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Date:	Mon, 28 Jul 2014 16:51:07 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Kay Sievers <kay@...y.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tim Gardner <tim.gardner@...onical.com>,
	Pierre Fersing <pierre-fersing@...rref.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Benjamin Poirier <bpoirier@...e.de>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	Santosh Rastapur <santosh@...lsio.com>,
	MPT-FusionLinux.pdl@...gotech.com, linux-scsi@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 1/3] driver core: enable drivers to use deferred probe from init

At Mon, 28 Jul 2014 07:34:25 -0700,
Luis R. Rodriguez wrote:
> 
> From: "Luis R. Rodriguez" <mcgrof@...e.com>
> 
> Tetsuo bisected and found that commit 786235ee "kthread: make
> kthread_create() killable" modified kthread_create() to bail as
> soon as SIGKILL is received. This is causing some issues with
> some drivers and at times boot. Joseph then found that failures
> occur as the systemd-udevd process sends SIGKILL to modprobe if
> probe on a driver takes over 30 seconds. When this happens probe
> will fail on any driver, its why booting on some system will fail
> if the driver happens to be a storage related driver. Some folks
> have suggested fixing this by modifying kthread_create() to not
> leave upon SIGKILL [3], upon review Oleg rejected this change and
> the discussion was punted out to systemd to see if the default
> timeout could be increased from 30 seconds to 120. The opinion of
> the systemd maintainers is that the driver's behavior should
> be fixed [4]. Linus seems to agree [5], however more recently even
> networking drivers have been reported to fail on probe since just
> writing the firmware to a device and kicking it can take easy over
> 60 seconds [6]. Benjamim was able to trace the issues recently
> reported on cxgb4 down to the same systemd-udevd 30 second timeout [6].
> 
> This is an alternative solution which enables drivers that are
> known to take long to use deferred probe workqueue. This avoids
> the 30 second timeout and lets us annotate drivers with long
> init sequences.
> 
> As drivers determine a component is not yet available and needs
> to defer probe you'll be notified this happen upon init for each
> device but now with a message such as:
> 
> pci 0000:03:00.0: Driver cxgb4 requests probe deferral on init
> 
> You should see one of these per struct device probed.
> 
> [0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1276705
> [1] https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1297248
> [2] http://lists.freedesktop.org/archives/systemd-devel/2014-March/018006.html
> [3] http://thread.gmane.org/gmane.linux.ubuntu.devel.kernel.general/39123
> [4] http://article.gmane.org/gmane.comp.sysutils.systemd.devel/17860
> [5] http://article.gmane.org/gmane.linux.kernel/1671333
> [6] https://bugzilla.novell.com/show_bug.cgi?id=877622
> 
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Joseph Salisbury <joseph.salisbury@...onical.com>
> Cc: Kay Sievers <kay@...y.org>
> Cc: One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
> Cc: Tim Gardner <tim.gardner@...onical.com>
> Cc: Pierre Fersing <pierre-fersing@...rref.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Benjamin Poirier <bpoirier@...e.de>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>
> Cc: Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>
> Cc: Sreekanth Reddy <sreekanth.reddy@...gotech.com>
> Cc: Abhijit Mahajan <abhijit.mahajan@...gotech.com>
> Cc: Hariprasad S <hariprasad@...lsio.com>
> Cc: Santosh Rastapur <santosh@...lsio.com>
> Cc: MPT-FusionLinux.pdl@...gotech.com
> Cc: linux-scsi@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Signed-off-by: Luis R. Rodriguez <mcgrof@...e.com>
> ---
>  drivers/base/dd.c      | 15 ++++++++++++++-
>  include/linux/device.h | 12 ++++++++++++
>  2 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index e4ffbcf..7a271dc 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -374,6 +374,19 @@ void wait_for_device_probe(void)
>  }
>  EXPORT_SYMBOL_GPL(wait_for_device_probe);
>  
> +static int __driver_probe_device(struct device_driver *drv, struct device *dev)
> +{
> +	if (drv->delay_probe && !dev->init_delayed_probe) {
> +		dev_info(dev, "Driver %s requests probe deferral on init\n",
> +			 drv->name);
> +		dev->init_delayed_probe = true;
> +		driver_deferred_probe_add(dev);
> +		return -EPROBE_DEFER;
> +	}
> +
> +	return really_probe(dev, drv);
> +}
> +
>  /**
>   * driver_probe_device - attempt to bind device & driver together
>   * @drv: driver to bind a device to
> @@ -396,7 +409,7 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
>  		 drv->bus->name, __func__, dev_name(dev), drv->name);
>  
>  	pm_runtime_barrier(dev);
> -	ret = really_probe(dev, drv);
> +	ret = __driver_probe_device(drv, dev);
>  	pm_request_idle(dev);
>  
>  	return ret;
> diff --git a/include/linux/device.h b/include/linux/device.h
> index af424ac..11da1b7 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -200,6 +200,12 @@ extern struct klist *bus_get_device_klist(struct bus_type *bus);
>   * @owner:	The module owner.
>   * @mod_name:	Used for built-in modules.
>   * @suppress_bind_attrs: Disables bind/unbind via sysfs.
> + * @delay_probe: this driver is requesting a deferred probe since
> + *	initialization. This can be desirable if its known the device probe
> + *	or initialization takes more than 30 seconds.
> + * @delayed_probe_devs: devices which have gone through a delayed probe. This
> + * 	is used internally by the driver core to keep track of which devices
> + * 	have gone through a delayed probe.
>   * @of_match_table: The open firmware table.
>   * @acpi_match_table: The ACPI match table.
>   * @probe:	Called to query the existence of a specific device,
> @@ -234,6 +240,9 @@ struct device_driver {
>  
>  	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
>  
> +	bool delay_probe;		/* requests deferred probe */
> +	struct list_head delayed_probe_devs;
> +

This field isn't used anywhere actually in the patch...?


Takashi

>  	const struct of_device_id	*of_match_table;
>  	const struct acpi_device_id	*acpi_match_table;
>  
> @@ -715,6 +724,8 @@ struct acpi_dev_node {
>   *
>   * @offline_disabled: If set, the device is permanently online.
>   * @offline:	Set after successful invocation of bus type's .offline().
> + * @init_delayed_probe: lets the coore keep track if the device has already
> + * 	gone through a delayed probe upon init.
>   *
>   * At the lowest level, every device in a Linux system is represented by an
>   * instance of struct device. The device structure contains the information
> @@ -793,6 +804,7 @@ struct device {
>  
>  	bool			offline_disabled:1;
>  	bool			offline:1;
> +	bool			init_delayed_probe:1;
>  };
>  
>  static inline struct device *kobj_to_dev(struct kobject *kobj)
> -- 
> 2.0.1
> 
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