On Fri, 13 Apr 2007 15:51:29 -0600 [EMAIL PROTECTED] (Eric W. Biederman) wrote:
> Andrew Morton <[EMAIL PROTECTED]> writes: > > > On Fri, 13 Apr 2007 17:02:01 +0400 > > Oleg Nesterov <[EMAIL PROTECTED]> wrote: > > > >> If kernel_thread(kthread) succeeds, kthread() can not fail on its path to > >> complete(&create->started) + schedule(). After that it can't be woken > >> because > >> nobody can see the new task yet. This means: > >> > >> - we don't need tasklist_lock for find_task_by_pid(). > >> > >> - create_kthread() doesn't need to wait for create->started. Instead, > >> kthread_create() first waits for create->created to get the result of > >> kernel_thread(), then waits for create->started to synchronize with > >> kthread(). > > > > Why don't we need tasklist_lock for find_task_by_pid()? I'd have though > > that > > we'd at least need rcu_read_lock(), and I'm not sure that the implicit > > understanding of pid-management internals here is a great idea. > > We need rcu_read_lock(). Or else something could permute the pid hash table > and get us into trouble. > OK, I fixed that up. The next patch (make-kthread_stop-scalable) removes the find_task_by_pid() anyway. Our kthread creation performance will be pretty poor anyway, due to the need to do two (or more?) context switches. If we ever need super-low-latency kernel thread creation (eg, on-demand threads for AIO) then that code would need to go direct to kernel_thread(), I guess. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
