Re: [PATCH v2] driver core: add wait event for deferred probe

From: Grant Likely
Date: Wed Feb 13 2013 - 16:40:09 EST

On Tue, 12 Feb 2013 10:58:35 +0800, Haojian Zhuang <haojian.zhuang@xxxxxxxxxx> 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().
> Changelog:
> v2: add comments on wait_for_device_probe().
> Signed-off-by: Haojian Zhuang <haojian.zhuang@xxxxxxxxxx>

As replied to on v1 of your patch, this change will cause a deadlock.
The following change would do the same without the deadlock issue:

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;

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