From: Steven Rostedt Impact: fix There is a nasy race in startup of a new process running the function graph tracer. In fork.c: total_forks++; spin_unlock(¤t->sighand->siglock); write_unlock_irq(&tasklist_lock); ftrace_graph_init_task(p); proc_fork_connector(p); cgroup_post_fork(p); return p; The new task is free to run as soon as the tasklist_lock is released. This is before the ftrace_graph_init_task. If the task does run it will be using the same ret_stack and curr_ret_stack as the parent. This will cause horrible crashes that are nasty to debug. This patch moves the ftrace_graph_init_task to just after the alloc_pid code. This fixes the above race. Signed-off-by: Steven Rostedt --- kernel/fork.c | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index afb376d..91cca76 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1142,6 +1142,8 @@ static struct task_struct *copy_process(unsigned long clone_flags, } } + ftrace_graph_init_task(p); + p->pid = pid_nr(pid); p->tgid = p->pid; if (clone_flags & CLONE_THREAD) @@ -1150,7 +1152,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, if (current->nsproxy != p->nsproxy) { retval = ns_cgroup_clone(p, pid); if (retval) - goto bad_fork_free_pid; + goto bad_fork_free_graph; } p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL; @@ -1243,7 +1245,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, spin_unlock(¤t->sighand->siglock); write_unlock_irq(&tasklist_lock); retval = -ERESTARTNOINTR; - goto bad_fork_free_pid; + goto bad_fork_free_graph; } if (clone_flags & CLONE_THREAD) { @@ -1276,11 +1278,12 @@ static struct task_struct *copy_process(unsigned long clone_flags, total_forks++; spin_unlock(¤t->sighand->siglock); write_unlock_irq(&tasklist_lock); - ftrace_graph_init_task(p); proc_fork_connector(p); cgroup_post_fork(p); return p; +bad_fork_free_graph: + ftrace_graph_exit_task(p); bad_fork_free_pid: if (pid != &init_struct_pid) free_pid(pid); -- 1.5.6.5 -- -- 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/