2010/6/28 Peter Zijlstra <peterz@xxxxxxxxxxxxx>:
> So if ->rb_leftmost is NULL, then the if (!left) check in
> __pick_next_entity() would return null.
>
> As to the NULL deref in in pick_next_task_fair()->set_next_entity() that
> should never happen because pick_next_task_fair() will bail
> on !->nr_running.
>
> Furthermore, you've failed to mention what kernel version you're looking
> at.
>
The kernel version is 2.6.35-rc3, and 2.6.34 has the same code.
For nr->running, if current is the only process in the run queue, then
nr->running would not be zero.
1784 if (!cfs_rq->nr_running)
1785 return NULL;
pick_next_task_fair() could pass above check and run to following:
1787 do {
1788 se = pick_next_entity(cfs_rq);
1789 set_next_entity(cfs_rq, se);
1790 cfs_rq = group_cfs_rq(se);
1791 } while (cfs_rq);
Then pick_next_entity will get NULL for current is the root rb_node.
Then set_next_entity would fail on NULL deference.
--
Thanks and Best Regards,
shenghui
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