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VFS: Impose ordering on accesses of d_inode and d_flags

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Impose ordering on accesses of d_inode and d_flags to avoid the need to do
this:

	if (!dentry->d_inode || d_is_negative(dentry)) {

when this:

	if (d_is_negative(dentry)) {

should suffice.

This check is especially problematic if a dentry can have its type field set
to something other than DENTRY_MISS_TYPE when d_inode is NULL (as in
unionmount).

What we really need to do is stick a write barrier between setting d_inode and
setting d_flags and a read barrier between reading d_flags and reading
d_inode.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
David Howells
2015-03-05 14:09:22 +00:00
committed by Al Viro
parent 525d27b235
commit 4bf46a2726
2 changed files with 42 additions and 26 deletions
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21
include/linux/dcache.h
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@@ -404,26 +404,11 @@ static inline bool d_mountpoint(const struct dentry *dentry)
/*
* Directory cache entry type accessor functions.
*/
static inline void __d_set_type(struct dentry *dentry, unsigned type)
{
dentry->d_flags = (dentry->d_flags & ~DCACHE_ENTRY_TYPE) | type;
}
static inline void __d_clear_type(struct dentry *dentry)
{
__d_set_type(dentry, DCACHE_MISS_TYPE);
}
static inline void d_set_type(struct dentry *dentry, unsigned type)
{
spin_lock(&dentry->d_lock);
__d_set_type(dentry, type);
spin_unlock(&dentry->d_lock);
}
static inline unsigned __d_entry_type(const struct dentry *dentry)
{
return dentry->d_flags & DCACHE_ENTRY_TYPE;
unsigned type = READ_ONCE(dentry->d_flags);
smp_rmb();
return type & DCACHE_ENTRY_TYPE;
}
static inline bool d_is_miss(const struct dentry *dentry)