Re: [RFC 03/14] fork: Clean-up naming of vm_strack/vm_struct variables in vmap stacks code

[Christophe JAILLET]

Le 11/03/2024 à 17:46, Pasha Tatashin a écrit :
> There are two data types: "struct vm_struct" and "struct vm_stack" that
> have the same local variable names: vm_stack, or vm, or s, which makes
> code confusing to read.
>
> Change the code so the naming is consisent:

Nit: consistent

> struct vm_struct is always called vm_area
> struct vm_stack is always called vm_stack
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> ---
>   kernel/fork.c | 38 ++++++++++++++++++--------------------
>   1 file changed, 18 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 32600bf2422a..60e812825a7a 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -192,12 +192,12 @@ struct vm_stack {
>   	struct vm_struct *stack_vm_area;
>   };
>   
> -static bool try_release_thread_stack_to_cache(struct vm_struct *vm)
> +static bool try_release_thread_stack_to_cache(struct vm_struct *vm_area)
>   {
>   	unsigned int i;
>   
>   	for (i = 0; i < NR_CACHED_STACKS; i++) {
> -		if (this_cpu_cmpxchg(cached_stacks[i], NULL, vm) != NULL)
> +		if (this_cpu_cmpxchg(cached_stacks[i], NULL, vm_area) != NULL)
>   			continue;
>   		return true;
>   	}
> @@ -207,11 +207,12 @@ static bool try_release_thread_stack_to_cache(struct vm_struct *vm)
>   static void thread_stack_free_rcu(struct rcu_head *rh)
>   {
>   	struct vm_stack *vm_stack = container_of(rh, struct vm_stack, rcu);
> +	struct vm_struct *vm_area = vm_stack->stack_vm_area;
>   
>   	if (try_release_thread_stack_to_cache(vm_stack->stack_vm_area))
>   		return;
>   
> -	vfree(vm_stack);
> +	vfree(vm_area->addr);

This does not look like only a renaming of a variable. Is it?

If no, should there be a Fixes tag and should it be detailed in the 
commit description?

CJ

>   }
>   
>   static void thread_stack_delayed_free(struct task_struct *tsk)
> @@ -228,12 +229,12 @@ static int free_vm_stack_cache(unsigned int cpu)
>   	int i;
>   
>   	for (i = 0; i < NR_CACHED_STACKS; i++) {
> -		struct vm_struct *vm_stack = cached_vm_stacks[i];
> +		struct vm_struct *vm_area = cached_vm_stacks[i];
>   
> -		if (!vm_stack)
> +		if (!vm_area)
>   			continue;
>   
> -		vfree(vm_stack->addr);
> +		vfree(vm_area->addr);
>   		cached_vm_stacks[i] = NULL;
>   	}
>   
> @@ -263,32 +264,29 @@ static int memcg_charge_kernel_stack(struct vm_struct *vm)
>   
>   static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>   {
> -	struct vm_struct *vm;
> +	struct vm_struct *vm_area;
>   	void *stack;
>   	int i;
>   
>   	for (i = 0; i < NR_CACHED_STACKS; i++) {
> -		struct vm_struct *s;
> -
> -		s = this_cpu_xchg(cached_stacks[i], NULL);
> -
> -		if (!s)
> +		vm_area = this_cpu_xchg(cached_stacks[i], NULL);
> +		if (!vm_area)
>   			continue;
>   
>   		/* Reset stack metadata. */
> -		kasan_unpoison_range(s->addr, THREAD_SIZE);
> +		kasan_unpoison_range(vm_area->addr, THREAD_SIZE);
>   
> -		stack = kasan_reset_tag(s->addr);
> +		stack = kasan_reset_tag(vm_area->addr);
>   
>   		/* Clear stale pointers from reused stack. */
>   		memset(stack, 0, THREAD_SIZE);
>   
> -		if (memcg_charge_kernel_stack(s)) {
> -			vfree(s->addr);
> +		if (memcg_charge_kernel_stack(vm_area)) {
> +			vfree(vm_area->addr);
>   			return -ENOMEM;
>   		}
>   
> -		tsk->stack_vm_area = s;
> +		tsk->stack_vm_area = vm_area;
>   		tsk->stack = stack;
>   		return 0;
>   	}
> @@ -306,8 +304,8 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>   	if (!stack)
>   		return -ENOMEM;
>   
> -	vm = find_vm_area(stack);
> -	if (memcg_charge_kernel_stack(vm)) {
> +	vm_area = find_vm_area(stack);
> +	if (memcg_charge_kernel_stack(vm_area)) {
>   		vfree(stack);
>   		return -ENOMEM;
>   	}
> @@ -316,7 +314,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>   	 * free_thread_stack() can be called in interrupt context,
>   	 * so cache the vm_struct.
>   	 */
> -	tsk->stack_vm_area = vm;
> +	tsk->stack_vm_area = vm_area;
>   	stack = kasan_reset_tag(stack);
>   	tsk->stack = stack;
>   	return 0;