Message-ID: <CACVXFVM+vCpn7Od46bpc5muuu3Nw+ePsoDRSVO3vSn0+WzHFUw@mail.gmail.com>
Date:	Wed, 16 Mar 2016 16:58:22 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Chandra Sekhar Lingutla <clingutla@...eaurora.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-arm-msm@...r.kernel.org,
	Russell King <linux@....linux.org.uk>
Subject: Re: Possible race at user mode helper in request_firmware

On Wed, Mar 16, 2016 at 4:48 PM, Chandra Sekhar Lingutla
<clingutla@...eaurora.org> wrote:
> On 03/16/2016 02:12 PM, Ming Lei wrote:
>>
>> On Wed, Mar 16, 2016 at 3:02 PM, Chandra Sekhar Lingutla
>> <clingutla@...eaurora.org> wrote:
>>>
>>> Hi Ming,
>>>
>>>
>>> On 03/16/2016 07:36 AM, Ming Lei wrote:
>>>>
>>>>
>>>> On Tue, Mar 15, 2016 at 11:09 PM, Ming Lei <ming.lei@...onical.com>
>>>> wrote:
>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> On Mon, Mar 14, 2016 at 8:00 PM,  <clingutla@...eaurora.org> wrote:
>>>>>>
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> I see possible race in _request_firmware_load function, on which I
>>>>>> wanted to
>>>>>> take your opinion.
>>>>>>
>>>>>> When system is going to low power mode, device_cache_fw_images() is
>>>>>> called
>>>>>> from pm notifier which schedules asynchronous workers to cache devices
>>>>>> firmware.
>>>>>> If more than 2 async requests falls under user helper mode, then there
>>>>>> is a
>>>>>> use after free of "firmware" directory kobject.
>>>>>
>>>>>
>>>>>
>>>>> If two requests are for getting same firmware image, only one can be
>>>>> sent
>>>>> out and be completed with user helper, please see
>>>>> fw_lookup_and_allocate_buf(),
>>>>> so the race shouldn't have been triggered in this case.
>>>>>
>>>>> So I guess your test must be involved with at least two different
>>>>> requests.
>>>>>
>>>>>>
>>>>>> The race will hit, when one asynchronous worker calls device_del()
>>>>>> while
>>>>>> other asynchronous worker calls get_device_parent() in
>>>>>> _request_firmware_load().
>>>>>> After loading firmware, first worker calls device_del(), and
>>>>>> "firmware"
>>>>>> directory ref count is 1, so cleanup_glue_dir() calls kobject_put()
>>>>>> with
>>>>>> gdp_mutex lock held.
>>>>>> Meanwhile, second async worker calls device_add(), and
>>>>>> get_device_parent()
>>>>>> is still able to find the firmware directory kobject in ksets after
>>>>>> getting
>>>>>> gdp_mutex.
>>>>>> This kobject gets added as parent to the second device kobject.
>>>>>> By the time of accessing the parent kobject, its ref count was 0 and
>>>>>> prints
>>>>>> below warning stack followed by crash.
>>>>>
>>>>>
>>>>>
>>>>> The trick here is just that we don't use 'struct device' in
>>>>> device_cache_fw_images(),
>>>>> then the firmware device's parent is null during calling device_add()
>>>>> from
>>>>> _request_firmware_load(), but this should be allowed by driver core.
>>>>>
>>>>>   From firmware class view, both device_add()/device_del() is run with
>>>>> pair,
>>>>> and driver core still complains during get_device_parent(), so
>>>>> something
>>>>> inside driver core should be be wrong, IMO.
>>>>
>>>>
>>>>
>>>> Thinking about the issue further, I believe it is a false positive which
>>>> is
>>>> caused by CONFIG_DEBUG_KOBJECT_RELEASE, follows the story:
>>>>
>>>> 1) device_add() path
>>>>
>>>> get_device_parent()
>>>>                  ......
