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List:       ssic-linux-users
Subject:    [SSI-users] Thread group migration
From:       Vladimir Razgulin <onegulin () gmail ! com>
Date:       2006-01-18 17:51:01
Message-ID: bf0eedee0601180951m5dad5305lde3a06fb6b74953c () mail ! gmail ! com
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All,

Please, correct me if I'm wrong,
but it looks like the thread group migration didn't ever work for 1.9.1 openssi
on 2.6-based Linux kernel.
The changes in 2.6 broke the logic of add_thread_group() function
(cluster/ssi/vproc/dvp_move.c). I'd like to mention just few from
several issues
I've found trying to make it working:

1. The task list with init_task as a head doesn't include all the
tasks anymore, but only thread leaders. That means for_each_process(t)
loop as it's used in add_thread_group() function can't find all the
tasks to be migrated,
when add_thread_group() is called from setup_pid_move().
That results in EINVAL return code with "cannot find all shares"
kernel debug message.

2. task_struct has a pointer to group_info structure, and the instance
of this group_info data is shared between processes when they are
created by fork().
The group_info information is copied only on the first write (copy-on-write).
That means group_info is normally shared between all the processes in a tree
started from a shell interpreter process, unless it's explicitly
written back with
setgroups().
That results in EINVAL return code on a migration request,
and "partially shared with  process" kernel debug message
for a process and its parent (bash).

3. p->sysvsem.undo_list almost always is NULL for all the processes,
so add_thread_group() thinks that they all are partially shared with each other.

So, my questions are:
Should it be mentioned explicitly that thread group migration doesn't
work in 1.9.1 and, I believe, in 1.9.2pre?
Are there any plans to make in working in 2.x?

Thanks
Vladimir


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