From 85c7f81041d57cfe9dc97f4680d5586b54534a39 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Thu, 14 Apr 2016 19:52:13 -0400 Subject: 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 --- fs/namei.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'fs/namei.c') diff --git a/fs/namei.c b/fs/namei.c index c275635c4b9e..26e5f84e0c36 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1634,7 +1634,11 @@ static struct dentry *lookup_slow(const struct qstr *name, inode_unlock(inode); return ERR_PTR(-ENOMEM); } + spin_lock(&dentry->d_lock); + dentry->d_flags |= DCACHE_PAR_LOOKUP; + spin_unlock(&dentry->d_lock); old = inode->i_op->lookup(inode, dentry, flags); + d_lookup_done(dentry); if (unlikely(old)) { dput(dentry); dentry = old; -- cgit v1.2.3-70-g09d2