alinux: hotfix: Add Cloud Kernel hotfix enhancement

We reserve some fields beforehand for core structures prone to change,
so that we won't hurt when extra fields have to be added for hotfix,
thereby inceasing the success rate, we even can hot add features with
this enhancement.

After reserving, normally cache does not matter as the reserved fields
(usually at tail) are not accessed at all.

Currently involve the following structures:
    MM:
    struct zone
    struct pglist_data
    struct mm_struct
    struct vm_area_struct
    struct mem_cgroup
    struct writeback_control

    Block:
    struct gendisk
    struct backing_dev_info
    struct bio
    struct queue_limits
    struct request_queue
    struct blkcg
    struct blkcg_policy
    struct blk_mq_hw_ctx
    struct blk_mq_tag_set
    struct blk_mq_queue_data
    struct blk_mq_ops
    struct elevator_mq_ops
    struct inode
    struct dentry
    struct address_space
    struct block_device
    struct hd_struct
    struct bio_set

    Network:
    struct sk_buff
    struct sock
    struct net_device_ops
    struct xt_target
    struct dst_entry
    struct dst_ops
    struct fib_rule

    Scheduler:
    struct task_struct
    struct cfs_rq
    struct rq
    struct sched_statistics
    struct sched_entity
    struct signal_struct
    struct task_group
    struct cpuacct

    cgroup:
    struct cgroup_root
    struct cgroup_subsys_state
    struct cgroup_subsys
    struct css_set

Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
[ caspar: use SPDX-License-Identifier ]
Signed-off-by: Caspar Zhang <caspar@linux.alibaba.com>

Author: Xunlei Pang

include/linux/ali_hotfix.h

@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (c) 2019 Xunlei Pang <xlpang@linux.alibaba.com>
+ */
+
+#ifndef _LINUX_ALI_HOTFIX_H
+#define _LINUX_ALI_HOTFIX_H
+
+#include <linux/compiler.h>
+
+/*
+ * ALI_HOTFIX_RESERVE* - reserve fields for core structures prone to change
+ * ALI_HOTFIX_USE*     - use the reserved field in your hotfix
+ * ALI_HOTFIX_REPLACE  - replacement of _orig with a union of _orig and _new
+ */
+
+#define _ALI_HOTFIX_REPLACE(_orig, _new)		\
+	union {						\
+		_new;					\
+		struct {				\
+			_orig;				\
+		} __UNIQUE_ID(ali_hotfix_hide);		\
+	}
+
+#define ALI_HOTFIX_REPLACE(_orig, _new)	_ALI_HOTFIX_REPLACE(_orig, _new);
+
+/*
+ * We tried to standardize on alikernel reserved names.  These wrappers leverage
+ * those common names making it easier to read and find in the code.
+ */
+#define _ALI_HOTFIX_RESERVE(n)		unsigned long ali_reserved##n
+#define _ALI_HOTFIX_RESERVE_P(n)	void (*ali_reserved##n)(void)
+
+#define ALI_HOTFIX_RESERVE(n)		_ALI_HOTFIX_RESERVE(n);
+#define ALI_HOTFIX_RESERVE_P(n)		_ALI_HOTFIX_RESERVE_P(n);
+
+/*
+ * Wrappers to replace standard alikernel reserved elements.
+ */
+#define ALI_HOTFIX_USE(n, _new)				\
+	ALI_HOTFIX_REPLACE(_ALI_HOTFIX_RESERVE(n), _new)
+#define ALI_HOTFIX_USE_P(n, _new)			\
+	ALI_HOTFIX_REPLACE(_ALI_HOTFIX_RESERVE_P(n), _new)
+
+/*
+ * Macros for breaking up a reserved element into two smaller chunks using an
+ * anonymous struct inside an anonymous union.
+ */
+#define ALI_HOTFIX_USE2(n, _new1, _new2)		\
+	ALI_HOTFIX_REPLACE(_ALI_HOTFIX_RESERVE(n), struct{ _new1; _new2; })
+#define ALI_HOTFIX_USE2_P(n, _new1, _new2)		\
+	ALI_HOTFIX_REPLACE(_ALI_HOTFIX_RESERVE_P(n), struct{ _new1; _new2; })
+
+#endif /* _LINUX_ALI_HOTFIX_H */

include/linux/backing-dev-defs.h

@@ -162,6 +162,9 @@ struct bdi_writeback {
 		struct rcu_head rcu;
 	};
 #endif
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
 };
 
 struct backing_dev_info {
@@ -205,6 +208,9 @@ struct backing_dev_info {
 	struct dentry *debug_dir;
 	struct dentry *debug_stats;
 #endif
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
 };
 
 enum {

include/linux/bio.h

@@ -775,6 +775,9 @@ struct bio_set {
 	struct bio_list		rescue_list;
 	struct work_struct	rescue_work;
 	struct workqueue_struct	*rescue_workqueue;
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
 };
 
 struct biovec_slab {

include/linux/blk-cgroup.h

@@ -58,6 +58,11 @@ struct blkcg {
 	struct list_head		cgwb_list;
 	refcount_t			cgwb_refcnt;
 #endif
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
+	ALI_HOTFIX_RESERVE(3)
+	ALI_HOTFIX_RESERVE(4)
 };
 
