Re: [PATCH v2 2/4] fprobe: make fprobe_kprobe_handler recursion free

[Google]

On Tue, 16 May 2023 17:47:52 +0800
Ze Gao <zegao2021@xxxxxxxxx> wrote:

> Precisely, these that are called within kprobe_busy_{begin, end},
> which the previous patch does not resolve.

Note that kprobe_busy_{begin,end} don't need to use notrace version
because kprobe itself prohibits probing on preempt_count_{add,sub}.

Thank you,

> I will refine the commit message to make it clear.
> 
> FYI, details can checked out here:
>     Link: https://lore.kernel.org/linux-trace-kernel/20230516132516.c902edcf21028874a74fb868@xxxxxxxxxx/
> 
> Regards,
> Ze
> 
> On Tue, May 16, 2023 at 5:18 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Tue, May 16, 2023 at 03:18:28PM +0800, Ze Gao wrote:
> > > Current implementation calls kprobe related functions before doing
> > > ftrace recursion check in fprobe_kprobe_handler, which opens door
> > > to kernel crash due to stack recursion if preempt_count_{add, sub}
> > > is traceable.
> >
> > Which preempt_count*() are you referring to? The ones you just made
> > _notrace in the previous patch?


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