linux-kernel - Re: [PATCH] cpumask: Omit terminating null byte in cpumap_print_{list,bitmask}_to

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Date:   Sun, 19 Sep 2021 09:52:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Barry Song <21cnbao@...il.com>
Cc:     Tobias Klauser <tklauser@...tanz.ch>,
        Yury Norov <yury.norov@...il.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        "tiantao (H)" <tiantao6@...ilicon.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpumask: Omit terminating null byte in
 cpumap_print_{list,bitmask}_to_buf

On Sun, Sep 19, 2021 at 07:33:52PM +1200, Barry Song wrote:
> On Sat, Sep 18, 2021 at 1:27 AM Tobias Klauser <tklauser@...tanz.ch> wrote:
> >
> > On 2021-09-17 at 01:19:04 +0200, Yury Norov <yury.norov@...il.com> wrote:
> > > [CC Greg KH <gregkh@...uxfoundation.org>]
> > >
> > > On Thu, Sep 16, 2021 at 10:53:39PM +0000, Song Bao Hua (Barry Song) wrote:
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Tobias Klauser [mailto:tklauser@...tanz.ch]
> > > > > Sent: Friday, September 17, 2021 10:27 AM
> > > > > To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Jonathan Cameron
> > > > > <jonathan.cameron@...wei.com>; tiantao (H) <tiantao6@...ilicon.com>; Song Bao
> > > > > Hua (Barry Song) <song.bao.hua@...ilicon.com>
> > > > > Cc: Andrew Morton <akpm@...ux-foundation.org>; Andy Shevchenko
> > > > > <andriy.shevchenko@...ux.intel.com>; Yury Norov <yury.norov@...il.com>; Peter
> > > > > Zijlstra <peterz@...radead.org>; linux-kernel@...r.kernel.org
> > > > > Subject: [PATCH] cpumask: Omit terminating null byte in
> > > > > cpumap_print_{list,bitmask}_to_buf
> > > > >
> > > > > The changes in the patch series [1] introduced a terminating null byte
> > > > > when reading from cpulist or cpumap sysfs files, for example:
> > > > >
> > > > >   $ xxd /sys/devices/system/node/node0/cpulist
> > > > >   00000000: 302d 310a 00                             0-1..
> > > > >
> > > > > Before this change, the output looked as follows:
> > > > >
> > > > >   $ xxd /sys/devices/system/node/node0/cpulist
> > > > >   00000000: 302d 310a                                0-1.
> > > >
> > > > If we don't use xxd, I don't see any actual harm of this NULL byte
> > > > by cat, lscpu, numactl etc. this doesn't break them at all.
> > >
> > > Barry, Tobias' script that uses xxd is userspace. Linux kernel never breaks
> > > userspace.
> >
> > FWIW, the example using xxd was just to illustrate the issue in a
> > concise way for the commit message. This is breaking other userspace
> > programs as well. Originally, I discovered this because Kubernetes'
> > kubelet was crashing on a bpf-next kernel. See [1] and following
> > comments for more information:
> >
> > [1] https://github.com/cilium/cilium/pull/17394#issuecomment-920902042
> >
> 
> cat, lscpu, numactl tools were tested. the above was not in the test cases.
> Anyway, if some apps depend on the last character, this patch makes
> sense. we need this one. sorry for missing the test case.
> 
> Acked-by: Barry Song <song.bao.hua@...ilicon.com>
> 
> Greg, can you please help merge this one into 5.15?

Yes, will apply it to my tree soon.

thanks,

greg k-h