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Date: Thu, 2 Nov 2017 10:16:49 -0400 From: Pavel Tatashin <pasha.tatashin@...cle.com> To: Michal Hocko <mhocko@...nel.org> Cc: steven.sistare@...cle.com, daniel.m.jordan@...cle.com, akpm@...ux-foundation.org, mgorman@...hsingularity.net, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v1 1/1] mm: buddy page accessed before initialized >>>> Now, that memory is not zeroed, page_is_buddy() can return true after kexec >>>> when memory is dirty (unfortunately memset(1) with CONFIG_VM_DEBUG does not >>>> catch this case). And proceed further to incorrectly remove buddy from the >>>> list. >>> >>> OK, I thought this was a regression from one of the recent patches. So >>> the problem is not new. Why don't we see the same problem during the >>> standard boot? >> >> Because, I believe, BIOS is zeroing all the memory for us. > > I thought you were runnning with the debugging which poisons all the > allocated memory... Yes, but as I said, unfortunately memset(1) with CONFIG_VM_DEBUG does not catch this case. So, when CONFIG_VM_DEBUG is enabled kexec reboots without issues. > >>>> This is why we must initialize the computed buddy page beforehand. >>> >>> Ble, this is really ugly. I will think about it more. >>> >> >> Another approach that I considered is to split loop inside >> deferred_init_range() into two loops: one where we initialize pages by >> calling __init_single_page(), another where we free them to buddy allocator >> by calling deferred_free_range(). > > Yes, that would make much more sense to me. > Ok, so should I submit a new patch with two loops? (The logic within loops is going to be the same: if (!pfn_valid_within(pfn)) { } else if (!(pfn & nr_pgmask) && !pfn_valid(pfn)) { } else if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) { } else if (page && (pfn & nr_pgmask)) { This fix was already added into mm-tree as mm-deferred_init_memmap-improvements-fix-2.patch Thank you, Pasha
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