Messages in this thread | | | Date | Wed, 9 Apr 2014 20:30:17 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/5] sched: Convert thread_group_cputime() to use for_each_thread() |
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On Wed, Apr 09, 2014 at 07:32:34PM +0200, Oleg Nesterov wrote: > On 04/09, Peter Zijlstra wrote: > > > > On Wed, Apr 09, 2014 at 06:11:18PM +0200, Frederic Weisbecker wrote: > > > do_each_thread/while_each_thread iterators are deprecated by > > > for_each_thread/for_each_process_thread() APIs. > > > > > > Lets convert the callers in the cputime code accounting. The ultimate > > > goal is to remove the struct task_struct::thread_group field and > > > the corresponding do_each_thread/while_each_thread iterators that are > > > RCU unsafe. > > > > > > It also makes thread_group_cputime() eventually RCU-safe. > > > > this fails to explain how the current code is broken. > > while_each_thread(g, t) will loop forever if g exits and removes itself > from ->thread_group. This can happen even if it is the group leader, > de_thread() can do this. > > Another problem is that it is used wrongly very often, even if > while_each_thread() was fine people forget to check pid_alive() to ensure > it didn't exit even before we take rcu_read_lock(). > > for_each_thread(p, t) is always safe. Unless p's task_struct can't go away, > of course. > > But there is a difference. Ignoring the bug above > > p = g; > do { > printk("pid=%d\n", p->pid); > } while_each_thread(g, p); > > always prints at least one pid. > > for_each_thread(g, p) > printk("pid=%d\n", p->pid); > > can print nothing if g has already exited.
Cute,.. and all that lives in sched.h and I wasn't even Cc'ed :-(
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