Messages in this thread | | | Date | Wed, 26 Aug 2009 14:35:52 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 08/12] add trace events for each syscall entry/exit |
| |
On Tue, Aug 25, 2009 at 06:02:37PM +0200, Hendrik Brueckner wrote: > On Tue, Aug 25, 2009 at 04:15:49PM +0200, Frederic Weisbecker wrote: > > On Tue, Aug 25, 2009 at 02:50:27PM +0200, Hendrik Brueckner wrote: > > > There are at least two scenarios where syscall_get_nr() can return -1: > > > > > > 1. For example, ptrace stores an invalid syscall number, and thus, > > > tracing code resets it. > > > (see do_syscall_trace_enter in arch/s390/kernel/ptrace.c) > > > > > > 2. The syscall_regfunc() (kernel/tracepoint.c) sets the TIF_SYSCALL_FTRACE > > > (now: TIF_SYSCALL_TRACEPOINT) flag for all threads which includes > > > kernel threads. > > > However, the ftrace selftest triggers a kernel oops when testing syscall > > > trace points: > > > - The kernel thread is started as ususal (do_fork()), > > > - tracing code sets TIF_SYSCALL_FTRACE, > > > - the ret_from_fork() function is triggered and starts > > > ftrace_syscall_exit() with an invalid syscall number. > > > > > > > > I wonder if there is any way to identify such situation...? > For the second case, it might be an option to avoid setting the > TIF_SYSCALL_FTRACE flag for kernel threads. > > Kernel threads have task_struct->mm set to NULL. > (Thanks to Heiko for that hint ;-) > > The idea is then to check the mm field in syscall_regfunc() and > set the flag accordingly. > > However, I think the patch is an optional add-on becase checking > the syscall number is still required for case 1). > > --- > kernel/tracepoint.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > --- a/kernel/tracepoint.c > +++ b/kernel/tracepoint.c > @@ -593,7 +593,9 @@ void syscall_regfunc(void) > if (!sys_tracepoint_refcount) { > read_lock_irqsave(&tasklist_lock, flags); > do_each_thread(g, t) { > - set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE); > + /* Skip kernel threads. */ > + if (t->mm) > + set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE); > } while_each_thread(g, t); > read_unlock_irqrestore(&tasklist_lock, flags); > } >
Yeah, and as told before, syscalls tracing from kernel thread is an interesting point but we can't do it that way.
I'm queuing this patch for .32, but I need you Signed-off-by to apply it :)
Thanks.
| |