From: Lorenzo Stoakes (Oracle) Date: Wed, 11 Mar 2026 17:24:37 +0000 (+0000) Subject: mm: abstract reading sysctl_max_map_count, and READ_ONCE() X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2d1e54aab6fd01f7502af20e125312e06a15bf9c;p=thirdparty%2Fkernel%2Flinux.git mm: abstract reading sysctl_max_map_count, and READ_ONCE() Concurrent reads and writes of sysctl_max_map_count are possible, so we should READ_ONCE() and WRITE_ONCE(). The sysctl procfs logic already enforces WRITE_ONCE(), so abstract the read side with get_sysctl_max_map_count(). While we're here, also move the field to mm/internal.h and add the getter there since only mm interacts with it, there's no need for anybody else to have access. Finally, update the VMA userland tests to reflect the change. Link: https://lkml.kernel.org/r/0715259eb37cbdfde4f9e5db92a20ec7110a1ce5.1773249037.git.ljs@kernel.org Signed-off-by: Lorenzo Stoakes (Oracle) Reviewed-by: Pedro Falcato Cc: Jann Horn Cc: Jianzhou Zhao Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Oscar Salvador Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- diff --git a/include/linux/mm.h b/include/linux/mm.h index efb8be5d259cc..25ba5816e02bc 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -207,8 +207,6 @@ static inline void __mm_zero_struct_page(struct page *page) #define MAPCOUNT_ELF_CORE_MARGIN (5) #define DEFAULT_MAX_MAP_COUNT (USHRT_MAX - MAPCOUNT_ELF_CORE_MARGIN) -extern int sysctl_max_map_count; - extern unsigned long sysctl_user_reserve_kbytes; extern unsigned long sysctl_admin_reserve_kbytes; diff --git a/mm/internal.h b/mm/internal.h index f50a0376b87e8..62d80fd37ae1f 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1863,4 +1863,10 @@ static inline int pmdp_test_and_clear_young_notify(struct vm_area_struct *vma, #endif /* CONFIG_MMU_NOTIFIER */ +extern int sysctl_max_map_count; +static inline int get_sysctl_max_map_count(void) +{ + return READ_ONCE(sysctl_max_map_count); +} + #endif /* __MM_INTERNAL_H */ diff --git a/mm/mmap.c b/mm/mmap.c index 843160946aa5f..79544d8934111 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -375,7 +375,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, return -EOVERFLOW; /* Too many mappings? */ - if (mm->map_count > sysctl_max_map_count) + if (mm->map_count > get_sysctl_max_map_count()) return -ENOMEM; /* diff --git a/mm/mremap.c b/mm/mremap.c index e8c3021dd841f..ba6c690f6c1ba 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -1045,7 +1045,7 @@ static unsigned long prep_move_vma(struct vma_remap_struct *vrm) * which may not merge, then (if MREMAP_DONTUNMAP is not set) unmap the * source, which may split, causing a net increase of 2 mappings. */ - if (current->mm->map_count + 2 > sysctl_max_map_count) + if (current->mm->map_count + 2 > get_sysctl_max_map_count()) return -ENOMEM; if (vma->vm_ops && vma->vm_ops->may_split) { @@ -1813,7 +1813,7 @@ static unsigned long check_mremap_params(struct vma_remap_struct *vrm) * net increased map count of 2. In move_vma() we check for headroom of * 2 additional mappings, so check early to avoid bailing out then. */ - if (current->mm->map_count + 4 > sysctl_max_map_count) + if (current->mm->map_count + 4 > get_sysctl_max_map_count()) return -ENOMEM; return 0; diff --git a/mm/nommu.c b/mm/nommu.c index c3a23b082adb9..ed3934bc2de48 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1317,7 +1317,7 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, return -ENOMEM; mm = vma->vm_mm; - if (mm->map_count >= sysctl_max_map_count) + if (mm->map_count >= get_sysctl_max_map_count()) return -ENOMEM; region = kmem_cache_alloc(vm_region_jar, GFP_KERNEL); diff --git a/mm/vma.c b/mm/vma.c index b7055c264b5d3..4d21e7d8e93c4 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -590,7 +590,7 @@ out_free_vma: static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, unsigned long addr, int new_below) { - if (vma->vm_mm->map_count >= sysctl_max_map_count) + if (vma->vm_mm->map_count >= get_sysctl_max_map_count()) return -ENOMEM; return __split_vma(vmi, vma, addr, new_below); @@ -1394,7 +1394,7 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, * its limit temporarily, to help free resources as expected. */ if (vms->end < vms->vma->vm_end && - vms->vma->vm_mm->map_count >= sysctl_max_map_count) { + vms->vma->vm_mm->map_count >= get_sysctl_max_map_count()) { error = -ENOMEM; goto map_count_exceeded; } @@ -2868,7 +2868,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma, if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) return -ENOMEM; - if (mm->map_count > sysctl_max_map_count) + if (mm->map_count > get_sysctl_max_map_count()) return -ENOMEM; if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT)) diff --git a/tools/testing/vma/include/custom.h b/tools/testing/vma/include/custom.h index 7150e09122b27..6c62a38a2f6f6 100644 --- a/tools/testing/vma/include/custom.h +++ b/tools/testing/vma/include/custom.h @@ -21,9 +21,6 @@ extern unsigned long dac_mmap_min_addr; #define VM_BUG_ON(_expr) (BUG_ON(_expr)) #define VM_BUG_ON_VMA(_expr, _vma) (BUG_ON(_expr)) -/* We hardcode this for now. */ -#define sysctl_max_map_count 0x1000000UL - #define TASK_SIZE ((1ul << 47)-PAGE_SIZE) /* diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index 5eb313beb43de..8865ffe046d81 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -419,6 +419,9 @@ struct vma_iterator { #define EMPTY_VMA_FLAGS ((vma_flags_t){ }) +#define MAPCOUNT_ELF_CORE_MARGIN (5) +#define DEFAULT_MAX_MAP_COUNT (USHRT_MAX - MAPCOUNT_ELF_CORE_MARGIN) + /* What action should be taken after an .mmap_prepare call is complete? */ enum mmap_action_type { MMAP_NOTHING, /* Mapping is complete, no further action. */ @@ -1342,3 +1345,9 @@ static inline void vma_set_file(struct vm_area_struct *vma, struct file *file) swap(vma->vm_file, file); fput(file); } + +extern int sysctl_max_map_count; +static inline int get_sysctl_max_map_count(void) +{ + return READ_ONCE(sysctl_max_map_count); +} diff --git a/tools/testing/vma/main.c b/tools/testing/vma/main.c index 49b09e97a51ff..18338f5d29e00 100644 --- a/tools/testing/vma/main.c +++ b/tools/testing/vma/main.c @@ -14,6 +14,8 @@ #include "tests/mmap.c" #include "tests/vma.c" +int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT; + /* Helper functions which utilise static kernel functions. */ struct vm_area_struct *merge_existing(struct vma_merge_struct *vmg)