 /*
@@ -178,6 +183,9 @@ struct blkcg_policy {
 	blkcg_pol_free_pd_fn		*pd_free_fn;
 	blkcg_pol_reset_pd_stats_fn	*pd_reset_stats_fn;
 	blkcg_pol_stat_pd_fn		*pd_stat_fn;
+
+	ALI_HOTFIX_RESERVE_P(1)
+	ALI_HOTFIX_RESERVE_P(2)
 };
 
 extern struct blkcg blkcg_root;

include/linux/blk-mq.h

@@ -70,6 +70,11 @@ struct blk_mq_hw_ctx {
 	struct dentry		*sched_debugfs_dir;
 #endif
 
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
+	ALI_HOTFIX_RESERVE(3)
+	ALI_HOTFIX_RESERVE(4)
+
 	/* Must be the last member - see also blk_mq_hw_ctx_size(). */
 	struct srcu_struct	srcu[0];
 };
@@ -90,11 +95,18 @@ struct blk_mq_tag_set {
 
 	struct mutex		tag_list_lock;
 	struct list_head	tag_list;
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
+	ALI_HOTFIX_RESERVE(3)
+	ALI_HOTFIX_RESERVE(4)
 };
 
 struct blk_mq_queue_data {
 	struct request *rq;
 	bool last;
+
+	ALI_HOTFIX_RESERVE(1)
 };
 
 typedef blk_status_t (queue_rq_fn)(struct blk_mq_hw_ctx *,
@@ -181,6 +193,9 @@ struct blk_mq_ops {
 	 */
 	void (*show_rq)(struct seq_file *m, struct request *rq);
 #endif
+
+	ALI_HOTFIX_RESERVE_P(1)
+	ALI_HOTFIX_RESERVE_P(2)
 };
 
 enum {

include/linux/blk_types.h

@@ -11,6 +11,8 @@
 #include <linux/ktime.h>
 #include <linux/sched/clock.h>
 
+#include <linux/ali_hotfix.h>
+
 struct bio_set;
 struct bio;
 struct bio_integrity_payload;
@@ -212,6 +214,9 @@ struct bio {
 
 	struct bio_set		*bi_pool;
 
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
+
 	/*
 	 * We can inline a number of vecs at the end of the bio, to avoid
 	 * double allocations for a small number of bio_vecs. This member

include/linux/blkdev.h

@@ -396,6 +396,9 @@ struct queue_limits {
 	unsigned char		cluster;
 	unsigned char		raid_partial_stripes_expensive;
 	enum blk_zoned_model	zoned;
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
 };
 
 #ifdef CONFIG_BLK_DEV_ZONED
@@ -677,6 +680,11 @@ struct request_queue {
 
 #define BLK_MAX_WRITE_HINTS	5
 	u64			write_hints[BLK_MAX_WRITE_HINTS];
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
+	ALI_HOTFIX_RESERVE(3)
+	ALI_HOTFIX_RESERVE(4)
 };
 
 #define QUEUE_FLAG_QUEUED	0	/* uses generic tag queueing */

include/linux/cgroup-defs.h

@@ -161,6 +161,9 @@ struct cgroup_subsys_state {
 	struct work_struct destroy_work;
 	struct rcu_work destroy_rwork;
 
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
+
 	/*
 	 * PI: the parent css.	Placed here for cache proximity to following
 	 * fields of the containing structure.
@@ -262,6 +265,9 @@ struct css_set {
 
 	/* For RCU-protected deletion */
 	struct rcu_head rcu_head;
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
 };
 
 struct cgroup_base_stat {
@@ -489,6 +495,9 @@ struct cgroup_root {
 	/* IDs for cgroups in this hierarchy */
 	struct idr cgroup_idr;
 
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
+
 	/* The path to use for release notifications. */
 	char release_agent_path[PATH_MAX];
 
@@ -614,6 +623,9 @@ struct cgroup_subsys {
 	void (*release)(struct task_struct *task);
 	void (*bind)(struct cgroup_subsys_state *root_css);
 
+	ALI_HOTFIX_RESERVE_P(1)
+	ALI_HOTFIX_RESERVE_P(2)
+
 	bool early_init:1;
 
 	/*

include/linux/dcache.h

@@ -14,6 +14,8 @@
 #include <linux/stringhash.h>
 #include <linux/wait.h>
 
+#include <linux/ali_hotfix.h>
+
 struct path;
 struct vfsmount;
 
@@ -117,6 +119,9 @@ struct dentry {
 		struct hlist_bl_node d_in_lookup_hash;	/* only for in-lookup ones */
 	 	struct rcu_head d_rcu;
 	} d_u;
+
+	ALI_HOTFIX_RESERVE(1)
+	ALI_HOTFIX_RESERVE(2)
 } __randomize_layout;
 
 /*

include/linux/elevator.h

@@ -119,6 +119,9 @@ struct elevator_mq_ops {
 	struct request *(*next_request)(struct request_queue *, struct request *);
 	void (*init_icq)(struct io_cq *);
 	void (*exit_icq)(struct io_cq *);
+
+	ALI_HOTFIX_RESERVE_P(1)
+	ALI_HOTFIX_RESERVE_P(2)
 };
 
 #define ELV_NAME_MAX	(16)