Messages in this thread | | | From | Grant Likely <> | Subject | Re: [PATCH] driver core: add wait event for deferred probe | Date | Wed, 13 Feb 2013 21:36:23 +0000 |
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On Tue, 12 Feb 2013 10:52:10 +0800, Haojian Zhuang <haojian.zhuang@linaro.org> wrote: > On 12 February 2013 07:10, Andrew Morton <akpm@linux-foundation.org> wrote: > > On Sun, 10 Feb 2013 00:57:57 +0800 > > Haojian Zhuang <haojian.zhuang@linaro.org> wrote: > > > >> do_initcalls() could call all driver initialization code in kernel_init > >> thread. It means that probe() function will be also called from that > >> time. After this, kernel could access console & release __init section > >> in the same thread. > >> > >> But if device probe fails and moves into deferred probe list, a new > >> thread is created to reinvoke probe. If the device is serial console, > >> kernel has to open console failure & release __init section before > >> reinvoking failure. Because there's no synchronization mechanism. > >> Now add wait event to synchronize after do_initcalls(). > > > > It sounds like this: > > > > static int __ref kernel_init(void *unused) > > { > > kernel_init_freeable(); > > /* need to finish all async __init code before freeing the memory */ > > async_synchronize_full(); > > > > is designed to prevent the problem you describe? > > > It can't prevent the problem that I described. Because deferred_probe() > is introduced recently. > > All synchronization should be finished just after do_initcalls(). Since > load_default_modules() is also called in the end of kernel_init_freeable(), > I'm not sure that whether I could remove async_synchronize_full() > here. So I didn't touch it. > > >> --- a/init/main.c > >> +++ b/init/main.c > >> @@ -786,6 +786,7 @@ static void __init do_basic_setup(void) > >> do_ctors(); > >> usermodehelper_enable(); > >> do_initcalls(); > >> + wait_for_device_probe(); > >> } > > > > Needs a nice comment here explaining what's going on. > > No problem. I'll add comment here.
Actually, this approach will create new problems. There is no guarantee that a given device will be able to initialize before exiting do_basic_setup(). If, for instance, a device depends on a resource provided by a module, then it will just keep deferring. In that case you've got a hung kernel.
I think what you really want is the following:
static int deferred_probe_initcall(void) { deferred_wq = create_singlethread_workqueue("deferwq"); if (WARN_ON(!deferred_wq)) return -ENOMEM;
driver_deferred_probe_enable = true; + deferred_probe_work_func(NULL); - driver_deferred_probe_trigger(); return 0; } late_initcall(deferred_probe_initcall);
Or something similar. That would guarantee that as many passes as are needed (which in practical terms only means a couple) for device probing to settle down before exiting the initcall processing. That should achieve the effect you desire.
It still masks the __init section issue by making it a lot less likely, but it does ensure that all of the built-in driver dependency order issues are processed before continuing on to userspace.
g.
-- Grant Likely, B.Sc, P.Eng. Secret Lab Technologies, Ltd.
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