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Subject[PATCH 01/11] fs/dcache: Fix incorrect accounting of negative dentries
Date
The nr_dentry_negative counter only tracks the number of negative
dentries in lru lists, not when they are in shrink lists. In
both __d_clear_type_and_inode() and __d_instantiate(), only the
DCACHE_LRU_LIST flag is checked. Though it is highly unlikely that
the DCACHE_SHRINK_LIST flag may be set, it is still possible. Fix that
by checking the DCACHE_SHRINK_LIST flag as well to make sure that the
accounting is correct.

The negative dentry test is also moved from __d_instantiate() to
__d_set_inode_and_type() to cover more cases.

Fixes: af0c9af1b3f6 ("fs/dcache: Track & report number of negative dentries")

Signed-off-by: Waiman Long <longman@redhat.com>
---
fs/dcache.c | 13 +++++++------
include/linux/dcache.h | 9 +++++++++
2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index b280e07e162b..c17b538bf41c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -315,6 +315,12 @@ static inline void __d_set_inode_and_type(struct dentry *dentry,
{
unsigned flags;

+ /*
+ * Decrement negative dentry count if it was in the LRU list.
+ */
+ if (unlikely(d_in_lru(dentry) && d_is_negative(dentry)))
+ this_cpu_dec(nr_dentry_negative);
+
dentry->d_inode = inode;
flags = READ_ONCE(dentry->d_flags);
flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
@@ -329,7 +335,7 @@ static inline void __d_clear_type_and_inode(struct dentry *dentry)
flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
WRITE_ONCE(dentry->d_flags, flags);
dentry->d_inode = NULL;
- if (dentry->d_flags & DCACHE_LRU_LIST)
+ if (d_in_lru(dentry))
this_cpu_inc(nr_dentry_negative);
}

@@ -1919,11 +1925,6 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode)
WARN_ON(d_in_lookup(dentry));

spin_lock(&dentry->d_lock);
- /*
- * Decrement negative dentry count if it was in the LRU list.
- */
- if (dentry->d_flags & DCACHE_LRU_LIST)
- this_cpu_dec(nr_dentry_negative);
hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
raw_write_seqcount_begin(&dentry->d_seq);
__d_set_inode_and_type(dentry, inode, add_flags);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index c1488cc84fd9..2762ca2508f9 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -369,6 +369,15 @@ static inline void d_lookup_done(struct dentry *dentry)
}
}

+/*
+ * Dentry is in a LRU list, not a shrink list.
+ */
+static inline bool d_in_lru(struct dentry *dentry)
+{
+ return (dentry->d_flags & (DCACHE_SHRINK_LIST | DCACHE_LRU_LIST))
+ == DCACHE_LRU_LIST;
+}
+
extern void dput(struct dentry *);

static inline bool d_managed(const struct dentry *dentry)
--
2.18.1
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