diff options
| author | Hao Li <lihao2018.fnst@cn.fujitsu.com> | 2020-12-08 10:10:50 +0800 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2020-12-10 17:33:17 -0500 |
| commit | 77573fa310d95e4293efdec98dace74cd9e52f43 (patch) | |
| tree | a7a12a6a10ef23409c6d213179d5ac3afad8d6ae /fs/dcache.c | |
| parent | 88149082bb8ef31b289673669e080ec6a00c2e59 (diff) | |
| download | linux-77573fa310d95e4293efdec98dace74cd9e52f43.tar.bz2 | |
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>
Diffstat (limited to 'fs/dcache.c')
| -rw-r--r-- | fs/dcache.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index ea0485861d93..97e81a844a96 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry) * a reference to the dentry and change that, but * our work is done - we can leave the dentry * around with a zero refcount. + * + * Nevertheless, there are two cases that we should kill + * the dentry anyway. + * 1. free disconnected dentries as soon as their refcount + * reached zero. + * 2. free dentries if they should not be cached. */ smp_rmb(); d_flags = READ_ONCE(dentry->d_flags); - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | + DCACHE_DISCONNECTED | DCACHE_DONTCACHE; /* Nothing to do? Dropping the reference was all we needed? */ if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) |