Re: WARNING: suspicious RCU usage in idtentry_exit

[Thomas Gleixner]

Dmitry,

Dmitry Vyukov <dvyukov@xxxxxxxxxx> writes:
> On Thu, May 28, 2020 at 10:48 PM Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
>> On Thu, May 28, 2020 at 10:19:02PM +0200, Thomas Gleixner wrote:
>> OK, from the .config, another suggestion is to build the kernel
>> with CONFIG_RCU_EQS_DEBUG=y.  This still requires that this issue be
>> reproduced, but it might catch the problem earlier.
>
> How much does it slow down execution? If we enable it on syzbot, it
> will affect all fuzzing done by syzbot always.
> It can tolerate significant slowdown and it's far from a production
> kernel (it enables KASAN, KCOV, LOCKDEP and more). But I am still
> asking because some debugging features are built without performance
> in mind at all (like let's just drop a global lock in every
> kmalloc/free, which may be too much even for a standard debug build).

It's not worse than lockdep.

Thanks,

        tglx