Messages in this thread | | | Subject | Re: [PATCH rc5-mm] pids: kill PIDTYPE_TGID | From | (Eric W. Biederman) | Date | Wed, 08 Mar 2006 15:12:59 -0700 |
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Oleg Nesterov <oleg@tv-sign.ru> writes:
> Eric W. Biederman wrote: >> >> > p->group_leader = current->group_leader; >> > + list_add_tail_rcu(&p->thread_group, ¤t->thread_group); >> Can this be: >> list_add_tail_rcu(&p->thread_group, ¤t->group_leader->thread_group); > > Done. > >> That way at least the odds of missing a new task_struct when doing an >> rcu traversal are reduced almost to 0. > > Am I understand correctly? This change has effect when we are doing the > traversal starting from ->group_leader in a "best effort" manner lockless, > yes?
Yes. The important point for reasoning about it is that we have a fixed point that we append or prepend to.
I think I have finally figured out the invariants we will need to send signals using just the rcu_read_lock(). In that case we want to traverse the list in such a way that we are guaranteed to never see new entries. That gives us an atomic snapshot of the tasks to send signals to, and it gives us a progress guarantee.
Now I need to look and see if any one has documented any rules regarding atomicity of sending signals to a group of processes.
> [PATCH rc5-mm] pids: kill PIDTYPE_TGID > > depends on pidhash-dont-count-idle-threads.patch > > This patch kills PIDTYPE_TGID pid_type thus saving one hash table > in kernel/pid.c and speeding up subthreads create/destroy a bit. > It is also a preparation for the further tref/pids rework. > > This patch adds 'struct list_head thread_group' to 'struct task_struct' > instead. > > We don't detach group leader from PIDTYPE_PID namespace until another > thread inherits it's ->pid == ->tgid, so we are safe wrt premature > free_pidmap(->tgid) call. > > Currently there are no users of find_task_by_pid_type(PIDTYPE_TGID). > Should the need arise, we can use find_task_by_pid()->group_leader. > > include/linux/pid.h | 1 - > include/linux/sched.h | 11 ++++++++--- > kernel/exit.c | 10 +--------- > kernel/fork.c | 4 +++- > 4 files changed, 12 insertions(+), 14 deletions(-) > > Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-By: Eric Biederman <ebiederm@xmission.com> - 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/
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