Re: [PATCH 1/2] x86: make profile_pc() use arch_stack_walk()

[Qi Zheng]

On 2023/4/8 12:56, Josh Poimboeuf wrote:
> On Thu, Mar 30, 2023 at 04:15:51PM +0800, Qi Zheng wrote:
> > The profile_pc() try to get pc by doing a trick to read
> > the contents of the stack. This may cause false positives
> > for KASAN, like the following:
> >
> >   BUG: KASAN: stack-out-of-bounds in profile_pc+0x5b/0x90
> >   Read of size 8 at addr ffff8881062a7a00 by task id/130040
>
> I don't think this was actually a false positive.  The !FRAME_POINTER
> code in profile_pc() has been badly broken for many years.
>
> BTW, there was a similar patch here:
>
>    https://lore.kernel.org/lkml/20230224021858.120078-1-chenzhongjin@xxxxxxxxxx/

Ah.

> I thought CONFIG_PROFILING was obsolete but Andi said previously he
> wants to keep it for at least boot-time profiling.
>
> Andi did suggest removing the lock profiling hacks, which means all the
> profile_pc() implementations can just be removed in favor of the generic
> instruction_pointer().

That's great, and I see Chen Zhongjin will send a new patch for this,
let him continue this work. :)

>

--
Thanks,
Qi