From: Dave Hansen <dave.hansen@intel.com>
To: Oleg Nesterov <oleg@redhat.com>, Michal Hocko <mhocko@kernel.org>
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>,
pbonzini@redhat.com, akpm@linux-foundation.org,
dan.j.williams@intel.com, gleb@kernel.org, mtosatti@redhat.com,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
stefanha@redhat.com, yuhuang@redhat.com, linux-mm@kvack.org,
ross.zwisler@linux.intel.com
Subject: Re: [PATCH v2] mm, proc: Fix region lost in /proc/self/smaps
Date: Tue, 13 Sep 2016 09:21:18 -0700 [thread overview]
Message-ID: <57D8277E.80505@intel.com> (raw)
In-Reply-To: <20160913145906.GA28037@redhat.com>
On 09/13/2016 07:59 AM, Oleg Nesterov wrote:
> On 09/12, Michal Hocko wrote:
>> > Considering how this all can be tricky and how partial reads can be
>> > confusing and even misleading I am really wondering whether we
>> > should simply document that only full reads will provide a sensible
>> > results.
> I agree. I don't even understand why this was considered as a bug.
> Obviously, m_stop() which drops mmap_sep should not be called, or
> all the threads should be stopped, if you want to trust the result.
There was a mapping at a given address. That mapping did not change, it
was not split, its attributes did not change. But, it didn't show up
when reading smaps. Folks _actually_ noticed this in a test suite
looking for that address range in smaps.
IOW, we had goofy kernel behavior, and it broke a reasonable test
program. The test program just used fgets() to read into a fixed-length
buffer, which is a completely normal thing to do.
To get "sensible results", doesn't userspace have to somehow know in
advance how many bytes of data a given VMA will generate in smaps output?
next prev parent reply other threads:[~2016-09-13 16:21 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-12 3:12 [PATCH v2] mm, proc: Fix region lost in /proc/self/smaps Xiao Guangrong
2016-09-12 12:54 ` Michal Hocko
2016-09-12 15:01 ` Dave Hansen
2016-09-12 19:10 ` Michal Hocko
2016-09-13 3:01 ` Xiao Guangrong
2016-09-13 14:59 ` Oleg Nesterov
2016-09-13 16:21 ` Dave Hansen [this message]
2016-09-14 15:38 ` Oleg Nesterov
2016-09-19 7:21 ` Xiao Guangrong
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=57D8277E.80505@intel.com \
--to=dave.hansen@intel.com \
--cc=akpm@linux-foundation.org \
--cc=dan.j.williams@intel.com \
--cc=gleb@kernel.org \
--cc=guangrong.xiao@linux.intel.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
--cc=mtosatti@redhat.com \
--cc=oleg@redhat.com \
--cc=pbonzini@redhat.com \
--cc=ross.zwisler@linux.intel.com \
--cc=stefanha@redhat.com \
--cc=yuhuang@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).