[PATCH v7 16/17] mm: make vma cache SLAB_TYPESAFE_BY_RCU

Suren Baghdasaryan
2024-12-26T17:07:56Z

To enable SLAB_TYPESAFE_BY_RCU for vma cache we need to ensure that
object reuse before RCU grace period is over will be detected by
lock_vma_under_rcu(). Current checks are sufficient as long as vma
is detached before it is freed. Implement this guarantee by calling
vma_ensure_detached() before vma is freed and make vm_area_cachep
SLAB_TYPESAFE_BY_RCU. This will facilitate vm_area_struct reuse and
will minimize the number of call_rcu() calls.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/mm.h | 2 --
include/linux/mm_types.h | 10 +++++++---
include/linux/slab.h | 6 ------
kernel/fork.c | 31 +++++++++----------------------
mm/mmap.c | 3 ++-
mm/vma.c | 10 +++-------
mm/vma.h | 2 +-
tools/testing/vma/vma_internal.h | 7 +------
8 files changed, 23 insertions(+), 48 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 56a7d70ca5bd..017d70e1d432 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -258,8 +258,6 @@ void setup_initial_init_mm(void *start_code, void *end_code,
struct vm_area_struct *vm_area_alloc(struct mm_struct *);
struct vm_area_struct *vm_area_dup(struct vm_area_struct *);
void vm_area_free(struct vm_area_struct *);
-/* Use only if VMA has no other users */
-void __vm_area_free(struct vm_area_struct *vma);

#ifndef CONFIG_MMU
extern struct rb_root nommu_region_tree;
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index b5312421dec6..3ca4695f6d0f 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -574,6 +574,12 @@ static inline void *folio_get_private(struct folio *folio)

typedef unsigned long vm_flags_t;

+/*
+ * freeptr_t represents a SLUB freelist pointer, which might be encoded
+ * and not dereferenceable if CONFIG_SLAB_FREELIST_HARDENED is enabled.
+ */
+typedef struct { unsigned long v; } freeptr_t;
+
/*
* A region containing a mapping of a non-memory backed file under NOMMU
* conditions. These are held in a global tree and are pinned by the VMAs that
@@ -687,9 +693,7 @@ struct vm_area_struct {
unsigned long vm_start;
unsigned long vm_end;
};
-#ifdef CONFIG_PER_VMA_LOCK
- struct rcu_head vm_rcu; /* Used for deferred freeing. */
-#endif
+ freeptr_t vm_freeptr; /* Pointer used by SLAB_TYPESAFE_BY_RCU */
};

/*
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 10a971c2bde3..681b685b6c4e 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -234,12 +234,6 @@ enum _slab_flag_bits {
#define SLAB_NO_OBJ_EXT __SLAB_FLAG_UNUSED
#endif

-/*
- * freeptr_t represents a SLUB freelist pointer, which might be encoded
- * and not dereferenceable if CONFIG_SLAB_FREELIST_HARDENED is enabled.
- */
-typedef struct { unsigned long v; } freeptr_t;
-
/*
* ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
*
diff --git a/kernel/fork.c b/kernel/fork.c
index 7a0800d48112..da3b1ebfd282 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -471,7 +471,7 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
return new;
}

-void __vm_area_free(struct vm_area_struct *vma)
+void vm_area_free(struct vm_area_struct *vma)
{
/* The vma should be detached while being destroyed. */
vma_assert_detached(vma);
@@ -480,25 +480,6 @@ void __vm_area_free(struct vm_area_struct *vma)
kmem_cache_free(vm_area_cachep, vma);
}

-#ifdef CONFIG_PER_VMA_LOCK
-static void vm_area_free_rcu_cb(struct rcu_head *head)
-{
- struct vm_area_struct *vma = container_of(head, struct vm_area_struct,
- vm_rcu);
-
- __vm_area_free(vma);
-}
-#endif
-
-void vm_area_free(struct vm_area_struct *vma)
-{
-#ifdef CONFIG_PER_VMA_LOCK
- call_rcu(&vma->vm_rcu, vm_area_free_rcu_cb);
-#else
- __vm_area_free(vma);
-#endif
-}
-
static void account_kernel_stack(struct task_struct *tsk, int account)
{
if (IS_ENABLED(CONFIG_VMAP_STACK)) {
@@ -3144,6 +3125,11 @@ void __init mm_cache_init(void)

void __init proc_caches_init(void)
{
+ struct kmem_cache_args args = {
+ .use_freeptr_offset = true,
+ .freeptr_offset = offsetof(struct vm_area_struct, vm_freeptr),
+ };
+
sighand_cachep = kmem_cache_create("sighand_cache",
sizeof(struct sighand_struct), 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
@@ -3160,8 +3146,9 @@ void __init proc_caches_init(void)
sizeof(struct fs_struct), 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
NULL);
- vm_area_cachep = KMEM_CACHE(vm_area_struct,
- SLAB_HWCACHE_ALIGN|SLAB_NO_MERGE|SLAB_PANIC|
+ vm_area_cachep = kmem_cache_create("vm_area_struct",
+ sizeof(struct vm_area_struct), &args,
+ SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
SLAB_ACCOUNT);
mmap_init();
nsproxy_cache_init();
diff --git a/mm/mmap.c b/mm/mmap.c
index 3cc8de07411d..7fdc4207fe98 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1364,7 +1364,8 @@ void exit_mmap(struct mm_struct *mm)
do {
if (vma->vm_flags & VM_ACCOUNT)
nr_accounted += vma_pages(vma);
- remove_vma(vma, /* unreachable = */ true);
+ vma_mark_detached(vma);
+ remove_vma(vma);
count++;
cond_resched();
vma = vma_next(&vmi);
diff --git a/mm/vma.c b/mm/vma.c
index 4a3deb6f9662..e37eb384d118 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -406,18 +406,14 @@ static bool can_vma_merge_right(struct vma_merge_struct *vmg,
/*
* Close a vm structure and free it.
*/
-void remove_vma(struct vm_area_struct *vma, bool unreachable)
+void remove_vma(struct vm_area_struct *vma)
{
might_sleep();
vma_close(vma);
if (vma->vm_file)
fput(vma->vm_file);
mpol_put(vma_policy(vma));
- if (unreachable) {
- vma_mark_detached(vma);
- __vm_area_free(vma);
- } else
- vm_area_free(vma);
+ vm_area_free(vma);
}

/*
@@ -1199,7 +1195,7 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
/* Remove and clean up vmas */
mas_set(mas_detach, 0);
mas_for_each(mas_detach, vma, ULONG_MAX)
- remove_vma(vma, /* unreachable = */ false);
+ remove_vma(vma);

vm_unacct_memory(vms->nr_accounted);
validate_mm(mm);
diff --git a/mm/vma.h b/mm/vma.h
index 18c9e49b1eae..d6803626151d 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -173,7 +173,7 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
unsigned long start, size_t len, struct list_head *uf,
bool unlock);

-void remove_vma(struct vm_area_struct *vma, bool unreachable);
+void remove_vma(struct vm_area_struct *vma);

void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
struct vm_area_struct *prev, struct vm_area_struct *next);
diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index 1e8cd2f013fa..c7c580ec9a2d 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h
@@ -693,14 +693,9 @@ static inline void mpol_put(struct mempolicy *)
{
}

-static inline void __vm_area_free(struct vm_area_struct *vma)
-{
- free(vma);
-}
-
static inline void vm_area_free(struct vm_area_struct *vma)
{
- __vm_area_free(vma);
+ free(vma);
}

static inline void lru_add_drain(void)
--
2.47.1.613.gc27f4b7a9f-goog