mm: constify oom_control, scan_control, and alloc_context nodemask

The nodemasks in these structures may come from a variety of sources,
including tasks and cpusets - and should never be modified by any code
when being passed around inside another context.

Link: https://lore.kernel.org/20260609002919.3967782-1-gourry@gourry.net
Signed-off-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Tested-by: SeongJae Park <sj@kernel.org>
Acked-by: SeongJae Park <sj@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/cpuset.h

@@ -83,7 +83,7 @@ extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
-int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask);
+int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask);
 
 extern bool cpuset_current_node_allowed(int node, gfp_t gfp_mask);
 
@@ -224,7 +224,7 @@ static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
 #define cpuset_current_mems_allowed (node_states[N_MEMORY])
 static inline void cpuset_init_current_mems_allowed(void) {}
 
-static inline int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
+static inline int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask)
 {
 	return 1;
 }

include/linux/mm.h

@@ -4042,7 +4042,7 @@ extern int __meminit early_pfn_to_nid(unsigned long pfn);
 extern void mem_init(void);
 extern void __init mmap_init(void);
 
-extern void __show_mem(unsigned int flags, nodemask_t *nodemask, int max_zone_idx);
+extern void __show_mem(unsigned int flags, const nodemask_t *nodemask, int max_zone_idx);
 static inline void show_mem(void)
 {
 	__show_mem(0, NULL, MAX_NR_ZONES - 1);
@@ -4052,7 +4052,7 @@ extern void si_meminfo(struct sysinfo * val);
 extern void si_meminfo_node(struct sysinfo *val, int nid);
 
 extern __printf(3, 4)
-void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...);
+void warn_alloc(gfp_t gfp_mask, const nodemask_t *nodemask, const char *fmt, ...);
 
 extern void setup_per_cpu_pageset(void);
 

include/linux/mmzone.h

@@ -1815,7 +1815,7 @@ static inline int zonelist_node_idx(const struct zoneref *zoneref)
 
 struct zoneref *__next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes);
+					const nodemask_t *nodes);
 
 /**
  * next_zones_zonelist - Returns the next zone at or below highest_zoneidx within the allowed nodemask using a cursor within a zonelist as a starting point
@@ -1834,7 +1834,7 @@ struct zoneref *__next_zones_zonelist(struct zoneref *z,
  */
 static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes)
+					const nodemask_t *nodes)
 {
 	if (likely(!nodes && zonelist_zone_idx(z) <= highest_zoneidx))
 		return z;
@@ -1860,7 +1860,7 @@ static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
  */
 static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes)
+					const nodemask_t *nodes)
 {
 	return next_zones_zonelist(zonelist->_zonerefs,
 							highest_zoneidx, nodes);

include/linux/oom.h

@@ -30,7 +30,7 @@ struct oom_control {
 	struct zonelist *zonelist;
 
 	/* Used to determine mempolicy */
-	nodemask_t *nodemask;
+	const nodemask_t *nodemask;
 
 	/* Memory cgroup in which oom is invoked, or NULL for global oom */
 	struct mem_cgroup *memcg;

include/linux/swap.h

@@ -345,7 +345,7 @@ extern void swap_setup(void);
 /* linux/mm/vmscan.c */
 extern unsigned long zone_reclaimable_pages(struct zone *zone);
 extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
-					gfp_t gfp_mask, nodemask_t *mask);
+					gfp_t gfp_mask, const nodemask_t *mask);
 unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx);
 
