beginning of transition to parallel lookups - marking in-lookup dentries
marked as such when (would be) parallel lookup is about to pass them
to actual ->lookup(); unmarked when
* __d_add() is about to make it hashed, positive or not.
* __d_move() (from d_splice_alias(), directly or via
__d_unalias()) puts a preexisting dentry in its place
* in caller of ->lookup() if it has escaped all of the
above. Bug (WARN_ON, actually) if it reaches the final dput()
or d_instantiate() while still marked such.
As the result, we are guaranteed that for as long as the flag is
set, dentry will
* remain negative unhashed with positive refcount
* never have its ->d_alias looked at
* never have its ->d_lru looked at
* never have its ->d_parent and ->d_name changed
Right now we have at most one such for any given parent directory.
With parallel lookups that restriction will weaken to
* only exist when parent is locked shared
* at most one with given (parent,name) pair (comparison of
names is according to ->d_compare())
* only exist when there's no hashed dentry with the same
(parent,name)
Transition will take the next several commits; unfortunately, we'll
only be able to switch to rwsem at the end of this series. The
reason for not making it a single patch is to simplify review.
New primitives: d_in_lookup() (a predicate checking if dentry is in
the in-lookup state) and d_lookup_done() (tells the system that
we are done with lookup and if it's still marked as in-lookup, it
should cease to be such).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/dcache.c b/fs/dcache.c
index 20394fb..0f1d938 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -761,6 +761,8 @@
/* Slow case: now with the dentry lock held */
rcu_read_unlock();
+ WARN_ON(d_in_lookup(dentry));
+
/* Unreachable? Get rid of it */
if (unlikely(d_unhashed(dentry)))
goto kill_it;
@@ -1746,6 +1748,7 @@
static void __d_instantiate(struct dentry *dentry, struct inode *inode)
{
unsigned add_flags = d_flags_for_inode(inode);
+ WARN_ON(d_in_lookup(dentry));
spin_lock(&dentry->d_lock);
hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
@@ -2361,12 +2364,20 @@
}
EXPORT_SYMBOL(d_rehash);
+void __d_lookup_done(struct dentry *dentry)
+{
+ dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
+ /* more stuff will land here */
+}
+EXPORT_SYMBOL(__d_lookup_done);
/* inode->i_lock held if inode is non-NULL */
static inline void __d_add(struct dentry *dentry, struct inode *inode)
{
spin_lock(&dentry->d_lock);
+ if (unlikely(d_in_lookup(dentry)))
+ __d_lookup_done(dentry);
if (inode) {
unsigned add_flags = d_flags_for_inode(inode);
hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
@@ -2612,6 +2623,8 @@
BUG_ON(d_ancestor(target, dentry));
dentry_lock_for_move(dentry, target);
+ if (unlikely(d_in_lookup(target)))
+ __d_lookup_done(target);
write_seqcount_begin(&dentry->d_seq);
write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);