>>>>                  mutex_lock(&gdp_mutex);
>>>>
>>>>                   /* find our class-directory at the parent and
>>>> reference
>>>> it */
>>>>                   spin_lock(&dev->class->p->glue_dirs.list_lock);
>>>>                   list_for_each_entry(k, &dev->class->p->glue_dirs.list,
>>>> entry)
>>>>                           if (k->parent == parent_kobj) {
>>>>                                   kobj = kobject_get(k);
>>>>                                   break;
>>>>                           }
>>>>                   spin_unlock(&dev->class->p->glue_dirs.list_lock);
>>>>                   if (kobj) {
>>>>                           mutex_unlock(&gdp_mutex);
>>>>                           return kobj;
>>>>                   }
>>>>                   k = class_dir_create_and_add(dev->class, parent_kobj);
>>>>                   mutex_unlock(&gdp_mutex);
>>>>                   ......
>>>>
>>>> 2) device_del() path
>>>>
>>>> cleanup_device_parent()
>>>>          ->cleanup_glue_dir()
>>>>               ->mutex_lock(&gdp_mutex);
>>>>               ->kobject_put(glue_dir);
>>>>                      ->kobject_cleanup()
>>>>                            ->kobject_del()
>>>>                                   ->kobj_kset_leave()
>>>>               ->mutex_unlock(&gdp_mutex);
>>>>
>>>> So gdp_mutex is held wrt. both looking up/adding the parent kobject
>>>> and removing the parent kobject. Actually with this lock, both glur_dir
>>>> kobject's referece counting and joining/leaving kset are run atomically.
>>>>
>>>> The race you found is triggered by CONFIG_DEBUG_KOBJECT_RELEASE,
>>>> which causes kobject_cleanup() to be run in workqueue context and the
>>>> lock of gdp_mutex can't be hold in that situation anymore. That is the
>>>> root
>>>> cause for your race.
>>>>
>>>> That also said DEBUG_KOBJECT_RELEASE might cause trouble in
>>>> some situations.
>>>>
>>>> Thanks,
>>>> Ming
>>>>
>>> I agree that, CONFIG_DEBUG_KOBJECT_RELEASE can cause the race, as it
>>> delays
>>> call to kobject_cleanup() which deletes kobj entry in glue_dir list.
>>>
>>> I see the race even after disabling CONFIG_DEBUG_KOBJECT_RELEASE.
>>>
>>> The race is between kobject_put() and kobject_get() for the "firmware"
>>> directory.
>>>
>>> In  device_del() path, I see the race after the call of
>>> cleanup_device_parent().
>>> cleanup_device_parent() calls kobject_put(glue_dir) with gdp_mutex lock
>>> holding,
>>> So ideally, to call kobject_put/kobject_get(glue_dir) we need to acquire
>>> gdp_mutex.
>>>
>>> but kobject_del(kobj) will not hold the gdp_mutex lock while calling
>>> kobject_put(kobj->parent).
>>>
>>> Here is the race:
>>>
>>> Consider 2 async works calls request_firmware() for 2 different binaries
>>> (fw1.bin, fw2.bin)
>>> Async work1 got scheduled first, and it falls in user helper mode so it
>>> creates "firmware" dir
>>> and then creates "fw1.bin" directory to load data from user.
