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SubjectRe: [PATCH v2] driver core: add wait event for deferred probe
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On Tue, 2013-02-12 at 10:58 +0800, Haojian Zhuang 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().
Can you describe the problem you are facing in detail i.e. without this
patch what is happening weird?
>
> Changelog:
> v2: add comments on wait_for_device_probe().
>
> Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.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 int __ref kernel_init(void *unused)
{
kernel_init_freeable();
/* need to finish all async __init code before freeing the
memory */
async_synchronize_full();

Is not your wait_for_device_probe() also calling
async_synchronize_full() function?AFAIK this function will send all the
instructions before moving ahead no?My understanding originates from the
below text.

From kernel/async.c file
Subsystem/driver initialization code that scheduled asynchronous probe
functions, but which shares global resources with other
drivers/subsystems that do not use the asynchronous call feature, need
to do a full synchronization with the async_synchronize_full() function,
before returning from their init function. This is to maintain strict
ordering between the asynchronous and synchronous parts of the kernel.

> }
>
> static void __init do_pre_smp_initcalls(void)




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