The reason for this is fairly well described in:

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2553b67a1fbe7bf202e4e8070ab0b00d3d3a06a2


Basically we're on a platform that uses different code to print the warning.  Currently I'm looking at whether it's better to pick the kernel change or make the crash-reporting code handle the existing kernel format...

Easy to fix the kernel:

remote:   https://chromium-review.googlesource.com/#/c/chromiumos/third_party/kernel/+/754000 UPSTREAM: lib/bug.c: make panic_on_warn available for all architectures        
remote:   https://chromium-review.googlesource.com/#/c/chromiumos/third_party/kernel/+/754221 UPSTREAM: lib/bug.c: use common WARN helper        

---

Will need someone to test on 3.18 (elm and friends), too.  I uploaded my (totally untested) picks here:

remote:   https://chromium-review.googlesource.com/#/c/chromiumos/third_party/kernel/+/754029 UPSTREAM: lib/bug.c: make panic_on_warn available for all architectures        
remote:   https://chromium-review.googlesource.com/#/c/chromiumos/third_party/kernel/+/754030 UPSTREAM: lib/bug.c: use common WARN helper        

Whoops, bugs were accidentally tagged  bug #781343 .  Doh.  4.4 changes landed.  Hopefully 3.18 can land in the next day or so and then we can request merge since it'd be nice to get proper warning statistics on M63.

Turns out 3.18 patches weren't needed, so just requesting merge for 4.4 patches.  AKA:

remote:   https://chromium-review.googlesource.com/#/c/chromiumos/third_party/kernel/+/754000 UPSTREAM: lib/bug.c: make panic_on_warn available for all architectures        
remote:   https://chromium-review.googlesource.com/#/c/chromiumos/third_party/kernel/+/754221 UPSTREAM: lib/bug.c: use common WARN helper      

This bug requires manual review: M63 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), gkihumba@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/kernel/+/81feef77d3cac8654beee550d3d7805e46350ada

commit 81feef77d3cac8654beee550d3d7805e46350ada
Author: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Mon Nov 06 22:25:51 2017

UPSTREAM: lib/bug.c: make panic_on_warn available for all architectures

Christian Borntraeger reported that panic_on_warn doesn't have any
effect on s390.

The panic_on_warn feature was introduced with 9e3961a09798 ("kernel: add
panic_on_warn").  However it did care only for the case when
WANT_WARN_ON_SLOWPATH is defined.  This is turn is only the case for
architectures which do not have an own __WARN_TAINT defined.

Other architectures which do have __WARN_TAINT defined call report_bug()
for warnings within lib/bug.c which does not call panic() in case
panic_on_warn is set.

Let's simply enable the panic_on_warn feature by adding the same code
like it was added to warn_slowpath_common() in panic.c.

This enables panic_on_warn also for arm64, parisc, powerpc, s390 and sh.

BUG= chromium:781384 
TEST=echo WARNING > /sys/kernel/debug/provoke-crash/DIRECT

Change-Id: I8fdf6490ea439e091054995367472accfb46a66c
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Tested-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
(cherry picked from commit d7b85cab74edef84a9330c476478ba8cd732b6a9)
Reviewed-on: https://chromium-review.googlesource.com/754000
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
(cherry picked from commit 0fd77fcb1a5e785e1f93177dd6785aaa7570908a)
Reviewed-on: https://chromium-review.googlesource.com/755524

[modify] https://crrev.com/81feef77d3cac8654beee550d3d7805e46350ada/lib/bug.c

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/kernel/+/c9a1b15bf57d81760fdead8e0651135be7a293b0

commit c9a1b15bf57d81760fdead8e0651135be7a293b0
Author: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Mon Nov 06 22:26:23 2017

UPSTREAM: lib/bug.c: use common WARN helper

The traceoff_on_warning option doesn't have any effect on s390, powerpc,
arm64, parisc, and sh because there are two different types of WARN
implementations:

1) The above mentioned architectures treat WARN() as a special case of a
   BUG() exception.  They handle warnings in report_bug() in lib/bug.c.

2) All other architectures just call warn_slowpath_*() directly.  Their
   warnings are handled in warn_slowpath_common() in kernel/panic.c.

Support traceoff_on_warning on all architectures and prevent any future
divergence by using a single common function to emit the warning.

Also remove the '()' from '%pS()', because the parentheses look funky:

  [   45.607629] WARNING: at /root/warn_mod/warn_mod.c:17 .init_dummy+0x20/0x40 [warn_mod]()

BUG= chromium:781384 
TEST=echo WARNING > /sys/kernel/debug/provoke-crash/DIRECT

Change-Id: I3babe475d30ed2c5e16aa783a1422f3d5c599e74
Reported-by: Chunyu Hu <chuhu@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Tested-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
(cherry picked from commit 2553b67a1fbe7bf202e4e8070ab0b00d3d3a06a2)
Reviewed-on: https://chromium-review.googlesource.com/754221
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
(cherry picked from commit 89660857d58cec2155474f446455c41a22fd2b50)
Reviewed-on: https://chromium-review.googlesource.com/755525

[modify] https://crrev.com/c9a1b15bf57d81760fdead8e0651135be7a293b0/kernel/panic.c
[modify] https://crrev.com/c9a1b15bf57d81760fdead8e0651135be7a293b0/include/asm-generic/bug.h
[modify] https://crrev.com/c9a1b15bf57d81760fdead8e0651135be7a293b0/lib/bug.c