Messages in this thread | | | Subject | Re: [PATCH] mm: deferred_init_memmap improvements | From | Pasha Tatashin <> | Date | Fri, 6 Oct 2017 09:55:49 -0400 |
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Hi Anshuman,
Thank you very much for looking at this. My reply below::
On 10/06/2017 02:48 AM, Anshuman Khandual wrote: > On 10/04/2017 08:59 PM, Pavel Tatashin wrote: >> This patch fixes another existing issue on systems that have holes in >> zones i.e CONFIG_HOLES_IN_ZONE is defined. >> >> In for_each_mem_pfn_range() we have code like this: >> >> if (!pfn_valid_within(pfn) >> goto free_range; >> >> Note: 'page' is not set to NULL and is not incremented but 'pfn' advances. > > page is initialized to NULL at the beginning of the function.
Yes, it is initialized to NULL but at the beginning of for_each_mem_pfn_range() loop
> PFN advances but we dont proceed unless pfn_valid_within(pfn) > holds true which basically should have checked with arch call > back if the PFN is valid in presence of memory holes as well. > Is not this correct ?
Correct, if pfn_valid_within() is false we jump to the "goto free_range;", which is at the end of for (; pfn < end_pfn; pfn++) loop, so we are not jumping outside of this loop.
> >> Thus means if deferred struct pages are enabled on systems with these kind >> of holes, linux would get memory corruptions. I have fixed this issue by >> defining a new macro that performs all the necessary operations when we >> free the current set of pages. > > If we bail out in case PFN is not valid, then how corruption > can happen ? >
We are not bailing out. We continue next iteration with next pfn, but page is not incremented.
Please let me know if I am missing something.
Thank you, Pasha
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