>>> After load completion or timeout, it starts cleanup dir's, meantime async
>>> work2 got scheduled and
>>> it also falls in user helper mode, and story starts here:
>>>
>>> PATH1   req fw for "fw1.bin"
>>> PATH2
>>>   req fw for "fw2.bin"
>>> _request_firmware_load()
>>> device_del(dev1)
>>>
>>>          ->cleanup_device_parent()
>>>
>>>                  mutex_lock(&gdp_mutex);
>>>
>>> _request_firmware_load("fw2.bin")
>>>                  kobject_put(kobj->parent); --> firmware ref ->1
>>>                   ->device_add(dev2)
>>>                  mutex_unlock(&gdp_mutex);
>>> ->get_device_parent()
>>>          ->kobject_del()
>>> mutex_lock(&gdp_mutex)
>>>                  kobj_kset_leave(kobj); -->del "fw1.bin" kobj in kset
>>> list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
>>>                  kobject_put(kobj->parent); /* No lock :)*/
>>> if (k->parent == parent_kobj) {
>>>
>>>                          ->kref_put()    --> firmware ref ->0
>>> kobj = kobject_get(k); -> k is "firmware"
>>>   dir
>>>                                  ->kboject_release()
>>> break;
>>>
>>>                                          ->kobject_del()
>>> }
>>>
>>>                                  /*here deletes firmware entry in kset*/
>>> mutex_unlock(&gdp_mutex)
>>>
>>> ->dev2->kobj.parent = kobj    -> kobj is released already
>>>
>>>
>>>
>>> PATH 1 is started removing the kobject of "fw1.bin" and its parent
>>> "firmware"
>>> .
>>> cleanup_device_parent(dev1) makes firmware ref count to 1, by calling
>>> kobject_put(firmware) with gdp_mutex held.
>>>
>>> and kobject_del(dev1->kobj) will again calls kobject_put(kobj->parent)
>>> without holding gdp_mutex.
>>>
>>> In PATH2, glue_dir is able to find "firmware" kobj, as firmware dir kobj
>>> is
>>> deleted from the glue_dir list at kboject_release().
>>> and it calls kobject_get(firmware), by the time PATH1 calls
>>> kobject_release(firmware).
>>>
>>> So PATH2 got reference of freed firmware kobj and added as parent to
>>> "fw2.bin" kobj.
>>>
>>> I think, here is possible fix for this race:
>>>
>>> ------------------------8<-------------------------------------
>>> Signed-off-by: Lingutla Chandrasekhar <clingutla@...eaurora.org>
>>>
>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>> index 5d8b713..47bc082 100644
>>> --- a/drivers/base/core.c
>>> +++ b/drivers/base/core.c
>>> @@ -1224,7 +1224,13 @@ void device_del(struct device *dev)
>>>                                               BUS_NOTIFY_REMOVED_DEVICE,
>>> dev);
>>>          kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>>>          cleanup_device_parent(dev);
>>> -       kobject_del(&dev->kobj);
>>> +
>>> +       if (dev->kobj.parent->kset == &dev->class->p->glue_dirs) {
>>> +               mutex_lock(&gdp_mutex);
>>> +               kobject_del(&dev->kobj);
>>> +               mutex_unlock(&gdp_mutex);
>>> +       } else
>>> +               kobject_del(&dev->kobj);
>>>          put_device(parent);
>>>   }
>>>   EXPORT_SYMBOL_GPL(device_del);
>>>
>>> --------------------------->8-----------------------------------
>>
>>
>> OK, one simpler way is to move cleanup_device_parent(dev)
>> after kobject_del(&dev->kobj), which looks more clean too.
>>
> No, We can't move that, bcz kobject_del(&dev->kobj) will clear the parent.

Yeah, but I think it is better to do that and just call
cleanup_glue_dir() directly
because cleanup_device_parent() should have released the glue_dir.

BTW, failure path of device_add() has been broken already.

