Messages in this thread | | | Date | Fri, 12 Mar 2021 17:41:20 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH v4] do_wait: make PIDTYPE_PID case O(1) instead of O(n) |
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On 03/11, Jim Newsome wrote: > > +static bool is_effectively_child(struct wait_opts *wo, bool ptrace, > + struct task_struct *target) > +{ > + struct task_struct *parent = > + !ptrace ? target->real_parent : target->parent; > + > + return current == parent || (!(wo->wo_flags & __WNOTHREAD) && > + same_thread_group(current, parent)); > +} > + > +/* > + * Optimization for waiting on PIDTYPE_PID. No need to iterate through child > + * and tracee lists to find the target task. > + */ > +static int do_wait_pid(struct wait_opts *wo) > +{ > + bool ptrace; > + struct task_struct *target; > + int retval; > + > + ptrace = false; > + > + /* A non-ptrace wait can only be performed on a thread group leader. */ > + target = pid_task(wo->wo_pid, PIDTYPE_TGID); > + > + if (target && is_effectively_child(wo, ptrace, target)) { > + retval = wait_consider_task(wo, ptrace, target); > + if (retval) > + return retval; > + } > + > + ptrace = true; > + > + /* A ptrace wait can be done on non-thread-group-leaders. */ > + if (!target) > + target = pid_task(wo->wo_pid, PIDTYPE_PID); > + > + if (target && is_effectively_child(wo, ptrace, target)) { > + retval = wait_consider_task(wo, ptrace, target);
No, this is not right... You need to check target->ptrace != 0.
I know that Eric suggests to not use thread_group_leader() and I won't argue even if I don't really agree.
Up to you, but to me something like
do_wait_pid() { target = pid_task(wo->wo_pid, PIDTYPE_PID);
if (!target) return 0;
if (thread_group_leader(target) && is_effectively_child(wo, 0, target) { ... }
if (target->ptrace && is_effectively_child(wo, 1, target) { ... }
return 0;
}
looks more simple/clean.
Oleg.
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