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Date: Fri, 7 Jan 2022 17:19:59 -0800
From: Matthias Kaehlcke <mka@...omium.org>
To: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>,
Andy Gross <agross@...nel.org>,
Ohad Ben-Cohen <ohad@...ery.com>,
Stephen Boyd <swboyd@...omium.org>,
Sibi Sankar <sibis@...eaurora.org>,
Sujit Kautkar <sujitka@...omium.org>,
linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] rpmsg: char: Fix race between the release of
rpmsg_ctrldev and cdev
On Fri, Jan 07, 2022 at 03:57:50PM -0800, Bjorn Andersson wrote:
> On Fri 07 Jan 11:44 PST 2022, Matthias Kaehlcke wrote:
>
> > On Mon, Dec 13, 2021 at 10:32:07AM -0700, Mathieu Poirier wrote:
> > > On Wed, Dec 08, 2021 at 12:52:28PM -0800, Matthias Kaehlcke wrote:
> > > > From: Sujit Kautkar <sujitka@...omium.org>
> > > >
> > > > From: Sujit Kautkar <sujitka@...omium.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@...omium.org>
> > > > Signed-off-by: Matthias Kaehlcke <mka@...omium.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);
> > >
> > > Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > >
> > > I'll let Bjorn pick this one to make sure it doesn't break anything for current
> > > users of the driver.
> >
> > Bjorn: can this land or is there any action pending on my side?
>
> Thanks for the ping Mathieu, this looks good to me, so:
>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>
> But it should come with:
>
> Fixes: c0cdc19f84a4 ("rpmsg: Driver for user space endpoint interface")
Thanks, will add!
> But afaict we have the exact same problem in rpmsg_eptdev_create(), is
> there a reason why this isn't updated as well?
Because I didn't notice :)
I'll fix it too, not sure yet if in the same patch or a separate one.
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