linux-kernel - Re: [PATCH] mm/hugetlb: avoid get wrong ptep caused by race

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Date:   Tue, 18 Feb 2020 16:51:53 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        "Longpeng (Mike)" <longpeng2@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, arei.gonglei@...wei.com,
        weidong.huang@...wei.com, weifuqiang@...wei.com,
        kvm@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: avoid get wrong ptep caused by race

On 2/18/20 12:37 PM, Sean Christopherson wrote:
> On Tue, Feb 18, 2020 at 08:10:25PM +0800, Longpeng(Mike) wrote:
>> Our machine encountered a panic after run for a long time and
>> the calltrace is:
> 
> What's the actual panic?  Is it a BUG() in hugetlb_fault(), a bad pointer
> dereference, etc...?

I too would like some more information on the panic.
If your analysis is correct, then I would expect the 'ptep' returned by
huge_pte_offset() to not point to a pte but rather some random address.
This is because the 'pmd' calculated by pmd_offset(pud, addr) is not
really the address of a pmd.  So, perhaps there is an addressing exception
at huge_ptep_get() near the beginning of hugetlb_fault()?

	ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
	if (ptep) {
		entry = huge_ptep_get(ptep);
		...

-- 
Mike Kravetz