>
>
>>>
>>>
>>>>>
>>>>>>
>>>>>> [21147.455038] ------------[ cut here ]------------
>>>>>> [21147.458910] WARNING: at <...>/kernel/include/linux/kref.h:47
>>>>>> kobject_get+0x50/0x68()
>>>>>> [21147.481199] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>> qcrypto_module(O)
>>>>>> [21147.481256] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>> [21147.481284] Workqueue: events_unbound async_run_entry_fn
>>>>>> [21147.481296] Call trace:
>>>>>> [21147.481315] [<ffffffc000206b60>] dump_backtrace+0x0/0x270
>>>>>> [21147.481331] [<ffffffc000206de0>] show_stack+0x10/0x1c
>>>>>> [21147.481353] [<ffffffc000d569ec>] dump_stack+0x1c/0x28
>>>>>> [21147.481370] [<ffffffc00021cc18>] warn_slowpath_common+0x74/0x9c
>>>>>> [21147.481383] [<ffffffc00021ce4c>] warn_slowpath_null+0x14/0x20
>>>>>> [21147.481397] [<ffffffc000456b10>] kobject_get+0x4c/0x68
>>>>>> [21147.481416] [<ffffffc000609f64>] get_device_parent+0xa0/0x194
>>>>>> [21147.481430] [<ffffffc00060a3f4>] device_add+0x100/0x600
>>>>>> [21147.481446] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>> [21147.481459] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>> [21147.481473] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>> [21147.481490] [<ffffffc00061c65c>]
>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>> [21147.481505] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>> [21147.481521] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>> [21147.481535] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>> [21147.481553] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>> [21147.481563] ---[ end trace dabc98ea48b8ba59 ]---
>>>>>>
>>>>>> [21147.486436] Unable to handle kernel paging request at virtual
>>>>>> address
>>>>>> 0x6b6b6b6b6b6b6bcb
>>>>>> [21147.493816] pgd = ffffffc0a982d000
>>>>>> [21147.498337] [6b6b6b6b6b6b6bcb] *pgd=0000000000000000
>>>>>> [21147.502287] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>>>>>> [21147.507826] Modules linked in: core_ctl(PO) qdrbg_module(O)
>>>>>> qcrypto_module(O)
>>>>>> [21147.514951] CPU: 2 PID: 23935 Comm: kworker/u16:8 Tainted: P W O
>>>>>> 3.10.84-g0957845-00427-g56a05c2 #1
>>>>>> [21147.524686] Workqueue: events_unbound async_run_entry_fn
>>>>>> [21147.529965] task: ffffffc008138000 ti: ffffffc007880000 task.ti:
>>>>>> ffffffc007880000
>>>>>> [21147.537438] PC is at sysfs_create_dir+0x34/0xd4
>>>>>> [21147.541949] LR is at kobject_add_internal+0x120/0x24c
>>>>>> [21147.546979] pc : [<ffffffc000361fa8>] lr : [<ffffffc000456f5c>]
>>>>>> pstate:
>>>>>> 80000145
>>>>>> [21147.996295] Process kworker/u16:8 (pid: 23935, stack limit =
>>>>>> 0xffffffc007880058)
>>>>>> [21148.003673] Call trace:
>>>>>> [21148.006117] [<ffffffc000361fa8>] sysfs_create_dir+0x34/0xd4
>>>>>> [21148.011663] [<ffffffc000456f58>] kobject_add_internal+0x11c/0x24c
>>>>>> [21148.017737] [<ffffffc0004573ec>] kobject_add+0xc8/0xe4
>>>>>> [21148.022863] [<ffffffc00060a410>] device_add+0x11c/0x600
>>>>>> [21148.028069] [<ffffffc00061c390>] _request_firmware+0x8b4/0xa80
>>>>>> [21148.033886] [<ffffffc00061c58c>] request_firmware+0x30/0x3c
>>>>>> [21148.039439] [<ffffffc00061c5ec>] cache_firmware+0x54/0xb0
>>>>>> [21148.044822] [<ffffffc00061c65c>]
>>>>>> __async_dev_cache_fw_image+0x14/0x54
>>>>>> [21148.051249] [<ffffffc000243794>] async_run_entry_fn+0x6c/0x12c
>>>>>> [21148.057064] [<ffffffc000237e88>] process_one_work+0x264/0x3dc
>>>>>> [21148.062792] [<ffffffc0002392c0>] worker_thread+0x1f0/0x340
>>>>>> [21148.068263] [<ffffffc00023e500>] kthread+0xac/0xb8
>>>>>> [21148.073039] Code: b5000094 14000026 d000ac54 9125a294 (7940c281)
>>>>>> [21148.080312] ---[ end trace dabc98ea48b8ba5a ]---
>>>>>>
>>>>>> Below is the callstack where the parent is freed from the slub_debug
>>>>>> info.
