Re: Default enable RCU list lockdep debugging with PROVE_RCU

Qian Cai
2020-05-14T13:44:31Z

> On May 14, 2020, at 9:33 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
>>
>>
>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>>>
>>> Hi Paul,
>>>
>>> This patch in the rcu tree
>>>
>>> d13fee049fa8 ("Default enable RCU list lockdep debugging with PROVE_RCU")
>>>
>>> is causing whack-a-mole in the syzbot testing of linux-next. Because
>>> they always do a debug build of linux-next, no testing is getting done. :-(
>>>
>>> Can we find another way to find all the bugs that are being discovered
>>> (very slowly)?
>>
>> Alternatively, could syzbot to use PROVE_RCU=n temporarily because it can’t keep up with it? I personally found PROVE_RCU_LIST=y is still useful for my linux-next testing, and don’t want to lose that coverage overnight.
>
> The problem is that PROVE_RCU is exactly PROVE_LOCKING, and asking people
> to test without PROVE_LOCKING is a no-go in my opinion. But of course
> on the other hand if there is no testing of RCU list lockdep debugging,
> those issues will never be found, let alone fixed.
>
> One approach would be to do as Stephen asks (either remove d13fee049fa8
> or pull it out of -next) and have testers force-enable the RCU list
> lockdep debugging.
>
> Would that work for you?

Alternatively, how about having

PROVE_RCU_LIST=n if DEBUG_AID_FOR_SYZBOT

since it is only syzbot can’t keep up with it?