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Date:   Wed, 15 Jul 2020 22:08:46 -0700
Message-Id: <20200716050846.2047110-1-saravanak@google.com>
Mime-Version: 1.0
Subject: [PATCH v1] driver core: Fix scheduling while atomic warnings during
 device link deletion
From:   Saravana Kannan <saravanak@google.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Saravana Kannan <saravanak@google.com>
Cc:     Marek Szyprowski <m.szyprowski@samsung.com>,
        Guenter Roeck <linux@roeck-us.net>, kernel-team@android.com,
        linux-kernel@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Marek and Guenter reported that commit 287905e68dd2 ("driver core:
Expose device link details in sysfs") caused sleeping/scheduling while
atomic warnings.

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:935
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 12, name: kworker/0:1
2 locks held by kworker/0:1/12:
  #0: ee8074a8 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x174/0x7dc
  #1: ee921f20 ((work_completion)(&sdp->work)){+.+.}-{0:0}, at: process_one_work+0x174/0x7dc
Preemption disabled at:
[<c01b10f0>] srcu_invoke_callbacks+0xc0/0x154
----- 8< ----- SNIP
[<c064590c>] (device_del) from [<c0645c9c>] (device_unregister+0x24/0x64)
[<c0645c9c>] (device_unregister) from [<c01b10fc>] (srcu_invoke_callbacks+0xcc/0x154)
[<c01b10fc>] (srcu_invoke_callbacks) from [<c01493c4>] (process_one_work+0x234/0x7dc)
[<c01493c4>] (process_one_work) from [<c01499b0>] (worker_thread+0x44/0x51c)
[<c01499b0>] (worker_thread) from [<c0150bf4>] (kthread+0x158/0x1a0)
[<c0150bf4>] (kthread) from [<c0100114>] (ret_from_fork+0x14/0x20)
Exception stack(0xee921fb0 to 0xee921ff8)

This was caused by the device link device being released in the context
of srcu_invoke_callbacks().  There is no need to wait till the RCU
callback to release the device link device.  So release the device
earlier and revert the RCU callback code to what it was before
commit 287905e68dd2 ("driver core: Expose device link details in sysfs")

Fixes: 287905e68dd2 ("driver core: Expose device link details in sysfs")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Saravana Kannan <saravanak@google.com>
---
Marek and Guenter,

It haven't had a chance to test this yet. Can one of you please test it
and confirm it fixes the issue?

Thanks,
Saravana

 drivers/base/core.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 5373ddd029f6..ccb2ce11f5b5 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -306,16 +306,10 @@ static struct attribute *devlink_attrs[] = {
 };
 ATTRIBUTE_GROUPS(devlink);
 
-static void devlink_dev_release(struct device *dev)
-{
-	kfree(to_devlink(dev));
-}
-
 static struct class devlink_class = {
 	.name = "devlink",
 	.owner = THIS_MODULE,
 	.dev_groups = devlink_groups,
-	.dev_release = devlink_dev_release,
 };
 
 static int devlink_add_symlinks(struct device *dev,
@@ -737,7 +731,7 @@ static void device_link_free(struct device_link *link)
 
 	put_device(link->consumer);
 	put_device(link->supplier);
-	device_unregister(&link->link_dev);
+	kfree(link);
 }
 
 #ifdef CONFIG_SRCU
@@ -756,6 +750,7 @@ static void __device_link_del(struct kref *kref)
 	if (link->flags & DL_FLAG_PM_RUNTIME)
 		pm_runtime_drop_link(link->consumer);
 
+	device_unregister(&link->link_dev);
 	list_del_rcu(&link->s_node);
 	list_del_rcu(&link->c_node);
 	call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
@@ -771,6 +766,7 @@ static void __device_link_del(struct kref *kref)
 	if (link->flags & DL_FLAG_PM_RUNTIME)
 		pm_runtime_drop_link(link->consumer);
 
+	device_unregister(&link->link_dev);
 	list_del(&link->s_node);
 	list_del(&link->c_node);
 	device_link_free(link);
-- 
2.28.0.rc0.105.gf9edc3c819-goog