On Wed, Jul 20, 2022 at 07:00:32PM +0800, Hillf Danton wrote: > To help debug it, de-union d_in_lookup_hash with d_alias and add debug > info after dentry is killed. If any warning hits, we know where to add > something like > > WARN_ON(dentry->d_flags & DCACHE_DENTRY_KILLED); > > before hlist_bl_add or hlist_add. IDGI. That clearly has nothing to do with in-lookup stuff - no DCACHE_PAR_LOOKUP in reported flags, so it either never had it set, or it went through __d_lookup_done() already. If anything, it might have already been through d_free(), with d_rcu being confused for d_alias. I'd do something like WARN_ON(dentry->d_flags & (1U<<31)); dentry->d_flags |= 1U << 31; in the begining of d_free() (possibly with dumping dentry state if we hit that, not that there would be much to report; d_name.name might be informative, though). Again, in-lookup looks like a red herring - DCACHE_PAR_LOOKUP is set only in d_alloc_parallel(), right next to the insertion into the list and removed only in __d_lookup_free(), right next to the removal from the same. No DCACHE_PAR_LOOKUP in ->d_flags (it's 0x8008 in reported cases, i.e. DCACHE_OP_REVALIDATE | DCACHE_DENTRY_KILLED). What's more, take a look at retain_dentry(); WARN_ON(d_in_lookup(dentry)) right at the top and it had not triggered in any of the reports I've seen in that thread. Granted, it's not called on each path to __dentry_kill(), but it is on the call chains I've seen reported... Another thing that might be interesting to know is ->d_sb, along with ->d_sb->s_type->name and ->d_sb->s_id. That should tell which fs it's on... I wonder if anyone had seen anything similar outside of parisc... I don't know if I have any chance to reproduce it here - the only parisc box I've got is a 715/100 (assuming the disk is still alive) and it's 32bit, unlike the reported setups and, er, not fast. qemu seems to have some parisc support, but it's 32bit-only at the moment... PS: please, Cc fsdevel on anything VFS-related. Very few people are still subscribed to l-k these days - I am, but it's impossible to read through and postings can easily get missed.
