Not sure I read this patch correctly, but at first glance it looks suspicious..
On 07/11, Peter Zijlstra wrote: > > +static void return_instance_timer(struct timer_list *timer) > +{ > + struct uprobe_task *utask = container_of(timer, struct uprobe_task, > ri_timer); > + task_work_add(utask->task, &utask->ri_task_work, TWA_SIGNAL); > +} What if utask->task sleeps in TASK_STOPPED/TASK_TRACED state before return from the ret-probed function? In this case it won't react to TWA_SIGNAL until debugger or SIGCONT wakes it up. --------------------------------------------------------------------------- And it seems that even task_work_add() itself is not safe... Suppose we have 2 ret-probed functions void f2() { ... } void f1() { ...; f2(); } A task T calls f1(), hits the bp, and calls prepare_uretprobe() which does mod_timer(&utask->ri_timer, jiffies + HZ); Then later it calls f2() and the pending timer expires after it enters the kernel, but before the next prepare_uretprobe() -> mod_timer(). In this case ri_task_work is already queued and the timer is pending again. Now. Even if T goes to the exit_to_user_mode_loop() path immediately, in theory nothing can guarantee that it will call get_signal/task_work_run in less than 1 second, it can be preempted. But T can sleep in xol_take_insn_slot() before return from handle_swbp(), and this is not so theoretical. Oleg.