fix idiotic braino in d_alloc_parallel()
Check for d_unhashed() while searching in in-lookup hash was absolutely
wrong. Worse, it masked a deadlock on dget() done under bitlock that
nests inside ->d_lock. Thanks to J. R. Okajima for spotting it.
Spotted-by: "J. R. Okajima" <hooanon05g@gmail.com>
Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/dcache.c b/fs/dcache.c
index b7eddfd..d6847d7 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2503,7 +2503,6 @@
rcu_read_unlock();
goto retry;
}
- rcu_read_unlock();
/*
* No changes for the parent since the beginning of d_lookup().
* Since all removals from the chain happen with hlist_bl_lock(),
@@ -2516,8 +2515,6 @@
continue;
if (dentry->d_parent != parent)
continue;
- if (d_unhashed(dentry))
- continue;
if (parent->d_flags & DCACHE_OP_COMPARE) {
int tlen = dentry->d_name.len;
const char *tname = dentry->d_name.name;
@@ -2529,9 +2526,18 @@
if (dentry_cmp(dentry, str, len))
continue;
}
- dget(dentry);
hlist_bl_unlock(b);
- /* somebody is doing lookup for it right now; wait for it */
+ /* now we can try to grab a reference */
+ if (!lockref_get_not_dead(&dentry->d_lockref)) {
+ rcu_read_unlock();
+ goto retry;
+ }
+
+ rcu_read_unlock();
+ /*
+ * somebody is likely to be still doing lookup for it;
+ * wait for them to finish
+ */
spin_lock(&dentry->d_lock);
d_wait_lookup(dentry);
/*
@@ -2562,6 +2568,7 @@
dput(new);
return dentry;
}
+ rcu_read_unlock();
/* we can't take ->d_lock here; it's OK, though. */
new->d_flags |= DCACHE_PAR_LOOKUP;
new->d_wait = wq;