[BACKPORT 4.4.y] PM / sleep: prohibit devices probing during suspend/hibernation

From: Chunyan Zhang
Date: Wed Jun 05 2019 - 07:19:32 EST


From: "Strashko, Grygorii" <grygorii.strashko@xxxxxx>

[ Upstream commit 013c074f8642d8e815ad670601f8e27155a74b57 ]

It is unsafe [1] if probing of devices will happen during suspend or
hibernation and system behavior will be unpredictable in this case.
So, let's prohibit device's probing in dpm_prepare() and defer their
probing instead. The normal behavior will be restored in
dpm_complete().

This patch introduces new DD core APIs:
device_block_probing()
It will disable probing of devices and defer their probes instead.
device_unblock_probing()
It will restore normal behavior and trigger re-probing of deferred
devices.

[1] https://lkml.org/lkml/2015/9/11/554

Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
Acked-by: Pavel Machek <pavel@xxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Chunyan Zhang <zhang.chunyan@xxxxxxxxxx>
---
drivers/base/base.h | 2 ++
drivers/base/dd.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++-
drivers/base/power/main.c | 17 +++++++++++++++++
3 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index 1782f3a..e05db38 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -131,6 +131,8 @@ extern void device_remove_groups(struct device *dev,
extern char *make_class_name(const char *name, struct kobject *kobj);

extern int devres_release_all(struct device *dev);
+extern void device_block_probing(void);
+extern void device_unblock_probing(void);

/* /sys/devices directory */
extern struct kset *devices_kset;
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index d888741..ddee3456 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -55,6 +55,13 @@ static struct workqueue_struct *deferred_wq;
static atomic_t deferred_trigger_count = ATOMIC_INIT(0);

/*
+ * In some cases, like suspend to RAM or hibernation, It might be reasonable
+ * to prohibit probing of devices as it could be unsafe.
+ * Once defer_all_probes is true all drivers probes will be forcibly deferred.
+ */
+static bool defer_all_probes;
+
+/*
* deferred_probe_work_func() - Retry probing devices in the active list.
*/
static void deferred_probe_work_func(struct work_struct *work)
@@ -172,6 +179,30 @@ static void driver_deferred_probe_trigger(void)
}

/**
+ * device_block_probing() - Block/defere device's probes
+ *
+ * It will disable probing of devices and defer their probes instead.
+ */
+void device_block_probing(void)
+{
+ defer_all_probes = true;
+ /* sync with probes to avoid races. */
+ wait_for_device_probe();
+}
+
+/**
+ * device_unblock_probing() - Unblock/enable device's probes
+ *
+ * It will restore normal behavior and trigger re-probing of deferred
+ * devices.
+ */
+void device_unblock_probing(void)
+{
+ defer_all_probes = false;
+ driver_deferred_probe_trigger();
+}
+
+/**
* deferred_probe_initcall() - Enable probing of deferred devices
*
* We don't want to get in the way when the bulk of drivers are getting probed.
@@ -279,9 +310,20 @@ static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);

static int really_probe(struct device *dev, struct device_driver *drv)
{
- int ret = 0;
+ int ret = -EPROBE_DEFER;
int local_trigger_count = atomic_read(&deferred_trigger_count);

+ if (defer_all_probes) {
+ /*
+ * Value of defer_all_probes can be set only by
+ * device_defer_all_probes_enable() which, in turn, will call
+ * wait_for_device_probe() right after that to avoid any races.
+ */
+ dev_dbg(dev, "Driver %s force probe deferral\n", drv->name);
+ driver_deferred_probe_add(dev);
+ return ret;
+ }
+
atomic_inc(&probe_count);
pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
drv->bus->name, __func__, drv->name, dev_name(dev));
@@ -387,6 +429,10 @@ int driver_probe_done(void)
*/
void wait_for_device_probe(void)
{
+ /* wait for the deferred probe workqueue to finish */
+ if (driver_deferred_probe_enable)
+ flush_workqueue(deferred_wq);
+
/* wait for the known devices to complete their probing */
wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
async_synchronize_full();
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 6c5bc3f..cf4384d 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -966,6 +966,9 @@ void dpm_complete(pm_message_t state)
}
list_splice(&list, &dpm_list);
mutex_unlock(&dpm_list_mtx);
+
+ /* Allow device probing and trigger re-probing of deferred devices */
+ device_unblock_probing();
trace_suspend_resume(TPS("dpm_complete"), state.event, false);
}

@@ -1638,6 +1641,20 @@ int dpm_prepare(pm_message_t state)
trace_suspend_resume(TPS("dpm_prepare"), state.event, true);
might_sleep();

+ /*
+ * Give a chance for the known devices to complete their probes, before
+ * disable probing of devices. This sync point is important at least
+ * at boot time + hibernation restore.
+ */
+ wait_for_device_probe();
+ /*
+ * It is unsafe if probing of devices will happen during suspend or
+ * hibernation and system behavior will be unpredictable in this case.
+ * So, let's prohibit device's probing here and defer their probes
+ * instead. The normal behavior will be restored in dpm_complete().
+ */
+ device_block_probing();
+
mutex_lock(&dpm_list_mtx);
while (!list_empty(&dpm_list)) {
struct device *dev = to_device(dpm_list.next);
--
1.9.1