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

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Date:	Tue, 12 Feb 2013 10:58:35 +0800
From:	Haojian Zhuang <haojian.zhuang@...aro.org>
To:	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, grant.likely@...retlab.ca, arnd@...db.de,
	broonie@...nsource.wolfsonmicro.com, akpm@...ux-foundation.org
Cc:	patches@...aro.org, Haojian Zhuang <haojian.zhuang@...aro.org>
Subject: [PATCH v2] driver core: add wait event for deferred probe

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>
---
 drivers/base/dd.c |    8 +++++---
 init/main.c       |    2 ++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 65631015..23db672 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -53,6 +53,9 @@ static LIST_HEAD(deferred_probe_pending_list);
 static LIST_HEAD(deferred_probe_active_list);
 static struct workqueue_struct *deferred_wq;
 
+static atomic_t probe_count = ATOMIC_INIT(0);
+static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
+
 /**
  * deferred_probe_work_func() - Retry probing devices in the active list.
  */
@@ -77,6 +80,7 @@ static void deferred_probe_work_func(struct work_struct *work)
 		private = list_first_entry(&deferred_probe_active_list,
 					typeof(*dev->p), deferred_probe);
 		dev = private->device;
+		atomic_dec(&probe_count);
 		list_del_init(&private->deferred_probe);
 
 		get_device(dev);
@@ -257,9 +261,6 @@ int device_bind_driver(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(device_bind_driver);
 
-static atomic_t probe_count = ATOMIC_INIT(0);
-static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
-
 static int really_probe(struct device *dev, struct device_driver *drv)
 {
 	int ret = 0;
@@ -308,6 +309,7 @@ probe_failed:
 		/* Driver requested deferred probing */
 		dev_info(dev, "Driver %s requests probe deferral\n", drv->name);
 		driver_deferred_probe_add(dev);
+		atomic_inc(&probe_count);
 	} else if (ret != -ENODEV && ret != -ENXIO) {
 		/* driver matched but the probe failed */
 		printk(KERN_WARNING
diff --git a/init/main.c b/init/main.c
index 63534a1..141a6a4 100644
--- a/init/main.c
+++ b/init/main.c
@@ -786,6 +786,8 @@ static void __init do_basic_setup(void)
 	do_ctors();
 	usermodehelper_enable();
 	do_initcalls();
+	/* wait all deferred probe finished & prepare to drop __init section */
+	wait_for_device_probe();
 }
 
 static void __init do_pre_smp_initcalls(void)
-- 
1.7.10.4

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