Re: [PATCH] mm/util.c: Make kvfree() safe for calling while holding spinlocks

[Manfred Spraul]

Hello Vasily,

On 12/23/21 08:21, Vasily Averin wrote:
> I would prefer to release memory ASAP if it's possible.
> What do you think about this change?
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -614,9 +614,12 @@ EXPORT_SYMBOL(kvmalloc_node);
>    */
>   void kvfree(const void *addr)
>   {
> -       if (is_vmalloc_addr(addr))
> -               vfree(addr);
> -       else
> +       if (is_vmalloc_addr(addr)) {
> +               if (in_atomic())
> +                       vfree_atomic();
> +               else
> +                       vfree(addr);
> +       } else
>                  kfree(addr);
>   }
>   EXPORT_SYMBOL(kvfree);
Unfortunately this cannot work:

> /*
> * Are we running in atomic context?  WARNING: this macro cannot
> * always detect atomic context; in particular, it cannot know about
> * held spinlocks in non-preemptible kernels.  Thus it should not be
> * used in the general case to determine whether sleeping is possible.
> * Do not use in_atomic() in driver code.
> */
> #define in_atomic()     (preempt_count() != 0)

--

    Manfred