Re: Default enable RCU list lockdep debugging with PROVE_RCU
On Mon, May 18, 2020 at 01:54:13PM +0800, Rong Chen wrote: > > > On 5/18/20 5:47 AM, Paul E. McKenney wrote: > > On Fri, May 15, 2020 at 02:36:26PM -0400, Qian Cai wrote: > > > > > > > On May 14, 2020, at 2:13 PM, Paul E. McKenney > > > > wrote: > > > > > > > > Fair enough! And yes, the Linux kernel is quite large, so I certainly > > > > am > > > > not asking you to test the whole thing yourself. > > > Ok, I saw 0day bot also started to report those which is good. For > > > example, > > > > > > lkml.org/lkml/2020/5/12/1358 > > > > > > which so far is nit blocking 0day on linux-next since it does not use > > > panic_on_warn yet (while syzbot does). > > > > > > Thus, I am more convinced that we should not revert the commit just for > > > syzbot until someone could also convince 0day to select RCU_EXPERT and > > > then DEBUG_RCU_LIST? > > Let's ask the 0day people, now CCed, if they would be willing to > > build with CONFIG_RCU_EXPERT=y and CONFIG_DEBUG_RCU_LIST=y on some > > fraction of their testing. ;-) > > > > Thanx, Paul > > Hi, > > Thanks for your advice, we'll support it in the near future. Thank you very much! Thanx, Paul
Re: Default enable RCU list lockdep debugging with PROVE_RCU
On 5/18/20 5:47 AM, Paul E. McKenney wrote: On Fri, May 15, 2020 at 02:36:26PM -0400, Qian Cai wrote: On May 14, 2020, at 2:13 PM, Paul E. McKenney wrote: Fair enough! And yes, the Linux kernel is quite large, so I certainly am not asking you to test the whole thing yourself. Ok, I saw 0day bot also started to report those which is good. For example, lkml.org/lkml/2020/5/12/1358 which so far is nit blocking 0day on linux-next since it does not use panic_on_warn yet (while syzbot does). Thus, I am more convinced that we should not revert the commit just for syzbot until someone could also convince 0day to select RCU_EXPERT and then DEBUG_RCU_LIST? Let's ask the 0day people, now CCed, if they would be willing to build with CONFIG_RCU_EXPERT=y and CONFIG_DEBUG_RCU_LIST=y on some fraction of their testing. ;-) Thanx, Paul Hi, Thanks for your advice, we'll support it in the near future. Best Regards, Rong Chen
Re: Default enable RCU list lockdep debugging with PROVE_RCU
On Fri, May 15, 2020 at 02:36:26PM -0400, Qian Cai wrote: > > > > On May 14, 2020, at 2:13 PM, Paul E. McKenney wrote: > > > > Fair enough! And yes, the Linux kernel is quite large, so I certainly am > > not asking you to test the whole thing yourself. > > Ok, I saw 0day bot also started to report those which is good. For example, > > lkml.org/lkml/2020/5/12/1358 > > which so far is nit blocking 0day on linux-next since it does not use > panic_on_warn yet (while syzbot does). > > Thus, I am more convinced that we should not revert the commit just for > syzbot until someone could also convince 0day to select RCU_EXPERT and then > DEBUG_RCU_LIST? Let's ask the 0day people, now CCed, if they would be willing to build with CONFIG_RCU_EXPERT=y and CONFIG_DEBUG_RCU_LIST=y on some fraction of their testing. ;-) Thanx, Paul
Re: Default enable RCU list lockdep debugging with PROVE_RCU
> On May 14, 2020, at 2:13 PM, Paul E. McKenney wrote: > > Fair enough! And yes, the Linux kernel is quite large, so I certainly am > not asking you to test the whole thing yourself. Ok, I saw 0day bot also started to report those which is good. For example, lkml.org/lkml/2020/5/12/1358 which so far is nit blocking 0day on linux-next since it does not use panic_on_warn yet (while syzbot does). Thus, I am more convinced that we should not revert the commit just for syzbot until someone could also convince 0day to select RCU_EXPERT and then DEBUG_RCU_LIST?
