Re: [PATCH 1/3] [PATCH i386] during VM oom condition, kill all threads in process group

[ebiederm@xmission.com (Eric W. Biederman)]

Will Schmidt <will_schmidt@vnet.ibm.com> writes:

> On Fri, 2007-06-08 at 12:32 -0700, Andrew Morton wrote:
>> On Fri, 08 Jun 2007 14:19:18 -0500
>> Will Schmidt <will_schmidt@vnet.ibm.com> wrote:
>> 
>> > > > > zap_other_threads() requires tasklist_lock.
>> > 
>
>> In fact, it's probably the case that rcu_read_lock() is now sufficient
>> locking coverage for zap_other_threads() (cc's people).
>> 
>> It had better be, because do_group_exit() forgot to take tasklist_lock.  It
>> is perhaps relying upon spin_lock()'s hidden rcu_read_lock() properties
>> without so much as a code comment, which would be somewhat nasty of it.
>
>> You could perhaps just call do_group_exit() from within the fault
>> handler,
>> btw.
>
> Yup, so looks like I can actually replace the existing do_exit() call
> with do_group_exit().   I'll sit on this for a bit to give other folks a
> chance to comment on which lock call is sufficient, read_lock() or
> rcu_read_lock(), etc;  and do_group_exit()'s issue with taking
> tasklist_lock. 

No.  The rcu_read_lock is not sufficient.
Yes.  sighand->siglock is enough, and we explicitly take it in
do_group_exit before calling zap_other_threads.

Unless I have completely miss-understood this thread.

Eric