Oleg Nesterov <o...@redhat.com> writes:
> On 07/10, Eric W. Biederman wrote:
>>
>> Now that we can make the distinction use PIDTYPE_TGID rather than
>> PIDTYPE_PID.
>
> Wai, wait, this doesn't look right...
>
>> There is no immediate effect as they point point at the
>> same task,
>
> How so? pid_task(pid, PIDTYPE_TGID) will return NULL unless this pid is
> actually
> a group leader's pid,
>
>> --- a/kernel/signal.c
>> +++ b/kernel/signal.c
>> @@ -1315,7 +1315,7 @@ int kill_pid_info(int sig, struct siginfo *info,
>> struct pid *pid)
>>
>> for (;;) {
>> rcu_read_lock();
>> - p = pid_task(pid, PIDTYPE_PID);
>> + p = pid_task(pid, PIDTYPE_TGID);
>> if (p)
>> error = group_send_sig_info(sig, info, p);
>
> So, currently kill(pid_nr) always works, even if pid_nr is a sub-thread's tid.
>
> After this change kill(2) will always fail with -ESRCH in this case.
>
> Or I am totally confused?
No you are not.
That does at least need to be documented in the description of the
patch.
In practice since glibc does not make thread id's available I don't
expect anyone relies on this behavior. Since no one relies on it we
can change it without creating a regression.
I believe this can be described as fixing a bug that we were not able to
before the introduction of PIDTYPE_TGID.
I will update my change description.
Eric
