On Sun, 6 Dec 2015 10:02:56 +0800 Li Bin <huawei.li...@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: Benjamin Herrenschmidt <b...@kernel.crashing.org> > Cc: Paul Mackerras <pau...@samba.org> > Cc: Michael Ellerman <m...@ellerman.id.au> > Cc: linuxppc-dev@lists.ozlabs.org > Suggested-by: Steven Rostedt <rost...@goodmis.org> > Signed-off-by: Li Bin <huawei.li...@huawei.com> Hi, can I get a POWERPC maintainer to ack this, or you can take it too. -- Steve > --- > arch/powerpc/kernel/ftrace.c | 12 +++++------- > 1 files changed, 5 insertions(+), 7 deletions(-) > > diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c > index 44d4d8e..83e3c88 100644 > --- a/arch/powerpc/kernel/ftrace.c > +++ b/arch/powerpc/kernel/ftrace.c > @@ -47,13 +47,11 @@ ftrace_modify_code(unsigned long ip, unsigned int old, > unsigned int new) > unsigned int replaced; > > /* > - * Note: Due to modules and __init, code can > - * disappear and change, we need to protect against faulting > - * as well as code changing. We do this by using the > - * probe_kernel_* functions. > - * > - * No real locking needed, this code is run through > - * kstop_machine, or before SMP starts. > + * 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 */ _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
