linux-kernel - Re: [PATCH] hugetlb: detect race if fail to COW

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAONaPpGQdpNDT9EuTq_xian+bRFDUsLn7AgjtG-=y0C6-9fDTQ@mail.gmail.com>
Date:	Fri, 18 Nov 2011 15:16:02 +0100
From:	John Kacur <jkacur@...hat.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <jweiner@...hat.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hugetlb: detect race if fail to COW

On Fri, Nov 18, 2011 at 3:04 PM, Hillf Danton <dhillf@...il.com> wrote:
> In the error path that we fail to allocate new huge page, before try again, we
> have to check race since page_table_lock is re-acquired.
>
> If racing, our job is done.
>
> Signed-off-by: Hillf Danton <dhillf@...il.com>
> ---
>
> --- a/mm/hugetlb.c      Fri Nov 18 21:38:30 2011
> +++ b/mm/hugetlb.c      Fri Nov 18 21:48:15 2011
> @@ -2407,7 +2407,14 @@ retry_avoidcopy:
>                                BUG_ON(page_count(old_page) != 1);
>                                BUG_ON(huge_pte_none(pte));
>                                spin_lock(&mm->page_table_lock);
> -                               goto retry_avoidcopy;
> +                               ptep = huge_pte_offset(mm, address & huge_page_mask(h));
> +                               if (likely(pte_same(huge_ptep_get(ptep), pte)))
> +                                       goto retry_avoidcopy;
> +                               /*
> +                                * race occurs while re-acquiring page_table_lock, and
> +                                * our job is done.
> +                                */
> +                               return 0;
>                        }
>                        WARN_ON_ONCE(1);
>                }


I'm not sure about the veracity of the race condition, but you better
do spin_unlock before you return.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/