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From: Nick Desaulniers <ndesaulniers@google.com>
To: Marco Elver <elver@google.com>
Cc: george.burgess.iv@gmail.com,
	Kan Liang <kan.liang@linux.intel.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	kasan-dev <kasan-dev@googlegroups.com>,
	kernel test robot <rong.a.chen@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>, LKP <lkp@lists.01.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [rcu] 2f08469563: BUG:kernel_reboot-without-warning_in_boot_stage
Date: Wed, 20 May 2020 09:32:43 -0700	[thread overview]
Message-ID: <CAKwvOd=ga4cjJCQASVH=Vwjkk5_Qh7b_TtoTSBBoLiMENL8hOQ@mail.gmail.com> (raw)
In-Reply-To: <CANpmjNOeXmD5E3O50Z3MjkiuCYaYOPyi+1rq=GZvEKwBvLR0Ug@mail.gmail.com>

On Tue, May 19, 2020 at 11:32 AM Marco Elver <elver@google.com> wrote:
>
> This fixes the problem:
> https://lkml.kernel.org/r/20200519182459.87166-1-elver@google.com
>
> I suppose there are several things that happened that caused the above
> bisected changes to trigger this. Hard to say how exactly the above
> bisected changes caused this to manifest, because during early boot
> (while uninitialized) KASAN may just randomly enter kasan_report()
> before the branch (annotated with likely(), which is caught by the
> branch tracer) prevents it from actually generating a report. However,
> if it goes branch tracer -> KASAN -> branch tracers -> KASAN ..., then
> we crash. If I had to guess some combination of different code gen,
> different stack and/or data usage. So all the above bisected changes
> (AFAIK) were red herrings. :-)

Thanks for chasing to resolution.  Consider using a variable to store
a list of flags, as that code (before your patch) invokes the compiler
multiple times to answer the same question.
-- 
Thanks,
~Nick Desaulniers

WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com>
To: lkp@lists.01.org
Subject: Re: [rcu] 2f08469563: BUG:kernel_reboot-without-warning_in_boot_stage
Date: Wed, 20 May 2020 09:32:43 -0700	[thread overview]
Message-ID: <CAKwvOd=ga4cjJCQASVH=Vwjkk5_Qh7b_TtoTSBBoLiMENL8hOQ@mail.gmail.com> (raw)
In-Reply-To: <CANpmjNOeXmD5E3O50Z3MjkiuCYaYOPyi+1rq=GZvEKwBvLR0Ug@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 1078 bytes --]

On Tue, May 19, 2020 at 11:32 AM Marco Elver <elver@google.com> wrote:
>
> This fixes the problem:
> https://lkml.kernel.org/r/20200519182459.87166-1-elver(a)google.com
>
> I suppose there are several things that happened that caused the above
> bisected changes to trigger this. Hard to say how exactly the above
> bisected changes caused this to manifest, because during early boot
> (while uninitialized) KASAN may just randomly enter kasan_report()
> before the branch (annotated with likely(), which is caught by the
> branch tracer) prevents it from actually generating a report. However,
> if it goes branch tracer -> KASAN -> branch tracers -> KASAN ..., then
> we crash. If I had to guess some combination of different code gen,
> different stack and/or data usage. So all the above bisected changes
> (AFAIK) were red herrings. :-)

Thanks for chasing to resolution.  Consider using a variable to store
a list of flags, as that code (before your patch) invokes the compiler
multiple times to answer the same question.
-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2020-05-20 16:32 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-17  1:17 [rcu] 2f08469563: BUG:kernel_reboot-without-warning_in_boot_stage kernel test robot
2020-05-17  1:17 ` kernel test robot
2020-05-17  3:47 ` Paul E. McKenney
2020-05-17  3:47   ` Paul E. McKenney
2020-05-18 10:11   ` Marco Elver
2020-05-18 10:11     ` Marco Elver
2020-05-18 12:44     ` Marco Elver
2020-05-18 12:44       ` Marco Elver
2020-05-18 14:34       ` Marco Elver
2020-05-18 14:34         ` Marco Elver
2020-05-18 17:49         ` Nick Desaulniers
2020-05-18 17:49           ` Nick Desaulniers
2020-05-18 18:05           ` Marco Elver
2020-05-18 18:05             ` Marco Elver
2020-05-19 10:16             ` Marco Elver
2020-05-19 10:16               ` Marco Elver
2020-05-19 13:40               ` Marco Elver
2020-05-19 13:40                 ` Marco Elver
2020-05-19 18:32                 ` Marco Elver
2020-05-19 18:32                   ` Marco Elver
2020-05-20 16:32                   ` Nick Desaulniers [this message]
2020-05-20 16:32                     ` Nick Desaulniers

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