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Subject[RFC PATCH 0/9] debugfs: per-file removal protection
Hello Greg,

this series implements the debugfs removal protection at file granularity,
meant to solve the livelock issue reported by Johannes [1]:

Task 1 Task 2
debugfs_use_file_start(&d2, ...);
debugfs_remove(d1); mutex_lock(&m);

with d1 != d2.

In order to be able to store the additionally required per-dentry state,
a small container struct, debugfs_fsdata, will be allocated and installed
at ->d_fsdata.

The remaining question is if and how these debugfs_fsdata instances should
be freed. For one possible solution, please see
[9/9] ("debugfs: free debugfs_fsdata instances"). As stated in that patch's
description, I'm not convinced that it's a particularly good one -- it's
included only to show how a lock-free/RCU based scheme would look like.
In order to avoid frequent allocations and deallocations, I'd personally
not free the debugfs_fsdata instances at all: there would be exactly one
per debugfs file ever opened, which probably isn't too much. If you don't
agree, I can try and see how a simpler solution based on a global spinlock
would look like... Any advice on how to proceed with this welcome!




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 | 272 +++++++++++++++++++++++------------
fs/debugfs/inode.c | 55 +++++--
fs/debugfs/internal.h | 15 ++
include/linux/debugfs.h | 33 +----
lib/Kconfig.debug | 1 -
6 files changed, 256 insertions(+), 140 deletions(-)


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