mbcache: add functions to delete entry if unused

Add function mb_cache_entry_delete_or_get() to delete mbcache entry if
it is unused and also add a function to wait for entry to become unused
- mb_cache_entry_wait_unused(). We do not share code between the two
deleting function as one of them will go away soon.

CC: stable@vger.kernel.org
Fixes: 82939d7999df ("ext4: convert to mbcache2")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220712105436.32204-2-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 9 insertions, 1 deletions

diff --git a/include/linux/mbcache.h b/include/linux/mbcache.h
index 20f1e3ff6013..8eca7f25c432 100644
--- a/include/linux/mbcache.h
+++ b/include/linux/mbcache.h
@@ -30,15 +30,23 @@ void mb_cache_destroy(struct mb_cache *cache);
 int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
 			  u64 value, bool reusable);
 void __mb_cache_entry_free(struct mb_cache_entry *entry);
+void mb_cache_entry_wait_unused(struct mb_cache_entry *entry);
 static inline int mb_cache_entry_put(struct mb_cache *cache,
 				     struct mb_cache_entry *entry)
 {
-	if (!atomic_dec_and_test(&entry->e_refcnt))
+	unsigned int cnt = atomic_dec_return(&entry->e_refcnt);
+
+	if (cnt > 0) {
+		if (cnt <= 3)
+			wake_up_var(&entry->e_refcnt);
 		return 0;
+	}
 	__mb_cache_entry_free(entry);
 	return 1;
 }
 
+struct mb_cache_entry *mb_cache_entry_delete_or_get(struct mb_cache *cache,
+						    u32 key, u64 value);
 void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value);
 struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
 					  u64 value);