From: James Hogan <james.hogan@imgtec.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Li Bin <huawei.libin@huawei.com>,
mingo@redhat.com, linux-kernel@vger.kernel.org,
linux-metag@vger.kernel.org
Subject: Re: [PATCH v2 2/5] metag: ftrace: fix the comments for ftrace_modify_code
Date: Wed, 23 Dec 2015 17:39:05 +0000 [thread overview]
Message-ID: <20151223173905.GA22683@jhogan-linux.le.imgtec.org> (raw)
In-Reply-To: <20151223123346.46bb525b@gandalf.local.home>
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Hi Steven,
On Wed, Dec 23, 2015 at 12:33:46PM -0500, Steven Rostedt wrote:
> On Sun, 6 Dec 2015 10:02:55 +0800
> Li Bin <huawei.libin@huawei.com> wrote:
>
> > There is no need to worry about module and __init text disappearing
> > case, because that ftrace has a module notifier that is called when
> > a module is being unloaded and before the text goes away and this
> > code grabs the ftrace_lock mutex and removes the module functions
> > from the ftrace list, such that it will no longer do any
> > modifications to that module's text, the update to make functions
> > be traced or not is done under the ftrace_lock mutex as well.
> > And by now, __init section codes should not been modified
> > by ftrace, because it is black listed in recordmcount.c and
> > ignored by ftrace.
> >
> > Cc: James Hogan <james.hogan@imgtec.com>
> > Cc: linux-metag@vger.kernel.org
> > Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> > Signed-off-by: Li Bin <huawei.libin@huawei.com>
>
> Hi, can I get a metag maintainer to ack this. Or you can take the patch
> too.
Yep, sorry for the delay,
Acked-by: James Hogan <james.hogan@imgtec.com>
Cheers
James
>
> -- Steve
>
> > ---
> > arch/metag/kernel/ftrace.c | 11 +++++------
> > 1 files changed, 5 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/metag/kernel/ftrace.c b/arch/metag/kernel/ftrace.c
> > index ed1d685..ac8c039 100644
> > --- a/arch/metag/kernel/ftrace.c
> > +++ b/arch/metag/kernel/ftrace.c
> > @@ -54,12 +54,11 @@ static int ftrace_modify_code(unsigned long pc, unsigned char *old_code,
> > unsigned char replaced[MCOUNT_INSN_SIZE];
> >
> > /*
> > - * Note: Due to modules and __init, code can
> > - * disappear and change, we need to protect against faulting
> > - * as well as code changing.
> > - *
> > - * No real locking needed, this code is run through
> > - * kstop_machine.
> > + * Note:
> > + * We are paranoid about modifying text, as if a bug was to happen, it
> > + * could cause us to read or write to someplace that could cause harm.
> > + * Carefully read and modify the code with probe_kernel_*(), and make
> > + * sure what we read is what we expected it to be before modifying it.
> > */
> >
> > /* read the text we want to modify */
>
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prev parent reply other threads:[~2015-12-23 17:39 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-06 2:02 [PATCH v2 0/5] ftrace: fix ftrace misleading comments for arch using it Li Bin
[not found] ` <1449367378-29430-1-git-send-email-huawei.libin-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2015-12-06 2:02 ` [PATCH v2 2/5] metag: ftrace: fix the comments for ftrace_modify_code Li Bin
2015-12-23 17:33 ` Steven Rostedt
2015-12-23 17:39 ` James Hogan [this message]
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