From cc3b13c11c567c69a6356be98d0c03ff11541d5c Mon Sep 17 00:00:00 2001 From: Hendrik Brueckner Date: Tue, 25 Aug 2009 18:02:37 +0200 Subject: [PATCH] tracing: Don't trace kernel thread syscalls Kernel threads don't call syscalls using the sysenter/sysexit path. Instead they directly call the sys_* or do_* functions that implement the syscalls inside the kernel. The current syscall tracepoints only bind the sysenter/sysexit path, then it has no effect to trace the kernel thread calls to syscalls in that path. Setting the TIF_SYSCALL_TRACEPOINT flag is then useless for these. Actually there is only one case when a kernel thread can reach the usual syscall exit tracing path: when we create a kernel thread, the child comes to ret_from_fork and is the fork() return is then traced. But this information alone is useless, then we don't want to set the TIF flags for these 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. Signed-off-by: Hendrik Brueckner Cc: Jason Baron Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Lai Jiangshan Cc: Steven Rostedt Cc: Peter Zijlstra Cc: Mathieu Desnoyers Cc: Jiaying Zhang Cc: Martin Bligh Cc: Li Zefan Cc: Martin Schwidefsky Cc: Paul Mundt Cc: Heiko Carstens Cc: Hendrik Brueckner LKML-Reference: <20090825160237.GG4639@cetus.boeblingen.de.ibm.com> Signed-off-by: Frederic Weisbecker --- kernel/tracepoint.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index 1a6a453b7efb..9489a0a9b1be 100644 --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -597,7 +597,9 @@ 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_TRACEPOINT); + /* Skip kernel threads. */ + if (t->mm) + set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT); } while_each_thread(g, t); read_unlock_irqrestore(&tasklist_lock, flags); }