On Wed, Sep 29, 2021 at 04:23:38PM +0530, Shreeya Patel wrote:

There is a soft hang caused by a deadlock in d_alloc_parallel which
waits up on lookups to finish for the dentries in the parent directory's
hash_table.
In case when d_add_ci is called from the fs layer's lookup functions,
the dentry being looked up is already in the hash table (created before
the fs lookup function gets called). We should not be processing the
same dentry that is being looked up, hence, in case of case-insensitive
filesystems we are making it a case-exact match to prevent this from
happening.

NAK.  What you are doing would lead to parallel calls of ->lookup() in the
same directory for names that would compare as equal.  Which violates
all kinds of assumptions in the analysis of dentry tree locking.

d_add_ci() is used to force the "exact" spelling of the name on lookup -
that's the whole point of that thing.  What are you trying to achieve,
and what's the point of mixing that with non-trivial ->d_compare()?

If it's "force to exact spelling on lookup, avoid calling ->lookup() on
aliases", d_add_ci() is simply not a good match.