# Re: \[PATCH v3 01/28\] module: Extend the preempt disabled section in dereference\_symbol\_descriptor().

- From: Helge Deller \<deller@gmx.de\>
- Date: 2025-01-08 09:55:45 
- List: linux-modules
- Page: https://ratatoskr.run/linux-modules/2025/01/2881283
- Thread: https://ratatoskr.run/linux-modules/2025/01/2881188/t.md

```text
On 1/8/25 10:04, Sebastian Andrzej Siewior wrote:
> dereference_symbol_descriptor() needs to obtain the module pointer
> belonging to pointer in order to resolve that pointer.
> The returned mod pointer is obtained under RCU-sched/ preempt_disable()
> guarantees and needs to be used within this section to ensure that the
> module is not removed in the meantime.
>
> Extend the preempt_disable() section to also cover
> dereference_module_function_descriptor().
>
> Fixes: 04b8eb7a4ccd9 ("symbol lookup: introduce dereference_symbol_descriptor()")
> Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
> Cc: Christophe Leroy <redacted>
> Cc: Helge Deller <deller@gmx.de>
> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Naveen N Rao <naveen@kernel.org>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Sergey Senozhatsky <redacted>
> Cc: <redacted>
> Cc: <redacted>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Nice catch.

Acked-by: Helge Deller <deller@gmx.de>

This patch really should be backported.
Can you add a Cc: stable tag?

Helge


> ---
>   include/linux/kallsyms.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
> index c3f075e8f60cb..1c6a6c1704d8d 100644
> --- a/include/linux/kallsyms.h
> +++ b/include/linux/kallsyms.h
> @@ -57,10 +57,10 @@ static inline void *dereference_symbol_descriptor(void *ptr)
>
>   	preempt_disable();
>   	mod = __module_address((unsigned long)ptr);
> -	preempt_enable();
>
>   	if (mod)
>   		ptr = dereference_module_function_descriptor(mod, ptr);
> +	preempt_enable();
>   #endif
>   	return ptr;
>   }

```