ext4: Move overlap assert logic into a separate function

Abstract out the logic to double check for overlaps in normalize_pa to
a separate function. Since there has been no reports in past where we
have seen any overlaps which hits this bug_on(), in future we can
consider calling this function under "#ifdef AGGRESSIVE_CHECK" only.

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/35dd5d94fa0b2d1cd2d2947adf8967279c72967d.1679731817.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -3978,6 +3978,29 @@ static void ext4_mb_normalize_group_request(struct ext4_allocation_context *ac)
 	mb_debug(sb, "goal %u blocks for locality group\n", ac->ac_g_ex.fe_len);
 }
 
+static inline void
+ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
+			  ext4_lblk_t start, ext4_lblk_t end)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
+	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
+	struct ext4_prealloc_space *tmp_pa;
+	ext4_lblk_t tmp_pa_start, tmp_pa_end;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
+		spin_lock(&tmp_pa->pa_lock);
+		if (tmp_pa->pa_deleted == 0) {
+			tmp_pa_start = tmp_pa->pa_lstart;
+			tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
+
+			BUG_ON(!(start >= tmp_pa_end || end <= tmp_pa_start));
+		}
+		spin_unlock(&tmp_pa->pa_lock);
+	}
+	rcu_read_unlock();
+}
+
 /*
  * Normalization means making request better in terms of
  * size and alignment
@@ -4135,17 +4158,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 	size = end - start;
 
 	/* XXX: extra loop to check we really don't overlap preallocations */
-	rcu_read_lock();
-	list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
-		spin_lock(&tmp_pa->pa_lock);
-		if (tmp_pa->pa_deleted == 0) {
-			tmp_pa_start = tmp_pa->pa_lstart;
-			tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
-			BUG_ON(!(start >= tmp_pa_end || end <= tmp_pa_start));
-		}
-		spin_unlock(&tmp_pa->pa_lock);
-	}
-	rcu_read_unlock();
+	ext4_mb_pa_assert_overlap(ac, start, end);
 
 	/*
 	 * In this function "start" and "size" are normalized for better