 #define MEMCG_RECLAIM_MAY_SWAP (1 << 1)

kernel/cgroup/cpuset.c

@@ -4162,7 +4162,7 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
  *
  * Are any of the nodes in the nodemask allowed in current->mems_allowed?
  */
-int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
+int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask)
 {
 	return nodes_intersects(*nodemask, current->mems_allowed);
 }

mm/internal.h

@@ -675,7 +675,7 @@ void page_alloc_sysctl_init(void);
  */
 struct alloc_context {
 	struct zonelist *zonelist;
-	nodemask_t *nodemask;
+	const nodemask_t *nodemask;
 	struct zoneref *preferred_zoneref;
 	int migratetype;
 

mm/mmzone.c

@@ -43,7 +43,8 @@ struct zone *next_zone(struct zone *zone)
 	return zone;
 }
 
-static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
+static inline int zref_in_nodemask(struct zoneref *zref,
+				   const nodemask_t *nodes)
 {
 #ifdef CONFIG_NUMA
 	return node_isset(zonelist_node_idx(zref), *nodes);
@@ -55,7 +56,7 @@ static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
 /* Returns the next zone at or below highest_zoneidx in a zonelist */
 struct zoneref *__next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes)
+					const nodemask_t *nodes)
 {
 	/*
 	 * Find the next suitable zone to use for the allocation.

mm/page_alloc.c

@@ -3978,7 +3978,7 @@ try_this_zone:
 	return NULL;
 }
 
-static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
+static void warn_alloc_show_mem(gfp_t gfp_mask, const nodemask_t *nodemask)
 {
 	unsigned int filter = SHOW_MEM_FILTER_NODES;
 
@@ -3998,7 +3998,7 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
 	mem_cgroup_show_protected_memory(NULL);
 }
 
-void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
+void warn_alloc(gfp_t gfp_mask, const nodemask_t *nodemask, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -4680,7 +4680,7 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
 	return false;
 }
 
-static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
+static void check_alloc_stall_warn(gfp_t gfp_mask, const nodemask_t *nodemask,
 				unsigned int order, unsigned long alloc_start_time)
 {
 	static DEFINE_SPINLOCK(alloc_stall_lock);

mm/show_mem.c

@@ -116,7 +116,8 @@ void si_meminfo_node(struct sysinfo *val, int nid)
  * Determine whether the node should be displayed or not, depending on whether
  * SHOW_MEM_FILTER_NODES was passed to show_free_areas().
  */
-static bool show_mem_node_skip(unsigned int flags, int nid, nodemask_t *nodemask)
+static bool show_mem_node_skip(unsigned int flags, int nid,
+			       const nodemask_t *nodemask)
 {
 	if (!(flags & SHOW_MEM_FILTER_NODES))
 		return false;
@@ -177,7 +178,8 @@ static bool node_has_managed_zones(pg_data_t *pgdat, int max_zone_idx)
  * SHOW_MEM_FILTER_NODES: suppress nodes that are not allowed by current's
  *   cpuset.
  */
-static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
+static void show_free_areas(unsigned int filter, const nodemask_t *nodemask,
+			    int max_zone_idx)
 {
 	unsigned long free_pcp = 0;
 	int cpu, nid;
@@ -402,7 +404,8 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 	show_swap_cache_info();
 }
 
-void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
+void __show_mem(unsigned int filter, const nodemask_t *nodemask,
+		int max_zone_idx)
 {
 	unsigned long total = 0, reserved = 0, highmem = 0;
 	struct zone *zone;

mm/vmscan.c

@@ -79,7 +79,7 @@ struct scan_control {
 	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
 	 * are scanned.
 	 */
-	nodemask_t	*nodemask;
+	const nodemask_t *nodemask;
 
 	/*
 	 * The memory cgroup that hit its limit and as a result is the
@@ -6591,7 +6591,7 @@ static bool allow_direct_reclaim(pg_data_t *pgdat)
  * happens, the page allocator should not consider triggering the OOM killer.
  */
 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
-					nodemask_t *nodemask)
+				    const nodemask_t *nodemask)
 {
 	struct zoneref *z;
 	struct zone *zone;
@@ -6671,7 +6671,7 @@ out:
 }
 
 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
-				gfp_t gfp_mask, nodemask_t *nodemask)
+				gfp_t gfp_mask, const nodemask_t *nodemask)
 {
 	unsigned long nr_reclaimed;
 	struct scan_control sc = {