From:   Matthias Kaehlcke <mka@chromium.org>
To:     Andy Gross <agross@kernel.org>, Ohad Ben-Cohen <ohad@wizery.com>
Cc:     Stephen Boyd <swboyd@chromium.org>,
        Sibi Sankar <sibis@codeaurora.org>,
        Sujit Kautkar <sujitka@chromium.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Matthias Kaehlcke <mka@chromium.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>
Subject: [PATCH v4] rpmsg: char: Fix race between the release of rpmsg_ctrldev and cdev
Date:   Wed,  8 Dec 2021 12:52:28 -0800
Message-Id: <20211208125220.v4.1.Iaac908f3e3149a89190ce006ba166e2d3fd247a3@changeid>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Sujit Kautkar <sujitka@chromium.org>

From: Sujit Kautkar <sujitka@chromium.org>

struct rpmsg_ctrldev contains a struct cdev. The current code frees
the rpmsg_ctrldev struct in rpmsg_ctrldev_release_device(), but the
cdev is a managed object, therefore its release is not predictable
and the rpmsg_ctrldev could be freed before the cdev is entirely
released, as in the backtrace below.

[   93.625603] ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x7c
[   93.636115] WARNING: CPU: 0 PID: 12 at lib/debugobjects.c:488 debug_print_object+0x13c/0x1b0
[   93.644799] Modules linked in: veth xt_cgroup xt_MASQUERADE rfcomm algif_hash algif_skcipher af_alg uinput ip6table_nat fuse uvcvideo videobuf2_vmalloc venus_enc venus_dec videobuf2_dma_contig hci_uart btandroid btqca snd_soc_rt5682_i2c bluetooth qcom_spmi_temp_alarm snd_soc_rt5682v
[   93.715175] CPU: 0 PID: 12 Comm: kworker/0:1 Tainted: G    B             5.4.163-lockdep #26
[   93.723855] Hardware name: Google Lazor (rev3 - 8) with LTE (DT)
[   93.730055] Workqueue: events kobject_delayed_cleanup
[   93.735271] pstate: 60c00009 (nZCv daif +PAN +UAO)
[   93.740216] pc : debug_print_object+0x13c/0x1b0
[   93.744890] lr : debug_print_object+0x13c/0x1b0
[   93.749555] sp : ffffffacf5bc7940
[   93.752978] x29: ffffffacf5bc7940 x28: dfffffd000000000
[   93.758448] x27: ffffffacdb11a800 x26: dfffffd000000000
[   93.763916] x25: ffffffd0734f856c x24: dfffffd000000000
[   93.769389] x23: 0000000000000000 x22: ffffffd0733c35b0
[   93.774860] x21: ffffffd0751994a0 x20: ffffffd075ec27c0
[   93.780338] x19: ffffffd075199100 x18: 00000000000276e0
[   93.785814] x17: 0000000000000000 x16: dfffffd000000000
[   93.791291] x15: ffffffffffffffff x14: 6e6968207473696c
[   93.796768] x13: 0000000000000000 x12: ffffffd075e2b000
[   93.802244] x11: 0000000000000001 x10: 0000000000000000
[   93.807723] x9 : d13400dff1921900 x8 : d13400dff1921900
[   93.813200] x7 : 0000000000000000 x6 : 0000000000000000
[   93.818676] x5 : 0000000000000080 x4 : 0000000000000000
[   93.824152] x3 : ffffffd0732a0fa4 x2 : 0000000000000001
[   93.829628] x1 : ffffffacf5bc7580 x0 : 0000000000000061
[   93.835104] Call trace:
[   93.837644]  debug_print_object+0x13c/0x1b0
[   93.841963]  __debug_check_no_obj_freed+0x25c/0x3c0
[   93.846987]  debug_check_no_obj_freed+0x18/0x20
[   93.851669]  slab_free_freelist_hook+0xbc/0x1e4
[   93.856346]  kfree+0xfc/0x2f4
[   93.859416]  rpmsg_ctrldev_release_device+0x78/0xb8
[   93.864445]  device_release+0x84/0x168
[   93.868310]  kobject_cleanup+0x12c/0x298
[   93.872356]  kobject_delayed_cleanup+0x10/0x18
[   93.876948]  process_one_work+0x578/0x92c
[   93.881086]  worker_thread+0x804/0xcf8
[   93.884963]  kthread+0x2a8/0x314
[   93.888303]  ret_from_fork+0x10/0x18

The cdev_device_add/del() API was created to address this issue
(see commit 233ed09d7fda), use it instead of cdev add/del().

Signed-off-by: Sujit Kautkar <sujitka@chromium.org>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---

Changes in v4:
- call cdev_device_del() from rpmsg_chrdev_remove() instead of
  rpmsg_ctrldev_release_device()
- updated subject (was: "rpmsg: glink: Update cdev add/del API in
  rpmsg_ctrldev_release_device()")
- updated commit message
- replaced backtrace in commit message with one that doesn't have
  a dump_backtrace() call

Changes in v3:
- Remove unecessary error check as per Matthias's comment

Changes in v2:
- Fix typo in commit message

 drivers/rpmsg/rpmsg_char.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index b5907b80727c..b1b75ef04560 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -459,7 +459,6 @@ static void rpmsg_ctrldev_release_device(struct device *dev)
 
 	ida_simple_remove(&rpmsg_ctrl_ida, dev->id);
 	ida_simple_remove(&rpmsg_minor_ida, MINOR(dev->devt));
-	cdev_del(&ctrldev->cdev);
 	kfree(ctrldev);
 }
 
@@ -494,19 +493,13 @@ static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
 	dev->id = ret;
 	dev_set_name(&ctrldev->dev, "rpmsg_ctrl%d", ret);
 
-	ret = cdev_add(&ctrldev->cdev, dev->devt, 1);
+	ret = cdev_device_add(&ctrldev->cdev, &ctrldev->dev);
 	if (ret)
 		goto free_ctrl_ida;
 
 	/* We can now rely on the release function for cleanup */
 	dev->release = rpmsg_ctrldev_release_device;
 
-	ret = device_add(dev);
-	if (ret) {
-		dev_err(&rpdev->dev, "device_add failed: %d\n", ret);
-		put_device(dev);
-	}
-
 	dev_set_drvdata(&rpdev->dev, ctrldev);
 
 	return ret;
@@ -532,7 +525,7 @@ static void rpmsg_chrdev_remove(struct rpmsg_device *rpdev)
 	if (ret)
 		dev_warn(&rpdev->dev, "failed to nuke endpoints: %d\n", ret);
 
-	device_del(&ctrldev->dev);
+	cdev_device_del(&ctrldev->cdev, &ctrldev->dev);
 	put_device(&ctrldev->dev);
 }
 
-- 
2.34.1.400.ga245620fadb-goog