Re: PROBLEM: Resume form hibernate broken by setting NX on gap

[Ingo Molnar]

* Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote:

> Hi,
> 
> I have been working on a bug that causes my laptop to freeze during
> resume from hibernation. I did a bisect to find the offending commit:
> 
> [ab76f7b4ab] x86/mm: Set NX on gap between __ex_table and rodata
> 
> There is more information in the bugzilla report [1] that
> I've been working on but I will summarize things below.
> 
> I've experienced intermittent but reproducible freezes when resuming
> from hibernation since about kernel version 3.19. The freeze was
> significantly more reproducible when a few applications were loaded
> before hibernation and would largely not happen if hibernated
> immediately after booting to a desktop. I did some tracing work to find
> that the kernel gets as far as the resume_image call in
> swsusp_arch_resume and I could not find any response from the image
> kernel when I hit the bug. I also did testing that seemed to rule out
> this being caused by a problematic driver.
> 
> I did a successful bisect between 3.18 and 3.19 which found a bug in
> commit f5b2831d6 that was then later fixed by commit 55696b1f66 in 4.4.
> Then, I did a second bisect with a ported version of the fix to the
> first bug and found commit ab76f7b4ab in 4.3 to also break hibernation
> with what appears to be the exact same symptoms. Reverting that commit
> in recent kernels up to and including 4.6 fixes the issue and restores
> reliable hibernation. However, it's not at all clear to me why that
> commit would cause this issue or how to fix the issue without reverting.

I've attached that commit below and also Cc:-ed a few more people who might have 
an idea about why this regressed. Worst-case we'll have to revert it.

Thanks,

	Ingo

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