linux-kernel - [PATCH v1 1/3] driver core: Don't do deferred probe in parallel with kernel

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Date:   Wed,  1 Jul 2020 12:42:57 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        kernel-team@...roid.com
Subject: [PATCH v1 1/3] driver core: Don't do deferred probe in parallel with
 kernel_init thread

The current deferred probe implementation can mess up suspend/resume
ordering if deferred probe thread is kicked off in parallel with the
main initcall thread (kernel_init thread) [1].

For example:

Say device-B is a consumer of device-A.

Initcall thread					Deferred probe thread
===============					=====================
1. device-A is added.
2. device-B is added.
3. dpm_list is now [device-A, device-B].
4. driver-A defers probe of device-A.
						5. device-A is moved to
						   end of dpm_list
						6. dpm_list is now
						   [device-B, device-A]
7. driver-B is registereed and probes device-B.
8. dpm_list stays as [device-B, device-A].

The reverse order of dpm_list is used for suspend. So in this case
device-A would incorrectly get suspended before device-B.

Commit 716a7a259690 ("driver core: fw_devlink: Add support for batching
fwnode parsing") kicked off the deferred probe thread early during boot
to run in parallel with the initcall thread and caused suspend/resume
regressions.  This patch removes the parallel run of the deferred probe
thread to avoid the suspend/resume regressions.

[1] - https://lore.kernel.org/lkml/CAGETcx8W96KAw-d_siTX4qHB_-7ddk0miYRDQeHE6E0_8qx-6Q@mail.gmail.com/

Fixes: 716a7a259690 ("driver core: fw_devlink: Add support for batching fwnode parsing")
Signed-off-by: Saravana Kannan <saravanak@...gle.com>
---
 drivers/base/base.h | 1 -
 drivers/base/core.c | 1 -
 drivers/base/dd.c   | 5 -----
 3 files changed, 7 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index 95c22c0f9036..40fb069a8a7e 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -153,7 +153,6 @@ 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);
-extern void driver_deferred_probe_force_trigger(void);
 
 /* /sys/devices directory */
 extern struct kset *devices_kset;
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 67d39a90b45c..35cc9896eb9e 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1323,7 +1323,6 @@ void fw_devlink_resume(void)
 		goto out;
 
 	device_link_add_missing_supplier_links();
-	driver_deferred_probe_force_trigger();
 out:
 	mutex_unlock(&defer_fw_devlink_lock);
 }
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 9a1d940342ac..48ca81cb8ebc 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -164,11 +164,6 @@ static void driver_deferred_probe_trigger(void)
 	if (!driver_deferred_probe_enable)
 		return;
 
-	driver_deferred_probe_force_trigger();
-}
-
-void driver_deferred_probe_force_trigger(void)
-{
 	/*
 	 * A successful probe means that all the devices in the pending list
 	 * should be triggered to be reprobed.  Move all the deferred devices
-- 
2.27.0.212.ge8ba1cc988-goog