Re: [regression drm/noveau] suspend to ram -> BOOM: exception RIP: drm_calc_vbltimestamp_from_scanoutpos+335

[Mike Galbraith <efault@gmx.de>]

[-- Attachment #1: Type: text/plain, Size: 3288 bytes --]

On Wed, 2017-07-12 at 07:37 -0400, Ilia Mirkin wrote:
> On Wed, Jul 12, 2017 at 7:25 AM, Mike Galbraith <efault@gmx.de> wrote:
> > On Wed, 2017-07-12 at 11:55 +0200, Mike Galbraith wrote:
> >> On Tue, 2017-07-11 at 14:22 -0400, Ilia Mirkin wrote:
> >> >
> >> > Some display stuff did change for 4.13 for GM20x+ boards. If it's not
> >> > too much trouble, a bisect would be pretty useful.
> >>
> >> Bisection seemingly went fine, but the result is odd.
> >>
> >> e98c58e55f68f8785aebfab1f8c9a03d8de0afe1 is the first bad commit
> >
> > But it really really is bad.  Looking at gitk fork in the road leading
> > to it...
> >
> > 52d9d38c183b drm/sti:fix spelling mistake: "compoment" -> "component" - good
> > e4e818cc2d7c drm: make drm_panel.h self-contained                     - good
> > 9cf8f5802f39 drm: add missing declaration to drm_blend.h              - good
> >
> > Before the git highway splits, all is well.  The lane with commits
> > works fine at both ends, but e98c58e55f68 is busted.  Merge arfifact?
> 
> Hmmm... that tree does not appear to have gotten a v4.12 backmerge at
> any point. The last backmerge from Linus as far as I can tell was
> v4.11-rc7. Could be an interaction with some out-of-tree change.

Ok, a network outage gave me time to go hunting.  Indeed it is a bad
interaction with the tree DRM merged into.  All DRM did was to slip a
WARN_ON_ONCE() that nouveau triggers into a kernel module where such
things no longer warn, they blow the box out of the water.  I made a
dinky testcase module (attached), and bisected to the real root....

19d436268dde95389c616bb3819da73f0a8b28a8 is the first bad commit
commit 19d436268dde95389c616bb3819da73f0a8b28a8
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Sat Feb 25 08:56:53 2017 +0100

    debug: Add _ONCE() logic to report_bug()
    
    Josh suggested moving the _ONCE logic inside the trap handler, using a
    bit in the bug_entry::flags field, avoiding the need for the extra
    variable.
    
    Sadly this only works for WARN_ON_ONCE(), since the others have
    printk() statements prior to triggering the trap.
    
    Still, this saves a fair amount of text and some data:
    
      text         data       filename
      10682460     4530992    defconfig-build/vmlinux.orig
      10665111     4530096    defconfig-build/vmlinux.patched
    
    Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>

:040000 040000 9f47f66ec4c234f6ee8e2a09e991c95fe47cf2c1 3e92aa9e77b39ed075ae2c3bdf041d92ef898f62 M	arch
:040000 040000 34f70b73d40c82533dd7df9b289106be69e2fa8d dd5d7248694a36b3e170f2dca5d9c4121535a990 M	include
:040000 040000 f6e627b0d378f0a00d2987fdd0c7b215306e6e3c b360d4ee2579744cce530184d7dab13493f73ee0 M	lib 

[-- Attachment #2: warn_on_once.patch --]
[-- Type: text/x-patch, Size: 675 bytes --]

---
 kernel/Makefile |    2 ++
 kernel/foo.c    |   15 +++++++++++++++
 2 files changed, 17 insertions(+)

--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -111,6 +111,8 @@ obj-$(CONFIG_MEMBARRIER) += membarrier.o
 
 obj-$(CONFIG_HAS_IOMEM) += memremap.o
 
+obj-m += foo.o
+
 $(obj)/configs.o: $(obj)/config_data.h
 
 targets += config_data.gz
--- /dev/null
+++ b/kernel/foo.c
@@ -0,0 +1,15 @@
+#include <linux/module.h>
+#include <linux/bug.h>
+
+static int __init foo_init(void)
+{
+	printk(KERN_INFO "foo: module loaded\n");
+	WARN_ON_ONCE(1);
+	return 0;
+}
+
+static void __exit foo_exit(void) { }
+
+module_init(foo_init);
+module_exit(foo_exit);
+MODULE_LICENSE("GPL");