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fs: use RCU read side protection in d_validate 

d_validate does a purely read lookup in the dentry hash, so use RCU read side
locking instead of dcache_lock.  Split out from a larget patch by
Nick Piggin <npiggin@suse.de>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Christoph Hellwig 2010-10-10 05:36:27 -04:00 committed by Al Viro
parent a4633357ac
commit 3825bdb7ed
1 changed files with 12 additions and 19 deletions
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31
fs/dcache.c
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@ -1491,33 +1491,26 @@ out:
* This is used by ncpfs in its readdir implementation.
* Zero is returned in the dentry is invalid.
*/
int d_validate(struct dentry *dentry, struct dentry *dparent)
int d_validate(struct dentry *dentry, struct dentry *parent)
{
struct hlist_head *base;
struct hlist_node *lhp;
struct hlist_head *head = d_hash(parent, dentry->d_name.hash);
struct hlist_node *node;
struct dentry *d;
/* Check whether the ptr might be valid at all.. */
if (!kmem_ptr_validate(dentry_cache, dentry))
goto out;
return 0;
if (dentry->d_parent != parent)
return 0;
if (dentry->d_parent != dparent)
goto out;
spin_lock(&dcache_lock);
base = d_hash(dparent, dentry->d_name.hash);
hlist_for_each(lhp,base) {
/* hlist_for_each_entry_rcu() not required for d_hash list
* as it is parsed under dcache_lock
*/
if (dentry == hlist_entry(lhp, struct dentry, d_hash)) {
__dget_locked(dentry);
spin_unlock(&dcache_lock);
rcu_read_lock();
hlist_for_each_entry_rcu(d, node, head, d_hash) {
if (d == dentry) {
dget(dentry);
return 1;
}
}
spin_unlock(&dcache_lock);
out:
rcu_read_unlock();
return 0;
}
EXPORT_SYMBOL(d_validate);