Messages in this thread | | | Date | Thu, 28 Jan 2016 09:42:32 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v2] x86/mm: avoid premature success when changing page attributes |
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* Jan Beulich <JBeulich@suse.com> wrote:
> When __change_page_attr() finds it necessary to call > __cpa_process_fault(), it passes its return value directly up to its > own caller, even if this indicates success. Success to the callers, > however, means that whatever ->numpages currently holds is the count > of successfully processed pages. The cases when __change_page_attr() > calls __cpa_process_fault(), otoh, don't generally mean the entire > range got processed (as can be seen from one of the two success return > paths in __cpa_process_fault() adjusting ->numpages). > > When a top level caller, like in the case of change_page_attr_set_clr() > only meaning to alter _PAGE_NX, wants to suppress alias processing, the > boolean value to indicate so results in __cpa_process_fault() taking > its other successful exit path. Since ->numpages so far didn't get > adjusted there, hitting either of the conditions that cause > __cpa_process_fault() to get called meant early termination of the > processing without having processed the entire range, yet still > reporting success. > > Signed-off-by: Jan Beulich <jbeulich@suse.com> > --- > v2: Completely re-written description.
So maybe it's just me, but I'm still quite unhappy about this changelog, it's hard to parse and doesn't really do what a good changelog should do :-/
First I'd like to quote from a mail of Andrew Morton:
"Please update the changelog to describe the current behavior.
Please also describe why you think that behavior should be changed. ie: what's the reason for this patch.
Please update Documentation/ for this feature. Probably that's kernel-parameters.txt for the boot option and sysctl/kernel.txt for the procfs addition."
Alternatively:
1- first describe the symptoms of the bug - how does a user notice?
2- then describe how the code behaves today and how that is causing the bug
3- and then only describe how it's fixed.
Or:
" Current code does (A), this has a problem when (B). We can improve this doing (C), because (D)."
This changelog concentrates excessively on implementational details, without providing context and without touching upon the practical effects - nor does it do a clear before/after description.
I.e. what you describe in the changelog is 90% of what a developer intimate with this code finds interesting about the patch - but that's not what good changelogs are about!
Could we try a v3?
Thanks,
Ingo
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