Re: [PATCH] fprobe: Release rethook after the ftrace_ops is unregistered

[Jiri Olsa]

On Thu, Jun 15, 2023 at 08:59:20AM -0400, Steven Rostedt wrote:
> 
> Masami,
> 
> Want to take this via your probes/urgent branch and send it off to Linus?

hi,
did this one make it into some tree?

thanks,
jirka


> 
> -- Steve
> 
> 
> On Thu, 15 Jun 2023 13:52:36 +0200
> Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> 
> > While running bpf selftests it's possible to get following fault:
> > 
> >   general protection fault, probably for non-canonical address \
> >   0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI
> >   ...
> >   Call Trace:
> >    <TASK>
> >    fprobe_handler+0xc1/0x270
> >    ? __pfx_bpf_testmod_init+0x10/0x10
> >    ? __pfx_bpf_testmod_init+0x10/0x10
> >    ? bpf_fentry_test1+0x5/0x10
> >    ? bpf_fentry_test1+0x5/0x10
> >    ? bpf_testmod_init+0x22/0x80
> >    ? do_one_initcall+0x63/0x2e0
> >    ? rcu_is_watching+0xd/0x40
> >    ? kmalloc_trace+0xaf/0xc0
> >    ? do_init_module+0x60/0x250
> >    ? __do_sys_finit_module+0xac/0x120
> >    ? do_syscall_64+0x37/0x90
> >    ? entry_SYSCALL_64_after_hwframe+0x72/0xdc
> >    </TASK>
> > 
> > In unregister_fprobe function we can't release fp->rethook while it's
> > possible there are some of its users still running on another cpu.
> > 
> > Moving rethook_free call after fp->ops is unregistered with
> > unregister_ftrace_function call.
> > 
> > Fixes: 5b0ab78998e3 ("fprobe: Add exit_handler support")
> > Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> >  kernel/trace/fprobe.c | 12 +++---------
> >  1 file changed, 3 insertions(+), 9 deletions(-)
> > 
> > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> > index 18d36842faf5..0121e8c0d54e 100644
> > --- a/kernel/trace/fprobe.c
> > +++ b/kernel/trace/fprobe.c
> > @@ -364,19 +364,13 @@ int unregister_fprobe(struct fprobe *fp)
> >  		    fp->ops.saved_func != fprobe_kprobe_handler))
> >  		return -EINVAL;
> >  
> > -	/*
> > -	 * rethook_free() starts disabling the rethook, but the rethook handlers
> > -	 * may be running on other processors at this point. To make sure that all
> > -	 * current running handlers are finished, call unregister_ftrace_function()
> > -	 * after this.
> > -	 */
> > -	if (fp->rethook)
> > -		rethook_free(fp->rethook);
> > -
> >  	ret = unregister_ftrace_function(&fp->ops);
> >  	if (ret < 0)
> >  		return ret;
> >  
> > +	if (fp->rethook)
> > +		rethook_free(fp->rethook);
> > +
> >  	ftrace_free_filter(&fp->ops);
> >  
> >  	return ret;
>