From: David Rientjes <rientjes@google.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Dave Hansen <dave.hansen@intel.com>, Mel Gorman <mgorman@suse.de>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Hillf Danton <hillf.zj@alibaba-inc.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Naoya Horiguchi <nao.horiguchi@gmail.com>
Subject: Re: [PATCH v1] mm: hugetlb: call huge_pte_alloc() only if ptep is null
Date: Mon, 30 Nov 2015 14:10:16 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.10.1511301409380.10460@chino.kir.corp.google.com> (raw)
In-Reply-To: <1448524936-10501-1-git-send-email-n-horiguchi@ah.jp.nec.com>
On Thu, 26 Nov 2015, Naoya Horiguchi wrote:
> Currently at the beginning of hugetlb_fault(), we call huge_pte_offset()
> and check whether the obtained *ptep is a migration/hwpoison entry or not.
> And if not, then we get to call huge_pte_alloc(). This is racy because the
> *ptep could turn into migration/hwpoison entry after the huge_pte_offset()
> check. This race results in BUG_ON in huge_pte_alloc().
>
> We don't have to call huge_pte_alloc() when the huge_pte_offset() returns
> non-NULL, so let's fix this bug with moving the code into else block.
>
> Note that the *ptep could turn into a migration/hwpoison entry after
> this block, but that's not a problem because we have another !pte_present
> check later (we never go into hugetlb_no_page() in that case.)
>
> Fixes: 290408d4a250 ("hugetlb: hugepage migration core")
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: <stable@vger.kernel.org> [2.6.36+]
Acked-by: David Rientjes <rientjes@google.com>
It would be nice to provide a sample of the BUG_ON() output in the commit
message, however, so people can quickly find this if greping for what they
just saw kill their machine.
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next prev parent reply other threads:[~2015-11-30 22:10 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-26 8:02 Naoya Horiguchi
2015-11-26 8:29 ` Hillf Danton
2015-11-30 22:10 ` David Rientjes [this message]
2015-12-01 1:20 ` Mike Kravetz
2015-12-01 1:58 ` Naoya Horiguchi
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