linux-kernel - Re: [PATCH v3 2/2] sched/numa: Add tracepoint that tracks the skipping of numa balancing due to cpuset memory pinning

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Message-ID: <8C830352-11B1-4D7C-84C4-F5D5F7008F63@oracle.com>
Date: Wed, 23 Apr 2025 18:22:54 +0000
From: Libo Chen <libo.chen@...cle.com>
To: Steven Rostedt <rostedt@...dmis.org>
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Subject: Re: [PATCH v3 2/2] sched/numa: Add tracepoint that tracks the
 skipping of numa balancing due to cpuset memory pinning



> On Apr 23, 2025, at 9:56 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Wed, 23 Apr 2025 16:50:15 +0000
> Libo Chen <libo.chen@...cle.com> wrote:
> 
>> Correct me if I'm wrong but can you disallow any passed-in pointers to be
>> dereferenced when TP_printk() is executed? This is something you can check
>> at the build time, right?
> 
> You can dereference if the pointer is to the content on the ring buffer.
> For instance, you can have:
> 
>  "%p*h", &__entry->val
> 
> It dereferences to the content stored on the ring buffer.
> 
> What we can't have is:
> 
>  "%p*h", __entry->val

Right, I was thinking something stricter such as disallowing point-type
field in TP_STRUCT__entry {} to avoid direct assignment to point-type
field so there will be no chance to have unsafe dereference but then I
realize C doesn’t have built-in mechanism to detect various types of
pointers at the compile time, maybe rust can do that. Anyway I give up.

Thanks,
Libo

> 
> -- Steve