From: Pavel Tatashin <pasha.tatashin@oracle.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
akpm@linux-foundation.org, mgorman@techsingularity.net,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/1] mm: buddy page accessed before initialized
Date: Thu, 2 Nov 2017 10:16:49 -0400 [thread overview]
Message-ID: <813ed7e3-9347-a1f2-1629-464d920f877d@oracle.com> (raw)
In-Reply-To: <20171102140830.z5uqmrurb6ohfvlj@dhcp22.suse.cz>
>>>> 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
next prev parent reply other threads:[~2017-11-02 14:17 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 15:50 [PATCH v1 0/1] buddy page accessed before initialized Pavel Tatashin
2017-10-31 15:50 ` [PATCH v1 1/1] mm: " Pavel Tatashin
2017-11-02 13:32 ` Michal Hocko
2017-11-02 13:39 ` Pavel Tatashin
2017-11-02 13:54 ` Michal Hocko
2017-11-02 14:00 ` Pavel Tatashin
2017-11-02 14:08 ` Michal Hocko
2017-11-02 14:16 ` Pavel Tatashin [this message]
2017-11-02 14:27 ` Michal Hocko
2017-11-02 16:10 ` Pavel Tatashin
2017-11-03 8:59 ` Michal Hocko
2017-11-03 14:17 ` Pavel Tatashin
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