ext4: protect pa->pa_free in ext4_discard_allocated_blocks

If ext4_mb_mark_diskspace_used fails in ext4_mb_new_blocks, we may
discard pa already in list. Protect pa with pa_lock to avoid race.
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20230303172120.3800725-7-shikemeng@huaweicloud.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -4267,8 +4267,11 @@ static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
 		ext4_mb_unload_buddy(&e4b);
 		return;
 	}
-	if (pa->pa_type == MB_INODE_PA)
+	if (pa->pa_type == MB_INODE_PA) {
+		spin_lock(&pa->pa_lock);
 		pa->pa_free += ac->ac_b_ex.fe_len;
+		spin_unlock(&pa->pa_lock);
+	}
 }
 
 /*