>>>>>> 0xFFFFFFC000608D74  \\vmlinux\base/core\class_dir_release+0x0C
>>>>>> 0xFFFFFFC0002FE6BC \\vmlinux\slub\free_debug_processing\fail+0x114
>>>>>> 0xFFFFFFC0002FE7A0 \\vmlinux\slub\__slab_free+0x44
>>>>>> 0xFFFFFFC0002FEE60 \\vmlinux\slub\kfree+0x1F8
>>>>>> 0xFFFFFFC000608D70 \\vmlinux\base/core\class_dir_release+0x8
>>>>>> 0xFFFFFFC000456D70 \\vmlinux\kobject\kobject_release+0x134
>>>>>> 0xFFFFFFC000456E10 \\vmlinux\kobject\kobject_put+0x58
>>>>>> 0xFFFFFFC000456C28 \\vmlinux\kobject\kobject_del+0x64
>>>>>> 0xFFFFFFC000609D78 \\vmlinux\base/core\device_del+0x150
>>>>>> 0xFFFFFFC00061C524
>>>>>> \\vmlinux\firmware_class\_request_firmware\out+0x71C
>>>>>> 0xFFFFFFC00061C58C \\vmlinux\firmware_class\request_firmware+0x30
>>>>>> 0xFFFFFFC00061C5EC \\vmlinux\firmware_class\cache_firmware+0x54
>>>>>> 0xFFFFFFC00061C65C
>>>>>> \\vmlinux\firmware_class\__async_dev_cache_fw_image+0x14
>>>>>> 0xFFFFFFC000243794 \\vmlinux\async\async_run_entry_fn+0x6C
>>>>>> 0xFFFFFFC000237E88 \\vmlinux\workqueue\process_one_work+0x264
>>>>>> 0xFFFFFFC0002392C0 \\vmlinux\workqueue\worker_thread\recheck+0x1A0
>>>>>> 0xFFFFFFC00023E500 \\vmlinux\kthread\kthread+0xAC
>>>>>>
>>>>>> For similar type of issue, I see there is an existing fix: "sysfs:
>>>>>> driver
>>>>>> core: Fix glue dir race condition by gdp_mutex".
>>>>>>
>>>>>>
>>>>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/drivers/base/core.c?id=e4a60d139060975eb956717e4f63ae348d4d8cc5
>>>>>>
>>>>>> Still I am able to reproduce the issue. I have verified this race on
>>>>>> kernels: 3.10, 3.18 and 4.4.
>>>>>>
>>>>>> I followed below procedure to reproduce the issue:
>>>>>>        1. Enable "CONFIG_DEBUG_KOBJECT_RELEASE"
>>>>>>        2. Use test_firmware, modified the test for async calls
>>>>>>        3. Replace WARN_ON with BUG_ON in kref_get().
>>>>>> I ran below script from shell:
>>>>>>       count=0
>>>>>>       while [ 1 ]
>>>>>>       do
>>>>>>               echo 3 >
>>>>>> /sys/devices/virtual/misc/test_firmware/trigger_ufw
>>>>>>               if [ $? -ne 0 ]; then
>>>>>>                       print "Exiting.. "
>>>>>>                       exit 1
>>>>>>               fi
>>>>>>               count=$(($count +1))
>>>>>>               echo "count $count"
>>>>>>        done
>>>>>>
>>>>>> With below patch, I could reproduce the issue in the 2nd iteration.
>>>>>
>>>>>
>>>>>
>>>>> I will run your test script to see if there is new findings.
>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> -------------------------8<----------------------------------------------
>>>>>>
>>>>>> To reproduce the race condition, use firmware test and
>>>>>> CONFIG_DEBUG_KOBJECT_RELEASE=y, which delays kobject
>>>>>> releases. So that we can catch the bug easily.
>>>>>>
>>>>>> Enabled below flags in kernel config file:
>>>>>>
>>>>>> +CONFIG_DEBUG_KOBJECT_RELEASE=y
>>>>>> +CONFIG_TEST_FIRMWARE=y
>>>>>
>>>>>
>>>>>
>>>>> Looks I can't reproduce the issue with your approach.
