On 07/21, Yafang Shao wrote: > > On Thu, Jul 20, 2023 at 7:36 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > Adding support to specify pid for uprobe_multi link and the uprobes > > are created only for task with given pid value. > > Is it possible to use tgid as the filter? > It would be helpful when we uprobe a library file but want to filter > out a multi-threaded task only. I leave this to you and Jiri, just some notes... I think it is possible but needs some complications. uprobe_prog_run() needs a trivial change, - if (link->task && current != link->task) + if (link->task && same_thread_group(current, link->task) ->signal is tied to task_struct so this should work even if link->task has already exited. bpf_uprobe_multi_link_attach() should probably use get_pid_task(find_vpid(pid), PIDTYPE_TGID); to ensure that 'pid' is actually tgid. But. uprobe_multi_link_filter() can return F if the group leader has already exited, in this case uprobe->link->task->mm == NULL. Perhaps we can simply ignore this case, a zombie group-leader is not that common. Or we can add uprobe->link->mm = get_task_mm(uprobe->link->task->mm) for uprobe_multi_link_filter(). Or. We can simply kill uprobe_multi_link_filter(). In this case uprobe_register() can touch CLONE_VM'ed mm's we are not interested in, but everything should work correctly. Oleg.
