Re: [PATCH v3 26/28] kprobes: Use RCU in all users of __module_text_address().

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On Wed,  8 Jan 2025 10:04:55 +0100
Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:

> __module_text_address() can be invoked within a RCU section, there is no
> requirement to have preemption disabled.
> 
> Replace the preempt_disable() section around __module_text_address()
> with RCU.

Hi,

Since the below cleanup has been merged, this patch needs to be updated.

https://lore.kernel.org/all/20241121-kprobes-preempt-v1-1-fd581ee7fcbb@xxxxxxxxxxxxx/

(may need to change the guard(preempt)() -> guard(rcu)() in the new version.)

Thank you,

> 
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Naveen N Rao <naveen@xxxxxxxxxx>
> Cc: linux-trace-kernel@xxxxxxxxxxxxxxx
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
>  kernel/kprobes.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index b027a4030976a..22e47a27df4aa 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1566,7 +1566,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  	if (ret)
>  		return ret;
>  	jump_label_lock();
> -	preempt_disable();
> +	rcu_read_lock();
>  
>  	/* Ensure the address is in a text area, and find a module if exists. */
>  	*probed_mod = NULL;
> @@ -1612,7 +1612,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  	}
>  
>  out:
> -	preempt_enable();
> +	rcu_read_unlock();
>  	jump_label_unlock();
>  
>  	return ret;
> -- 
> 2.47.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>