Add an API to set/clear the kernel wide tracing thread flags. Implemented in kernel/sched.c. Updates thread flags *asynchronously* while holding the tasklist lock. Upon fork, the flag must be re-copied while the tasklist lock is held. Signed-off-by: Mathieu Desnoyers --- include/linux/sched.h | 3 ++ kernel/fork.c | 9 ++++++++ kernel/sched.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 67 insertions(+) Index: linux-2.6-lttng/include/linux/sched.h =================================================================== --- linux-2.6-lttng.orig/include/linux/sched.h 2007-12-05 20:50:29.000000000 -0500 +++ linux-2.6-lttng/include/linux/sched.h 2007-12-05 20:54:32.000000000 -0500 @@ -2000,6 +2000,9 @@ static inline void migration_init(void) } #endif +extern void clear_kernel_trace_flag_all_tasks(void); +extern void set_kernel_trace_flag_all_tasks(void); + #endif /* __KERNEL__ */ #endif Index: linux-2.6-lttng/kernel/fork.c =================================================================== --- linux-2.6-lttng.orig/kernel/fork.c 2007-12-05 20:54:00.000000000 -0500 +++ linux-2.6-lttng/kernel/fork.c 2007-12-05 20:54:32.000000000 -0500 @@ -1241,6 +1241,15 @@ static struct task_struct *copy_process( !cpu_online(task_cpu(p)))) set_task_cpu(p, smp_processor_id()); + /* + * The state of the parent's TIF_KTRACE flag may have changed + * since it was copied in dup_task_struct() so we re-copy it here. + */ + if (test_thread_flag(TIF_KERNEL_TRACE)) + set_tsk_thread_flag(p, TIF_KERNEL_TRACE); + else + clear_tsk_thread_flag(p, TIF_KERNEL_TRACE); + /* CLONE_PARENT re-uses the old parent */ if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) p->real_parent = current->real_parent; Index: linux-2.6-lttng/kernel/sched.c =================================================================== --- linux-2.6-lttng.orig/kernel/sched.c 2007-12-05 20:54:00.000000000 -0500 +++ linux-2.6-lttng/kernel/sched.c 2007-12-05 20:54:32.000000000 -0500 @@ -7394,3 +7394,58 @@ struct cgroup_subsys cpuacct_subsys = { .subsys_id = cpuacct_subsys_id, }; #endif /* CONFIG_CGROUP_CPUACCT */ + +static DEFINE_MUTEX(kernel_trace_mutex); +static int kernel_trace_refcount; + +/** + * clear_kernel_trace_flag_all_tasks - clears all TIF_KERNEL_TRACE thread flags. + * + * This function iterates on all threads in the system to clear their + * TIF_KERNEL_TRACE flag. Setting the TIF_KERNEL_TRACE flag with the + * tasklist_lock held in copy_process() makes sure that once we finish clearing + * the thread flags, all threads have their flags cleared. + */ +void clear_kernel_trace_flag_all_tasks(void) +{ + struct task_struct *p; + struct task_struct *t; + + mutex_lock(&kernel_trace_mutex); + if (--kernel_trace_refcount) + goto end; + read_lock(&tasklist_lock); + do_each_thread(p, t) { + clear_tsk_thread_flag(t, TIF_KERNEL_TRACE); + } while_each_thread(p, t); + read_unlock(&tasklist_lock); +end: + mutex_unlock(&kernel_trace_mutex); +} +EXPORT_SYMBOL_GPL(clear_kernel_trace_flag_all_tasks); + +/** + * set_kernel_trace_flag_all_tasks - sets all TIF_KERNEL_TRACE thread flags. + * + * This function iterates on all threads in the system to set their + * TIF_KERNEL_TRACE flag. Setting the TIF_KERNEL_TRACE flag with the + * tasklist_lock held in copy_process() makes sure that once we finish setting + * the thread flags, all threads have their flags set. + */ +void set_kernel_trace_flag_all_tasks(void) +{ + struct task_struct *p; + struct task_struct *t; + + mutex_lock(&kernel_trace_mutex); + if (kernel_trace_refcount++) + goto end; + read_lock(&tasklist_lock); + do_each_thread(p, t) { + set_tsk_thread_flag(t, TIF_KERNEL_TRACE); + } while_each_thread(p, t); + read_unlock(&tasklist_lock); +end: + mutex_unlock(&kernel_trace_mutex); +} +EXPORT_SYMBOL_GPL(set_kernel_trace_flag_all_tasks); -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/