dcache: add extra sanity checks of the dentry in dentry_free()

If d_flags isn't what we expect, then it's good to display it. Add a new
DENTRY_WARN_ONCE() macro that also displays d_flags for the dentry.
Change D_FLAG_VERIFY() to call that instead of a generic WARN_ON_ONCE().

Change the existing hlist_unhashed() check in dentry_free() to use the
new macro, and add checks for other invariants of a dead dentry. Notably:

1) Ensure that DCACHE_LRU_LIST and DCACHE_SHRINK_LIST are not set.

2) Ensure that d_lockref is negative

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260422-dcache-warn-v1-1-50155e1b40b6@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

diff --git a/fs/dcache.c b/fs/dcache.c
index 8ffc4ef79bbab132fdf9ec91385dd22156b858c2..131a3cf1c360990483020a4e8d99ea9076188ac3 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -426,9 +426,16 @@ static inline void __d_clear_type_and_inode(struct dentry *dentry)
                this_cpu_inc(nr_dentry_negative);
 }
 
+#define DENTRY_WARN_ONCE(condition, dentry) \
+       WARN_ONCE((condition), "dentry=%p d_flags=0x%x\n", (dentry), (dentry)->d_flags)
+#define D_FLAG_VERIFY(dentry, x) \
+       DENTRY_WARN_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x), (dentry))
+
 static void dentry_free(struct dentry *dentry)
 {
-       WARN_ON(d_really_is_positive(dentry));
+       DENTRY_WARN_ONCE(d_really_is_positive(dentry), dentry);
+       DENTRY_WARN_ONCE(dentry->d_lockref.count >= 0, dentry);
+       D_FLAG_VERIFY(dentry, 0);
        if (unlikely(dname_external(dentry))) {
                struct external_name *p = external_name(dentry);
                if (likely(atomic_dec_and_test(&p->count))) {
@@ -495,7 +502,6 @@ static void dentry_unlink_inode(struct dentry * dentry)
  * These helper functions make sure we always follow the
  * rules. d_lock must be held by the caller.
  */
-#define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
 static void d_lru_add(struct dentry *dentry)
 {
        D_FLAG_VERIFY(dentry, 0);