ext4: Refactor code related to freeing PAs

This patch makes the following changes:

*  Rename ext4_mb_pa_free to ext4_mb_pa_put_free
   to better reflect its purpose

*  Add new ext4_mb_pa_free() which only handles freeing

*  Refactor ext4_mb_pa_callback() to use ext4_mb_pa_free()

There are no functional changes in this patch

Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/b273bc9cbf5bd278f641fa5bc6c0cc9e6cb3330c.1679731817.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -4528,16 +4528,22 @@ static void ext4_mb_mark_pa_deleted(struct super_block *sb,
 	}
 }
 
-static void ext4_mb_pa_callback(struct rcu_head *head)
+static inline void ext4_mb_pa_free(struct ext4_prealloc_space *pa)
 {
-	struct ext4_prealloc_space *pa;
-	pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
-
+	BUG_ON(!pa);
 	BUG_ON(atomic_read(&pa->pa_count));
 	BUG_ON(pa->pa_deleted == 0);
 	kmem_cache_free(ext4_pspace_cachep, pa);
 }
 
+static void ext4_mb_pa_callback(struct rcu_head *head)
+{
+	struct ext4_prealloc_space *pa;
+
+	pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
+	ext4_mb_pa_free(pa);
+}
+
 /*
  * drops a reference to preallocated space descriptor
  * if this was the last reference and the space is consumed
@@ -5055,14 +5061,20 @@ static int ext4_mb_pa_alloc(struct ext4_allocation_context *ac)
 	return 0;
 }
 
-static void ext4_mb_pa_free(struct ext4_allocation_context *ac)
+static void ext4_mb_pa_put_free(struct ext4_allocation_context *ac)
 {
 	struct ext4_prealloc_space *pa = ac->ac_pa;
 
 	BUG_ON(!pa);
 	ac->ac_pa = NULL;
 	WARN_ON(!atomic_dec_and_test(&pa->pa_count));
-	kmem_cache_free(ext4_pspace_cachep, pa);
+	/*
+	 * current function is only called due to an error or due to
+	 * len of found blocks < len of requested blocks hence the PA has not
+	 * been added to grp->bb_prealloc_list. So we don't need to lock it
+	 */
+	pa->pa_deleted = 1;
+	ext4_mb_pa_free(pa);
 }
 
 #ifdef CONFIG_EXT4_DEBUG
@@ -5605,13 +5617,13 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
 		 * So we have to free this pa here itself.
 		 */
 		if (*errp) {
-			ext4_mb_pa_free(ac);
+			ext4_mb_pa_put_free(ac);
 			ext4_discard_allocated_blocks(ac);
 			goto errout;
 		}
 		if (ac->ac_status == AC_STATUS_FOUND &&
 			ac->ac_o_ex.fe_len >= ac->ac_f_ex.fe_len)
-			ext4_mb_pa_free(ac);
+			ext4_mb_pa_put_free(ac);
 	}
 	if (likely(ac->ac_status == AC_STATUS_FOUND)) {
 		*errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
@@ -5630,7 +5642,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
 		 * If block allocation fails then the pa allocated above
 		 * needs to be freed here itself.
 		 */
-		ext4_mb_pa_free(ac);
+		ext4_mb_pa_put_free(ac);
 		*errp = -ENOSPC;
 	}