular files in
    __debugfs_remove().

  [8/9] ("debugfs: defer debugfs_fsdata allocation to first usage")
  - Following review from Johannes Berg, replace the WARN_ON in
    debugfs_real_fops() by a WARN + 'return NULL'. The return NULL is
    expected to crash current soon and serves as an alternative for a
    BUG_ON here.
  - Mention the change in debugfs_real_fops() in the commit message.

  [9/9] ("debugfs: free debugfs_fsdata instances")
  - Following advice from Paul E. McKenney, make debugfs_file_get()
    release the RCU read section inbetween retry loop iterations.
  - Fix a race in debugfs_file_get()'s path handling a concurrent
    debugfs_file_put(): the former must not "help out resetting ->d_fsdata"
    because this can wipe out another debugfs_file_get()'s achievements.

Nicolai Stange (9):
  debugfs: add support for more elaborate ->d_fsdata
  debugfs: implement per-file removal protection
  debugfs: debugfs_real_fops(): drop __must_hold sparse annotation
  debugfs: convert to debugfs_file_get() and -put()
  IB/hfi1: convert to debugfs_file_get() and -put()
  debugfs: purge obsolete SRCU based removal protection
  debugfs: call debugfs_real_fops() only after debugfs_file_get()
  debugfs: defer debugfs_fsdata allocation to first usage
  debugfs: free debugfs_fsdata instances

 drivers/infiniband/hw/hfi1/debugfs.c |  20 +--
 fs/debugfs/file.c                    | 278 ++++++++++++++++++++++++-----------
 fs/debugfs/inode.c                   |  60 ++++++--
 fs/debugfs/internal.h                |  15 ++
 include/linux/debugfs.h              |  33 +----
 lib/Kconfig.debug                    |   1 -
 6 files changed, 266 insertions(+), 141 deletions(-)

-- 
2.12.2