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Hao Li 77573fa310 fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set
If DCACHE_REFERENCED is set, fast_dput() will return true, and then
retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result,
the dentry won't be killed and the corresponding inode can't be evicted.
In the following example, the DAX policy can't take effects unless we
do a drop_caches manually.

  # DCACHE_LRU_LIST will be set
  echo abcdefg > test.txt

  # DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything
  xfs_io -c 'chattr +x' test.txt

  # Drop caches to make DAX changing take effects
  echo 2 > /proc/sys/vm/drop_caches

What this patch does is preventing fast_dput() from returning true if
DCACHE_DONTCACHE is set. Then retain_dentry() will detect the
DCACHE_DONTCACHE and will return false. As a result, the dentry will be
killed and the inode will be evicted. In this way, if we change per-file
DAX policy, it will take effects automatically after this file is closed
by all processes.

I also add some comments to make the code more clear.

Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-12-10 17:33:17 -05:00
arch Yet two more places which invoke tracing from RCU disabled regions in the 2020-11-29 11:19:26 -08:00
block
certs
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Documentation Kbuild fixes for v5.10 2020-11-28 10:42:30 -08:00
drivers Yet two more places which invoke tracing from RCU disabled regions in the 2020-11-29 11:19:26 -08:00
fs fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set 2020-12-10 17:33:17 -05:00
include fs: Handle I_DONTCACHE in iput_final() instead of generic_drop_inode() 2020-12-10 17:33:17 -05:00
init Urgent printk fix for 5.10 2020-11-27 10:38:36 -08:00
ipc
kernel Yet two more places which invoke tracing from RCU disabled regions in the 2020-11-29 11:19:26 -08:00
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mm mm: fix VM_BUG_ON(PageTail) and BUG_ON(PageWriteback) 2020-11-24 15:23:19 -08:00
net linux-can-fixes-for-5.10-20201127 2020-11-27 11:13:39 -08:00
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scripts Kbuild fixes for v5.10 2020-11-28 10:42:30 -08:00
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tools perf probe: Change function definition check due to broken DWARF 2020-11-27 14:36:15 -03:00
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.mailmap ARM: 2020-11-27 11:04:13 -08:00
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MAINTAINERS Char/misc driver fixes for 5.10-rc6 2020-11-28 10:04:36 -08:00
Makefile Linux 5.10-rc6 2020-11-29 15:50:50 -08:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.