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

[Pasha Tatashin]

On Sun, Mar 17, 2024 at 10:42 AM Christophe JAILLET
<christophe.jaillet@xxxxxxxxxx> wrote:
>
> 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?

This change is only for readability purposes. vm_stack is stored in
vm_area, so vfree(vm_stack) equals to vfree(vm_area->addr), but is
hard to read. I will add it to changelog.

>
> 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;
>