On Fri, Jun 03, 2016 at 05:42:53AM +0100, Al Viro wrote: > On Fri, Jun 03, 2016 at 05:26:48AM +0100, Al Viro wrote: > > > Looks like the right thing to do would be to do d_drop() at no_open:, > > just before we call nfs_lookup(). If not earlier, actually... How > > about the following? > > A bit of rationale: dentry in question is negative and attempt to open > it has just failed; in case it's really negative we did that d_drop() > anyway (and then unconditionally rehashed it). In case when we proceed to > nfs_lookup() and it does not fail, we'll have it rehashed there (with the > right inode). What do we lose from doing d_drop() on *any* error here? > It's negative, with dubious validity. In the worst case, we had open > and lookup fail, but it's just us - the sucker really is negative and > somebody else would be able to revalidate it. If we drop it here (and > not rehash later), that somebody else will have to allocate an in-core > dentry before doing lookup or atomic_open. Which is negligible extra > burden.
I suspect that it got broken in commit 275bb3078 (NFSv4: Move dentry instantiation into the NFSv4-specific atomic open code). Prior to that commit, d_drop() was there (error or no error). Looks like 3.10+, indeed. I agree that we shouldn't drop it on successful open, but it needs to be done on errors. All of them, not just ENOENT, as in that commit.
