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Date: Mon, 5 May 2014 10:28:05 +0800
From: Wei Yang <weiyang@...ux.vnet.ibm.com>
To: Wei Yang <weiyang@...ux.vnet.ibm.com>
Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
xiaoguangrong@...ux.vnet.ibm.com
Subject: Re: [PATCH] drivercore: fix a corner case for deferred probe
Hi, all
Anyone has some comment on this?
On Mon, Apr 21, 2014 at 09:53:22AM +0800, Wei Yang wrote:
>There is one corner case in deferred probe which will lead a device in
>"dream" in the deferred_probe_pending_list.
>
>Suppose we have three devices, Tom, Jerry and Spike. Tom and Jerry have a
>close relationship, Tom could be up until Jerry is up. Spike is an
>independent device.
>
>Device probe sequence: Tom -> Spike -> Jerry
>
>1. Tom probes, fails for deferred probe
> adds itself to pending list
>2. Spike probes, succeed
> move devices in pending list to active list
> trigger deferred probe
>3. Tom is taken off from active list
> probes and still fails, scheduled out
> not added to pending list this time
> (Tom is not in pending list neither in active list)
>4. Jerry probes, succeed
> move devices in pending list to active list(but Tom is not there)
> trigger deferred probe
> go through the active list
>5. Tom add itself to pending list
> and wait
>
>Tom will be trapped in the pending list until someone else help it out.
>
>This patch adds a counter of success probe. Every time a driver probe succeeds,
>this is increased by 1. In the deferred_probe_work_func, when probe fails and
>returns EPROBE_DEFER, it checks this counter. If some driver succeed to probe
>during this period, it adds itself to active list again.
>
>Signed-off-by: Wei Yang <weiyang@...ux.vnet.ibm.com>
>---
> drivers/base/base.h | 2 +-
> drivers/base/bus.c | 3 ++-
> drivers/base/dd.c | 14 +++++++++++++-
> 3 files changed, 16 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/base/base.h b/drivers/base/base.h
>index 24f4242..6315207 100644
>--- a/drivers/base/base.h
>+++ b/drivers/base/base.h
>@@ -105,7 +105,7 @@ extern void container_dev_init(void);
> struct kobject *virtual_device_parent(struct device *dev);
>
> extern int bus_add_device(struct device *dev);
>-extern void bus_probe_device(struct device *dev);
>+extern int bus_probe_device(struct device *dev);
> extern void bus_remove_device(struct device *dev);
>
> extern int bus_add_driver(struct device_driver *drv);
>diff --git a/drivers/base/bus.c b/drivers/base/bus.c
>index 59dc808..a050946 100644
>--- a/drivers/base/bus.c
>+++ b/drivers/base/bus.c
>@@ -543,7 +543,7 @@ out_put:
> *
> * - Automatically probe for a driver if the bus allows it.
> */
>-void bus_probe_device(struct device *dev)
>+int bus_probe_device(struct device *dev)
> {
> struct bus_type *bus = dev->bus;
> struct subsys_interface *sif;
>@@ -562,6 +562,7 @@ void bus_probe_device(struct device *dev)
> if (sif->add_dev)
> sif->add_dev(dev, sif);
> mutex_unlock(&bus->p->mutex);
>+ return ret;
> }
>
> /**
>diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>index 0605176..a10526d 100644
>--- a/drivers/base/dd.c
>+++ b/drivers/base/dd.c
>@@ -52,6 +52,7 @@ static DEFINE_MUTEX(deferred_probe_mutex);
> static LIST_HEAD(deferred_probe_pending_list);
> static LIST_HEAD(deferred_probe_active_list);
> static struct workqueue_struct *deferred_wq;
>+static u32 success_probe;
>
> /**
> * deferred_probe_work_func() - Retry probing devices in the active list.
>@@ -60,6 +61,8 @@ static void deferred_probe_work_func(struct work_struct *work)
> {
> struct device *dev;
> struct device_private *private;
>+ u32 old_success;
>+ int ret = 0;
> /*
> * This block processes every device in the deferred 'active' list.
> * Each device is removed from the active list and passed to
>@@ -80,6 +83,7 @@ static void deferred_probe_work_func(struct work_struct *work)
> list_del_init(&private->deferred_probe);
>
> get_device(dev);
>+ old_success = ACCESS_ONCE(success_probe);
>
> /*
> * Drop the mutex while probing each device; the probe path may
>@@ -98,7 +102,14 @@ static void deferred_probe_work_func(struct work_struct *work)
> device_pm_unlock();
>
> dev_dbg(dev, "Retrying from deferred list\n");
>- bus_probe_device(dev);
>+ ret = bus_probe_device(dev);
>+ if (ret == -EPROBE_DEFER) {
>+ mutex_lock(&deferred_probe_mutex);
>+ if (old_success != success_probe)
>+ list_move(&private->deferred_probe,
>+ &deferred_probe_active_list);
>+ mutex_unlock(&deferred_probe_mutex);
>+ }
>
> mutex_lock(&deferred_probe_mutex);
>
>@@ -147,6 +158,7 @@ static void driver_deferred_probe_trigger(void)
> * into the active list so they can be retried by the workqueue
> */
> mutex_lock(&deferred_probe_mutex);
>+ success_probe++;
> list_splice_tail_init(&deferred_probe_pending_list,
> &deferred_probe_active_list);
> mutex_unlock(&deferred_probe_mutex);
>--
>1.7.9.5
--
Richard Yang
Help you, Help me
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