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

From: Nicolai Stange
Date: Wed May 03 2017 - 10:17:52 EST

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.



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

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

[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(-)