Re: [PATCH v3 04/19] VFS: use wait_var_event for waiting in d_alloc_parallel()

On Thu, 30 Apr 2026, Al Viro wrote:
> On Wed, Apr 29, 2026 at 06:26:26AM +0100, Al Viro wrote:
> 
> > with obvious adjustments in end_dir_add().  That's it.  Outside of fs/dcache.c,
> > same as in the patch you've posted, modulo renaming you've suggested for new flag.
> 
> Something like patch below (on top of -rc1, completely untested).  I've lifted
> the wakeup part out of end_dir_add() into its callers - less confusing that way.
> Note that in __d_move() the dentry you've ended up passing to end_dir_add() was
> *NOT* the one added - it was the one replaced with existing one spliced in its place.

I saw this comment the first time I read this email, but I didn't
process it properly.  That code is wrong.  It only makes sense to 
__d_wake_in_lookup_waiters() a dentry that we know was in-lookup, and in
d_move, that is target.
This can only happen (I think) in nfs where nfs_lookup() skips the lookup
for LOOKUP_RENAME_TARGET and leaves the dentry in-lookup.  Other threads
looking up that name will then block.
After the rename completes that in-lookup dentry will now be unhashed
but we need to wake it up so other threads can continue (and repeat the
lookup). 

So we need

		__d_wake_in_lookup_waiters(target);

in d_move.  target, not dentry.

Thanks for flagging this,

Also my testing has hit a problem with some sort of deadlock in the nfs
server (so accessing and XFS filesystem).  They are tring to unlink a
file and are waiting in d_alloc_parallel() under reconnect_path.
This is running generic/467.

So better hold off this patchset until I have that understood.

Thanks,
NeilBrown