Re: [rfc][patch] Avoid taking global tasklist_lock for single threaded process at getrusage()

[Ravikiran G Thirumalai <kiran@scalex86.org>]

On Wed, Dec 21, 2005 at 01:22:24PM -0800, Christoph Lameter wrote:
> On Wed, 21 Dec 2005, Ravikiran G Thirumalai wrote:
> 
> > We did look at that. Cases RUSAGE_CHILDREN and RUSAGE_SELF are always called by the 
> > current task, so we can avoid tasklist locking there.
> > getrusage for non-current tasks are always called with RUSAGE_BOTH.
> > We ensure we  always take the siglock for RUSAGE_BOTH case, so that the
> > p->signal* fields are protected and take the tasklist_lock only if we have 
> > to traverse the tasklist hashlist. Isn't this safe?
> 
> Sounds okay. But its complex in the way its is coded now and its easy to 
> assume that one can call getrusage with any parameter from inside the 
> kernel. Maybe we can have a couple of separate functions 
> 
> rusage_children()
> rusage_self()
> rusage_both()
> 
> ?
> 
> Only rusage_both would take a task_struct * parameter. The others would 
> only operate on current. Change all the locations that call getrusage with 
> RUSAGE_BOTH to call rusage_both().

Yes.  This would indeed be better. I will do that change.

Thanks,
Kiran