linux-kernel - Re: [PATCH v18 4/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page

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: <68bc8cc9-a15b-2e97-9a2a-282fe6e9bd3f@oracle.com>
Date:   Wed, 10 Mar 2021 14:10:12 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     paulmck@...nel.org, Michal Hocko <mhocko@...e.com>
Cc:     Muchun Song <songmuchun@...edance.com>, corbet@....net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org,
        osalvador@...e.de, song.bao.hua@...ilicon.com, david@...hat.com,
        naoya.horiguchi@....com, joao.m.martins@...cle.com,
        duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, Chen Huang <chenhuang5@...wei.com>,
        Bodeddula Balasubramaniam <bodeddub@...zon.com>
Subject: Re: [PATCH v18 4/9] mm: hugetlb: alloc the vmemmap pages associated
 with each HugeTLB page

On 3/10/21 1:49 PM, Paul E. McKenney wrote:
> On Wed, Mar 10, 2021 at 10:11:22PM +0100, Michal Hocko wrote:
>> On Wed 10-03-21 10:56:08, Mike Kravetz wrote:
>>> On 3/10/21 7:19 AM, Michal Hocko wrote:
>>>> On Mon 08-03-21 18:28:02, Muchun Song wrote:
>>>> [...]
>>>>> @@ -1447,7 +1486,7 @@ void free_huge_page(struct page *page)
>>>>>  	/*
>>>>>  	 * Defer freeing if in non-task context to avoid hugetlb_lock deadlock.
>>>>>  	 */
>>>>> -	if (!in_task()) {
>>>>> +	if (in_atomic()) {
>>>>
>>>> As I've said elsewhere in_atomic doesn't work for CONFIG_PREEMPT_COUNT=n.
>>>> We need this change for other reasons and so it would be better to pull
>>>> it out into a separate patch which also makes HUGETLB depend on
>>>> PREEMPT_COUNT.
>>>
>>> Yes, the issue of calling put_page for hugetlb pages from any context
>>> still needs work.  IMO, that is outside the scope of this series.  We
>>> already have code in this path which blocks/sleeps.
>>>
>>> Making HUGETLB depend on PREEMPT_COUNT is too restrictive.  IIUC,
>>> PREEMPT_COUNT will only be enabled if we enable:
>>> PREEMPT "Preemptible Kernel (Low-Latency Desktop)"
>>> PREEMPT_RT "Fully Preemptible Kernel (Real-Time)"
>>> or, other 'debug' options.  These are not enabled in 'more common'
>>> kernels.  Of course, we do not want to disable HUGETLB in common
>>> configurations.
>>
>> I haven't tried that but PREEMPT_COUNT should be selectable even without
>> any change to the preemption model (e.g. !PREEMPT).
> 
> It works reliably for me, for example as in the diff below.  So,
> as Michal says, you should be able to add "select PREEMPT_COUNT" to
> whatever Kconfig option you need to.
> 

Thanks Paul.

I may have been misreading Michal's suggestion of "make HUGETLB depend on
PREEMPT_COUNT".  We could "select PREEMPT_COUNT" if HUGETLB is enabled.
However, since HUGETLB is enabled in most configs, then this would
result in PREEMPT_COUNT also being enabled in most configs.  I honestly
do not know how much this will cost us?  I assume that if it was free or
really cheap it would already be always on?

-- 
Mike Kravetz

> 							Thanx, Paul
> 
> diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> index 3128b7c..7d9f989 100644
> --- a/kernel/rcu/Kconfig
> +++ b/kernel/rcu/Kconfig
> @@ -8,6 +8,7 @@ menu "RCU Subsystem"
>  config TREE_RCU
>  	bool
>  	default y if SMP
> +	select PREEMPT_COUNT
>  	help
>  	  This option selects the RCU implementation that is
>  	  designed for very large SMP system with hundreds or
>