Messages in this thread Patch in this message | | | Date | Tue, 25 Aug 2009 18:02:37 +0200 | From | Hendrik Brueckner <> | Subject | Re: [PATCH 08/12] add trace events for each syscall entry/exit |
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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); }
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