From: Matthew Wilcox <willy@infradead.org>
To: Muchun Song <songmuchun@bytedance.com>
Cc: Yunfeng Ye <yeyunfeng@huawei.com>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
wuxu.wu@huawei.com, Hewenliang <hewenliang4@huawei.com>
Subject: Re: [PATCH] mm, slub: place the trace before freeing memory in kmem_cache_free()
Date: Sun, 31 Oct 2021 12:54:04 +0000 [thread overview]
Message-ID: <YX6R7EUdxok8phma@casper.infradead.org> (raw)
In-Reply-To: <CAMZfGtU+wyjD6e0Xm7-toqqfA2tsu8nSUQJsZdC=piZzgq76fw@mail.gmail.com>
On Sat, Oct 30, 2021 at 08:23:12PM +0800, Muchun Song wrote:
> On Sat, Oct 30, 2021 at 6:12 PM Yunfeng Ye <yeyunfeng@huawei.com> wrote:
> >
> > After the memory is freed, it may be allocated by other CPUs and has
> > been recorded by trace. So the timing sequence of the memory tracing is
> > inaccurate.
> >
> > For example, we expect the following timing sequeuce:
> >
> > CPU 0 CPU 1
> >
> > (1) alloc xxxxxx
> > (2) free xxxxxx
> > (3) alloc xxxxxx
> > (4) free xxxxxx
> >
> > However, the following timing sequence may occur:
> >
> > CPU 0 CPU 1
> >
> > (1) alloc xxxxxx
> > (2) alloc xxxxxx
> > (3) free xxxxxx
> > (4) free xxxxxx
> >
> > So place the trace before freeing memory in kmem_cache_free().
>
> Could you tell me what problem you have encountered
> here?
It's confusing to see the memory allocated before it's freed. If you're
unaware of this problem, you might think it was being used after free
because (1) happened a long time ago, so you see (2) immediately followed
by (3) and then see the memory being used.
The patch makes sense to me.
next prev parent reply other threads:[~2021-10-31 12:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-30 10:11 [PATCH] mm, slub: place the trace before freeing memory in kmem_cache_free() Yunfeng Ye
2021-10-30 12:23 ` Muchun Song
2021-10-31 12:54 ` Matthew Wilcox [this message]
2021-11-02 7:03 ` John Hubbard
2021-11-02 8:41 ` Vlastimil Babka
2021-11-02 9:06 ` Yunfeng Ye
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=YX6R7EUdxok8phma@casper.infradead.org \
--to=willy@infradead.org \
--cc=akpm@linux-foundation.org \
--cc=cl@linux.com \
--cc=hewenliang4@huawei.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=penberg@kernel.org \
--cc=rientjes@google.com \
--cc=songmuchun@bytedance.com \
--cc=vbabka@suse.cz \
--cc=wuxu.wu@huawei.com \
--cc=yeyunfeng@huawei.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).