Re: Default enable RCU list lockdep debugging with PROVE_RCU
On Thu, May 14, 2020 at 11:46:23AM -0400, Qian Cai wrote:
>
>
> > On May 14, 2020, at 11:34 AM, Paul E. McKenney wrote:
> >
> > On Thu, May 14, 2020 at 10:03:21AM -0400, Qian Cai wrote:
> >>
> >>
> >>> On May 14, 2020, at 9:54 AM, Paul E. McKenney 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
> >>>>> wrote:
> >>>>>
> >>>>> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
> >>>>>>
> >>>>>>
> >>>>>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell
> >>>>>>> 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. ;-)
>
> I am trying to not getting into a game of carrying any custom patch myself.
>
> Let’s see what syzbot guys will say, and then I’ll enable RCU_EXPERT myself
> if needed, but again we probably never see PROVE_RCU_LIST to be used again in
> syzbot for this path. I surely have no cycles to expand the testing coverage
> for more subsystems at the moment.
Fair enough! And yes, the Linux kernel is quite large, so I certainly am
not asking you to test the whole thing yourself.
Thanx, Paul
Re: Default enable RCU list lockdep debugging with PROVE_RCU
> On May 14, 2020, at 11:34 AM, Paul E. McKenney wrote:
>
> On Thu, May 14, 2020 at 10:03:21AM -0400, Qian Cai wrote:
>>
>>
>>> On May 14, 2020, at 9:54 AM, Paul E. McKenney 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 wrote:
>>>>>
>>>>> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
>>>>>>
>>>>>>
>>>>>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell
>>>>>>> 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. ;-)
I am trying to not getting into a game of carrying any custom patch myself.
Let’s see what syzbot guys will say, and then I’ll enable RCU_EXPERT myself if
needed, but again we probably never see PROVE_RCU_LIST to be used again in
syzbot for this path. I surely have no cycles to expand the testing coverage
for more subsystems at the moment.
Re: Default enable RCU list lockdep debugging with PROVE_RCU
On Thu, May 14, 2020 at 10:03:21AM -0400, Qian Cai wrote:
>
>
> > On May 14, 2020, at 9:54 AM, Paul E. McKenney 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 wrote:
> >>>
> >>> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
> >>>>
> >>>>
> >>>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell
> >>>>> 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
Re: Default enable RCU list lockdep debugging with PROVE_RCU
> On May 14, 2020, at 9:54 AM, Paul E. McKenney 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 wrote:
>>>
>>> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
>>>>
>>>>
>>>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell
>>>>> 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.
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.
Re: Default enable RCU list lockdep debugging with PROVE_RCU
On Thu, May 14, 2020 at 09:44:28AM -0400, Qian Cai wrote:
>
>
> > On May 14, 2020, at 9:33 AM, Paul E. McKenney wrote:
> >
> > On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
> >>
> >>
> >>> On May 14, 2020, at 8:25 AM, Stephen Rothwell
> >>> 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?
Thanx, Paul
Re: Default enable RCU list lockdep debugging with PROVE_RCU
> On May 14, 2020, at 9:33 AM, Paul E. McKenney wrote:
>
> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
>>
>>
>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell 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?
Re: Default enable RCU list lockdep debugging with PROVE_RCU
> On May 14, 2020, at 9:33 AM, Paul E. McKenney wrote:
>
> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
>>
>>
>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell 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?
Yes, if there is a way to enable PROVE_RCU_LIST=y manually, that is fine. I
think we would want to make it easier to enable it. Currently, it is buried
into RCU_EXPERT?
Re: Default enable RCU list lockdep debugging with PROVE_RCU
On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote:
>
>
> > On May 14, 2020, at 8:25 AM, Stephen Rothwell 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?
Thanx, Paul
Re: Default enable RCU list lockdep debugging with PROVE_RCU
> On May 14, 2020, at 8:25 AM, Stephen Rothwell 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.
Re: Default enable RCU list lockdep debugging with PROVE_RCU
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)?
--
Cheers,
Stephen Rothwell
pgp562Umi5Bp7.pgp
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