Shreeya Patel <shreeya.patel@xxxxxxxxxxxxx> writes: > 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. > > Signed-off-by: Shreeya Patel <shreeya.patel@xxxxxxxxxxxxx> > --- > fs/dcache.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index cf871a81f4fd..2a28ab64a165 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -2565,6 +2565,15 @@ static void d_wait_lookup(struct dentry *dentry) > } > } > > +static inline bool d_same_exact_name(const struct dentry *dentry, > + const struct dentry *parent, > + const struct qstr *name) > +{ > + if (dentry->d_name.len != name->len) > + return false; > + return dentry_cmp(dentry, name->name, name->len) == 0; > +} I don't like the idea of having a flavor of a dentry comparison function that doesn't invoke d_compare. In particular because d_compare might be used for all sorts of things, and this fix is really specific to the case-insensitive case. Would it be possible to fold this change into generic_ci_d_compare? If we could flag the dentry as part of a parallel lookup under the relevant condition, generic_ci_d_compare could simply return immediately in such case. > + > struct dentry *d_alloc_parallel(struct dentry *parent, > const struct qstr *name, > wait_queue_head_t *wq) > @@ -2575,6 +2584,7 @@ struct dentry *d_alloc_parallel(struct dentry *parent, > struct dentry *new = d_alloc(parent, name); > struct dentry *dentry; > unsigned seq, r_seq, d_seq; > + int ci_dir = IS_CASEFOLDED(parent->d_inode); > > if (unlikely(!new)) > return ERR_PTR(-ENOMEM); > @@ -2626,8 +2636,14 @@ struct dentry *d_alloc_parallel(struct dentry *parent, > continue; > if (dentry->d_parent != parent) > continue; > - if (!d_same_name(dentry, parent, name)) > - continue; > + if (ci_dir) { > + if (!d_same_exact_name(dentry, parent, name)) > + continue; > + } else { As is, this is problematic because d_alloc_parallel is also part of the lookup path (see lookup_open, lookup_slow). In those cases, you want to do the CI comparison, to prevent racing two tasks creating a dentry differing only by case. > + if (!d_same_name(dentry, parent, name)) > + continue; > + } > + > hlist_bl_unlock(b); > /* now we can try to grab a reference */ > if (!lockref_get_not_dead(&dentry->d_lockref)) { -- Gabriel Krisman Bertazi