On Thu, May 14, 2020 at 10:03:21AM -0400, Qian Cai wrote:
>
>
> > On May 14, 2020, at 9:54 AM, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
> >
> > On Thu, May 14, 2020 at 09:44:28AM -0400, Qian Cai wrote:
> >>
> >>
> >>> On May 14, 2020, at 9:33 AM, Paul E. McKenney <paulmck@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxx> 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?
> >
> > Sound good to me, assuming that this works for the syzkaller guys.
> > Or could there be a "select PROVE_RCU_LIST" for the people who would
> > like to test it.
> >
> > Alternatively, if we revert d13fee049fa8 from -next, I could provide
> > you a script that updates your .config to set both RCU_EXPERT and
> > PROVE_RCU_LIST.
> >
> > There are a lot of ways to appraoch this.
> >
> > So what would work best for everyone?
>
>
> If PROVE_RCU_LIST=n if DEBUG_AID_FOR_SYZBOT works for syzbot guys, that would be great, so other testing agents could still report/fix those RCU-list bugs and then pave a way for syzbot to return back once all those false positives had been sorted out.
On that, I must defer to the syzbot guys.
> Otherwise, “select PROVE_RCU_LIST” *might* be better than buried into RCU_EXPERT where we will probably never saw those false positives been addressed since my configs does not cover a wide range of subsystems and probably not many other bots would enable RCU_EXPERT.
Yet another option would be to edit your local kernel/rcu/Kconfig.debug
and change the code to the following:
config PROVE_RCU_LIST
def_bool y
help
Enable RCU lockdep checking for list usages. It is default
enabled with CONFIG_PROVE_RCU.
Removing the RCU_EXPERT dependency would not go over at all well with
some people whose opinions are difficult to ignore. ;-)
Thanx, Paul
