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[104.57.184.186]) by smtp.gmail.com with ESMTPSA id m5sm212638oon.45.2021.11.17.15.29.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Nov 2021 15:29:11 -0800 (PST) Date: Wed, 17 Nov 2021 17:29:07 -0600 From: Bjorn Andersson To: Sujit Kautkar Cc: Andy Gross , Ohad Ben-Cohen , Sibi Sankar , Matthias Kaehlcke , Stephen Boyd , linux-kernel@vger.kernel.org, linux-remoteproc@vger.kernel.org Subject: Re: [PATCH v3 2/2] rpmsg: glink: Update cdev add/del API in rpmsg_ctrldev_release_device() Message-ID: References: <20211102235147.872921-1-sujitka@chromium.org> <20211102165137.v3.2.Ie09561c5b453a91f10ecc7e1974c602c4ff78245@changeid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211102165137.v3.2.Ie09561c5b453a91f10ecc7e1974c602c4ff78245@changeid> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 02 Nov 18:51 CDT 2021, Sujit Kautkar wrote: I like Stephen's suggestion about modifying the $subject. Also note that the change isn't in the glink driver, so prefix should reflect that: $ git log --oneline --no-decorate -- drivers/rpmsg/rpmsg_char.c f998d48f9b3c rpmsg: glink: Update cdev add/del API in rpmsg_ctrldev_release_device() bc774a3887cb rpmsg: char: Remove useless include 964e8bedd5a1 rpmsg: char: Return an error if device already open ... > Replace cdev add/del APIs with cdev_device_add/cdev_device_del to avoid > below kernel warning. This correctly takes a reference to the parent > device so the parent will not get released until all references to the > cdev are released. > > | ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x7c > | WARNING: CPU: 7 PID: 19892 at lib/debugobjects.c:488 debug_print_object+0x13c/0x1b0 > | CPU: 7 PID: 19892 Comm: kworker/7:4 Tainted: G W 5.4.147-lockdep #1 > | ================================================================== > | Hardware name: Google CoachZ (rev1 - 2) with LTE (DT) > | Workqueue: events kobject_delayed_cleanup > | pstate: 60c00009 (nZCv daif +PAN +UAO) > | pc : debug_print_object+0x13c/0x1b0 > | lr : debug_print_object+0x13c/0x1b0 > | sp : ffffff83b2ec7970 > | x29: ffffff83b2ec7970 x28: dfffffd000000000 > | x27: ffffff83d674f000 x26: dfffffd000000000 > | x25: ffffffd06b8fa660 x24: dfffffd000000000 > | x23: 0000000000000000 x22: ffffffd06b7c5108 > | x21: ffffffd06d597860 x20: ffffffd06e2c21c0 > | x19: ffffffd06d5974c0 x18: 000000000001dad8 > | x17: 0000000000000000 x16: dfffffd000000000 > | BUG: KASAN: use-after-free in qcom_glink_rpdev_release+0x54/0x70 > | x15: ffffffffffffffff x14: 79616c6564203a74 > | x13: 0000000000000000 x12: 0000000000000080 > | Write of size 8 at addr ffffff83d95768d0 by task kworker/3:1/150 > | x11: 0000000000000001 x10: 0000000000000000 > | x9 : fc9e8edec0ad0300 x8 : fc9e8edec0ad0300 > | > | x7 : 0000000000000000 x6 : 0000000000000000 > | x5 : 0000000000000080 x4 : 0000000000000000 > | CPU: 3 PID: 150 Comm: kworker/3:1 Tainted: G W 5.4.147-lockdep #1 > | x3 : ffffffd06c149574 x2 : ffffff83f77f7498 > | x1 : ffffffd06d596f60 x0 : 0000000000000061 > | Hardware name: Google CoachZ (rev1 - 2) with LTE (DT) > | Call trace: > | debug_print_object+0x13c/0x1b0 > | Workqueue: events kobject_delayed_cleanup > | __debug_check_no_obj_freed+0x25c/0x3c0 > | debug_check_no_obj_freed+0x18/0x20 > | Call trace: > | slab_free_freelist_hook+0xb4/0x1bc > | kfree+0xe8/0x2d8 > | dump_backtrace+0x0/0x27c Why is dump_backtrace in the callstack here inbetween rpmsg_ctrldev_release_device() and kfree()? Isn't the error that we're calling kfree() on an chunk of memory that contains a live object? > | rpmsg_ctrldev_release_device+0x78/0xb8 > | device_release+0x68/0x14c > | show_stack+0x20/0x2c > | kobject_cleanup+0x12c/0x298 > | kobject_delayed_cleanup+0x10/0x18 > | dump_stack+0xe0/0x19c > | process_one_work+0x578/0x92c > | worker_thread+0x804/0xcf8 > | print_address_description+0x3c/0x4a8 > | kthread+0x2a8/0x314 > | ret_from_fork+0x10/0x18 > | __kasan_report+0x100/0x124 > > Signed-off-by: Sujit Kautkar > --- > 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 | 10 ++-------- > 1 file changed, 2 insertions(+), 8 deletions(-) > > diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c > index 876ce43df732b..a6a33155ca859 100644 > --- a/drivers/rpmsg/rpmsg_char.c > +++ b/drivers/rpmsg/rpmsg_char.c > @@ -458,7 +458,7 @@ 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); > + cdev_device_del(&ctrldev->cdev, &ctrldev->dev); I am not able to find any other instance where cdev_device_del() is called from the device's release function itself, which tells me that this probably is not the right thing to do. Instead the appropriate way seem to put the cdev_device_del() in rpmsg_chrdev_remove(). That said, we already do device_del() in rpmsg_chrdev_remove() so if the warning is trying to tell us that ctrldev->dev is not deleted I think we have an unbalanced put_device()? Regards, Bjorn > kfree(ctrldev); > } > > @@ -493,19 +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; > -- > 2.31.0 >