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

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Date:	Wed, 13 Feb 2013 21:39:59 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Haojian Zhuang <haojian.zhuang@...aro.org>,
	gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
	rusty@...tcorp.com.au, hpa@...ux.intel.com, jim.cromie@...il.com,
	linux-kernel@...r.kernel.org, linux@....linux.org.uk,
	linus.walleij@...aro.org, arnd@...db.de,
	broonie@...nsource.wolfsonmicro.com, akpm@...ux-foundation.org
Cc:	patches@...aro.org, Haojian Zhuang <haojian.zhuang@...aro.org>
Subject: Re: [PATCH v2] driver core: add wait event for deferred probe

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

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;
 }
 late_initcall(deferred_probe_initcall);

g.
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