From: "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>
To: Dave Hansen <dave.hansen@intel.com>,
"tiantao (H)" <tiantao6@hisilicon.com>,
"corbet@lwn.net" <corbet@lwn.net>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Cc: "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"Valentin Schneider" <valentin.schneider@arm.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: RE: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue of sysfs pagebuf
Date: Thu, 29 Apr 2021 21:08:50 +0000 [thread overview]
Message-ID: <602918a1e2214ea7bd0890a751975566@hisilicon.com> (raw)
In-Reply-To: <146e051b-603c-a6d3-43d8-d083cf2c8119@intel.com>
> -----Original Message-----
> From: Dave Hansen [mailto:dave.hansen@intel.com]
> Sent: Friday, April 30, 2021 2:21 AM
> To: tiantao (H) <tiantao6@hisilicon.com>; corbet@lwn.net;
> gregkh@linuxfoundation.org; Song Bao Hua (Barry Song)
> <song.bao.hua@hisilicon.com>
> Cc: linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org; Rafael J.
> Wysocki <rafael@kernel.org>; Peter Zijlstra <peterz@infradead.org>; Valentin
> Schneider <valentin.schneider@arm.com>; Dave Hansen
> <dave.hansen@linux.intel.com>; Daniel Bristot de Oliveira <bristot@redhat.com>
> Subject: Re: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue
> of sysfs pagebuf
>
> On 4/29/21 12:03 AM, Tian Tao wrote:
> > diff --git a/Documentation/ABI/stable/sysfs-devices-node
> b/Documentation/ABI/stable/sysfs-devices-node
> > index 484fc04..82dfe64 100644
> > --- a/Documentation/ABI/stable/sysfs-devices-node
> > +++ b/Documentation/ABI/stable/sysfs-devices-node
> > @@ -47,7 +47,10 @@ What: /sys/devices/system/node/nodeX/cpulist
> > Date: October 2002
> > Contact: Linux Memory Management list <linux-mm@kvack.org>
> > Description:
> > - The CPUs associated to the node.
> > + The CPUs associated to the node. The format is like 0-3,
> > + 8-11, 14,17. maximum size is PAGE_SIZE, so the tail
> > + of the string will be trimmed while its size is larger
> > + than PAGE_SIZE.
>
> I think it's pretty arguable that truncating output on a real system is
> an ABI break. Doing this would make the interface rather useless.
>
> Don't we need a real solution rather than throwing up our hands?
>
> Do we think >PAGE_SIZE data out of a sysfs file is a worse ABI break or
> something?
This kind of cpu list ABIs have been there for many years but have
never been documented well.
We have two ABIs:
xxx_cpus - in format like 3333333333
xxx_cpus_list - in format like 0,3,5,7,9,11,13....
xxx_cpus_list is another human-readable version of xxx_cpus. It doesn't
include any more useful information than xxx_cpus.
xxx_cpus won't overflow based on BUILD_BUG_ON and maximum NR_CPUS
in kconfig nowadays.
if people all agree the trimmed list is a break of ABI, I think we may
totally remove this list. For these days, this list probably has never
overflowed but literally this could happen.
thoughts?
Thanks
Barry
next prev parent reply other threads:[~2021-04-29 21:08 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 7:03 [PATCH 0/2] clarify and cleanup CPU and NUMA topology ABIs Tian Tao
2021-04-29 7:03 ` [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue of sysfs pagebuf Tian Tao
2021-04-29 14:21 ` Dave Hansen
2021-04-29 15:46 ` Greg KH
2021-04-29 21:08 ` Song Bao Hua (Barry Song) [this message]
2021-04-29 21:38 ` Dave Hansen
2021-04-29 22:32 ` Song Bao Hua (Barry Song)
2021-04-29 22:38 ` Dave Hansen
2021-04-29 22:48 ` Song Bao Hua (Barry Song)
2021-04-30 6:05 ` gregkh
2021-07-23 11:20 ` Song Bao Hua (Barry Song)
2021-07-23 11:28 ` gregkh
2021-07-23 12:48 ` Song Bao Hua (Barry Song)
2021-05-06 23:16 ` kernel test robot
2021-04-29 7:03 ` [PATCH 2/2] Documentation/ABI: Move the topology-related sysfs interface to the right place Tian Tao
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