From: Steven Rostedt <rostedt@goodmis.org>
To: Vincent Donnefort <vdonnefort@google.com>
Cc: Qing Wang <wangqing7171@gmail.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
syzbot+3b5dd2030fe08afdf65d@syzkaller.appspotmail.com,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH] tracing: Fix WARN_ON in tracing_buffers_mmap_close
Date: Fri, 27 Feb 2026 15:56:01 -0500 [thread overview]
Message-ID: <20260227155601.18ebd3ca@gandalf.local.home> (raw)
In-Reply-To: <20260227102038.0fef81e9@gandalf.local.home>
On Fri, 27 Feb 2026 10:20:38 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 27 Feb 2026 11:22:22 +0000
> Vincent Donnefort <vdonnefort@google.com> wrote:
>
> > > Ah right, Syzkaller is using madvise(MADVISE_DOFORK) which resets VM_DONTCOPY.
> >
> > As we are applying restrictive rules for this mapping, I believe setting VM_IO
> > might be a better fix.
>
> Agreed.
>
Adding MM folks so we do this right.
Dear MM folks,
Here's the issue. When the ftrace ring buffer is memory mapped to user
space, we do not want anything "special" done to it. One of those things we
did not want done was to have it copied on fork. To do that, we added
VM_DONTCOPY, but we didn't know that an madvise() could disable that. It
looks like VM_IO will prevent that from happening.
But looking at the various flags, I see there's a VM_SPECIAL. I'm wondering
if that is what we should use?
The effected code is here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/ring_buffer.c#n7172
What's your thoughts?
Thanks,
-- Steve
parent reply other threads:[~2026-02-27 20:55 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <20260227102038.0fef81e9@gandalf.local.home>]
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=20260227155601.18ebd3ca@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-trace-kernel@vger.kernel.org \
--cc=lorenzo.stoakes@oracle.com \
--cc=mathieu.desnoyers@efficios.com \
--cc=mhiramat@kernel.org \
--cc=syzbot+3b5dd2030fe08afdf65d@syzkaller.appspotmail.com \
--cc=vbabka@suse.cz \
--cc=vdonnefort@google.com \
--cc=wangqing7171@gmail.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