From: Jan Kara jack@suse.cz
[ Upstream commit 3dc96bba65f53daa217f0a8f43edad145286a8f5 ]
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 Stable-dep-of: a44e84a9b776 ("ext4: fix deadlock due to mbcache entry corruption") Signed-off-by: Sasha Levin sashal@kernel.org --- fs/mbcache.c | 66 +++++++++++++++++++++++++++++++++++++++-- include/linux/mbcache.h | 10 ++++++- 2 files changed, 73 insertions(+), 3 deletions(-)
diff --git a/fs/mbcache.c b/fs/mbcache.c index cfc28129fb6f..2010bc80a3f2 100644 --- a/fs/mbcache.c +++ b/fs/mbcache.c @@ -11,7 +11,7 @@ /* * Mbcache is a simple key-value store. Keys need not be unique, however * key-value pairs are expected to be unique (we use this fact in - * mb_cache_entry_delete()). + * mb_cache_entry_delete_or_get()). * * Ext2 and ext4 use this cache for deduplication of extended attribute blocks. * Ext4 also uses it for deduplication of xattr values stored in inodes. @@ -125,6 +125,19 @@ void __mb_cache_entry_free(struct mb_cache_entry *entry) } EXPORT_SYMBOL(__mb_cache_entry_free);
+/* + * mb_cache_entry_wait_unused - wait to be the last user of the entry + * + * @entry - entry to work on + * + * Wait to be the last user of the entry. + */ +void mb_cache_entry_wait_unused(struct mb_cache_entry *entry) +{ + wait_var_event(&entry->e_refcnt, atomic_read(&entry->e_refcnt) <= 3); +} +EXPORT_SYMBOL(mb_cache_entry_wait_unused); + static struct mb_cache_entry *__entry_find(struct mb_cache *cache, struct mb_cache_entry *entry, u32 key) @@ -217,7 +230,7 @@ struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key, } EXPORT_SYMBOL(mb_cache_entry_get);
-/* mb_cache_entry_delete - remove a cache entry +/* mb_cache_entry_delete - try to remove a cache entry * @cache - cache we work with * @key - key * @value - value @@ -254,6 +267,55 @@ void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value) } EXPORT_SYMBOL(mb_cache_entry_delete);
+/* mb_cache_entry_delete_or_get - remove a cache entry if it has no users + * @cache - cache we work with + * @key - key + * @value - value + * + * Remove entry from cache @cache with key @key and value @value. The removal + * happens only if the entry is unused. The function returns NULL in case the + * entry was successfully removed or there's no entry in cache. Otherwise the + * function grabs reference of the entry that we failed to delete because it + * still has users and return it. + */ +struct mb_cache_entry *mb_cache_entry_delete_or_get(struct mb_cache *cache, + u32 key, u64 value) +{ + struct hlist_bl_node *node; + struct hlist_bl_head *head; + struct mb_cache_entry *entry; + + head = mb_cache_entry_head(cache, key); + hlist_bl_lock(head); + hlist_bl_for_each_entry(entry, node, head, e_hash_list) { + if (entry->e_key == key && entry->e_value == value) { + if (atomic_read(&entry->e_refcnt) > 2) { + atomic_inc(&entry->e_refcnt); + hlist_bl_unlock(head); + return entry; + } + /* We keep hash list reference to keep entry alive */ + hlist_bl_del_init(&entry->e_hash_list); + hlist_bl_unlock(head); + spin_lock(&cache->c_list_lock); + if (!list_empty(&entry->e_list)) { + list_del_init(&entry->e_list); + if (!WARN_ONCE(cache->c_entry_count == 0, + "mbcache: attempt to decrement c_entry_count past zero")) + cache->c_entry_count--; + atomic_dec(&entry->e_refcnt); + } + spin_unlock(&cache->c_list_lock); + mb_cache_entry_put(cache, entry); + return NULL; + } + } + hlist_bl_unlock(head); + + return NULL; +} +EXPORT_SYMBOL(mb_cache_entry_delete_or_get); + /* mb_cache_entry_touch - cache entry got used * @cache - cache the entry belongs to * @entry - entry that got used 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);