From d9171b9345261e0d941d92fdda5672b5db67f968 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Fri, 15 Apr 2016 03:33:13 -0400 Subject: parallel lookups machinery, part 4 (and last) If we *do* run into an in-lookup match, we need to wait for it to cease being in-lookup. Fortunately, we do have unused space in in-lookup dentries - d_lru is never looked at until it stops being in-lookup. So we can stash a pointer to wait_queue_head from stack frame of the caller of ->lookup(). Some precautions are needed while waiting, but it's not that hard - we do hold a reference to dentry we are waiting for, so it can't go away. If it's found to be in-lookup the wait_queue_head is still alive and will remain so at least while ->d_lock is held. Moreover, the condition we are waiting for becomes true at the same point where everything on that wq gets woken up, so we can just add ourselves to the queue once. d_alloc_parallel() gets a pointer to wait_queue_head_t from its caller; lookup_slow() adjusted, d_add_ci() taught to use d_alloc_parallel() if the dentry passed to it happens to be in-lookup one (i.e. if it's been called from the parallel lookup). That's pretty much it - all that remains is to switch ->i_mutex to rwsem and have lookup_slow() take it shared. Signed-off-by: Al Viro --- fs/namei.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'fs/namei.c') diff --git a/fs/namei.c b/fs/namei.c index aa04320e1f37..7babb5e5f276 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1605,13 +1605,14 @@ static struct dentry *lookup_slow(const struct qstr *name, { struct dentry *dentry = ERR_PTR(-ENOENT), *old; struct inode *inode = dir->d_inode; + DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq); inode_lock(inode); /* Don't go there if it's already dead */ if (unlikely(IS_DEADDIR(inode))) goto out; again: - dentry = d_alloc_parallel(dir, name); + dentry = d_alloc_parallel(dir, name, &wq); if (IS_ERR(dentry)) goto out; if (unlikely(!d_in_lookup(dentry))) { -- cgit v1.2.3