On Mon, Apr 30, 2007 at 10:09:38AM -0700, Paul Menage wrote:
> Paul, is there any reason why we need to do a write_lock() on
> tasklist_lock if we're just trying to block fork, or is it just
> historical accident? Wouldn't it be fine to do a read_lock()?
Good point ..read_lock() will probably suffice in update_nodemask which
means we don't need the patch I sent earlier.
Paul (Jackson),
This made me see another race in update_nodemask vs fork:
Lets say cpuset CS1 has only one task T1 to begin with.
update_nodemask(CS1) T1 in do_fork()
CPU0 CPU1
=============================================================
cpuset_fork();
mpol_copy();
ntasks = atomic_read(&cs->count);
[ntasks = 2, accounting new born child T2]
cs->mems_allowed = something;
set_cpuset_being_rebound()
write/read_lock(tasklist_lock);
do_each_thread {
/* Finds only T1 */
mmarray[] = ..
} while_each_thread();
write/read_unlock(tasklist_lock);
write_lock(tasklist_lock);
/* Add T2, child of T1 to tasklist */
write_unlock(tasklist_lock);
for (i = 0; i < n; i++) {
mpol_rebind_mm(..);
}
In this for loop, we migrate only T1's ->mm. T2's->mm isn't migrated
AFAICS.
Is that fine?
--
Regards,
vatsa
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