Re: [PATCH rcu 07/12] rcu: tiny: Record kvfree_call_rcu() call stack for KASAN

[Neeraj Upadhyay]

On 6/21/2022 3:50 AM, Paul E. McKenney wrote:
> From: Johannes Berg <johannes.berg@xxxxxxxxx>
>
> When running KASAN with Tiny RCU (e.g. under ARCH=um, where
> a working KASAN patch is now available), we don't get any
> information on the original kfree_rcu() (or similar) caller
> when a problem is reported, as Tiny RCU doesn't record this.
>
> Add the recording, which required pulling kvfree_call_rcu()
> out of line for the KASAN case since the recording function
> (kasan_record_aux_stack_noalloc) is neither exported, nor
> can we include kasan.h into rcutiny.h.
>
> without KASAN, the patch has no size impact (ARCH=um kernel):
>      text       data         bss         dec        hex    filename
>   6151515    4423154    33148520    43723189    29b29b5    linux
>   6151515    4423154    33148520    43723189    29b29b5    linux + patch
>
> with KASAN, the impact on my build was minimal:
>      text       data         bss         dec        hex    filename
> 13915539    7388050    33282304    54585893    340ea25    linux
> 13911266    7392114    33282304    54585684    340e954    linux + patch
>     -4273      +4064         +-0        -209
>
> Acked-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
>   include/linux/rcutiny.h | 11 ++++++++++-
>   kernel/rcu/tiny.c       | 14 ++++++++++++++
>   2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 5fed476f977f6..d84e13f2c3848 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -38,7 +38,7 @@ static inline void synchronize_rcu_expedited(void)
>    */
>   extern void kvfree(const void *addr);
>   
> -static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> +static inline void __kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
>   {
>   	if (head) {
>   		call_rcu(head, func);
> @@ -51,6 +51,15 @@ static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
>   	kvfree((void *) func);
>   }
>   
> +#ifdef CONFIG_KASAN_GENERIC
> +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
> +#else
> +static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> +{
> +	__kvfree_call_rcu(head, func);
> +}
> +#endif
> +
>   void rcu_qs(void);
>   
>   static inline void rcu_softirq_qs(void)
> diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
> index 340b3f8b090d4..58ff3721d975c 100644
> --- a/kernel/rcu/tiny.c
> +++ b/kernel/rcu/tiny.c
> @@ -217,6 +217,20 @@ bool poll_state_synchronize_rcu(unsigned long oldstate)
>   }
>   EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
>   
> +#ifdef CONFIG_KASAN_GENERIC
> +void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> +{
> +	if (head) {
> +		void *ptr = (void *) head - (unsigned long) func;
> +
> +		kasan_record_aux_stack_noalloc(ptr);
> +	}

For the !head case; similar to Tree RCU's kvfree_call_rcu() 
implementation, we do not need to record 'ptr' (which will be 'func')?


Thanks
Neeraj

> +
> +	__kvfree_call_rcu(head, func);
> +}
> +EXPORT_SYMBOL_GPL(kvfree_call_rcu);
> +#endif
> +
>   void __init rcu_init(void)
>   {
>   	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);