>>>>>
>>>>>>
>>>>>>
>>>>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
>>>>>> index 484604d..727fb24 100644
>>>>>> --- a/include/linux/kref.h
>>>>>> +++ b/include/linux/kref.h
>>>>>> @@ -44,7 +44,7 @@ static inline void kref_get(struct kref *kref)
>>>>>>         * condition when this kref is freeing by some other thread
>>>>>> right
>>>>>> now.
>>>>>>         * In this case one should use kref_get_unless_zero()
>>>>>>         */
>>>>>> -    WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
>>>>>> +    BUG_ON(atomic_inc_return(&kref->refcount) < 2);
>>>>>>    }
>>>>>>
>>>>>>    /**
>>>>>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>>>>>> old mode 100644
>>>>>> new mode 100755
>>>>>> index 86374c1..14c9598
>>>>>> --- a/lib/test_firmware.c
>>>>>> +++ b/lib/test_firmware.c
>>>>>> @@ -18,6 +18,7 @@
>>>>>>    #include <linux/miscdevice.h>
>>>>>>    #include <linux/slab.h>
>>>>>>    #include <linux/uaccess.h>
>>>>>> +#include <linux/async.h>
>>>>>>
>>>>>> +
>>>>>> +static ASYNC_DOMAIN_EXCLUSIVE(ufw_domain);
>>>>>> +
>>>>>> +static void __async_ufw_work(void *name,
>>>>>> +                                       async_cookie_t cookie)
>>>>>> +{
>>>>>> +    const struct firmware *fw;
>>>>>> +    const char *fw_name = name;
>>>>>> +    int ret;
>>>>>> +
>>>>>> +    pr_err("requesting %s\n", fw_name);
>>>>>> +
>>>>>> +    ret = request_firmware(&fw, fw_name, NULL);
>>>>>> +    pr_err("loaded: %zu\n", fw ? fw->size : 0);
>>>>>> +        if (!ret)
>>>>>> +                kfree(fw);
>>>>>> +
>>>>>> +}
>>>>>> +
>>>>>> +static char *name[] = { "fw1.bin", "fw2.bin"};
>>>>>> +
>>>>>> +static ssize_t trigger_ufw_store(struct device *dev,
>>>>>> +        struct device_attribute *attr,
>>>>>> +        const char *buf, size_t count)
>>>>>> +{
>>>>>> +    int rc, i, c=0;
>>>>>> +    u32 start;
>>>>>> +    char *fw_name;
>>>>>> +
>>>>>> +    rc = kstrtou32(buf, 0, &start);
>>>>>> +    if (rc){
>>>>>> +        pr_err("Invalid option\n");
>>>>>> +        return rc;
>>>>>> +    }
>>>>>> +    pr_err(" no of iterations %d\n", start);
>>>>>> +
>>>>>> +    for (i=0; i< start; i++)
>>>>>> +    {
>>>>>> +        if (c >= 2)
>>>>>> +            c = 0;
>>>>>> +        fw_name = name[c++];
>>>>>> +        async_schedule_domain(__async_ufw_work, (void *)fw_name,
>>>>>> &ufw_domain);
>>>>>> +    }
>>>>>> +    async_synchronize_full_domain(&ufw_domain);
>>>>>> +    return count;
>>>>>> +}
>>>>>>
>>>>>>    static DEVICE_ATTR_WO(trigger_request);
>>>>>> +static DEVICE_ATTR_WO(trigger_ufw);
>>>>>>
>>>>>>    static int __init test_firmware_init(void)
>>>>>>    {
>>>>>> @@ -92,6 +140,12 @@ static int __init test_firmware_init(void)
>>>>>>            goto dereg;
>>>>>>        }
>>>>>>
>>>>>> +    rc = device_create_file(test_fw_misc_device.this_device,
>>>>>> +                             &dev_attr_trigger_ufw);
>>>>>> +    if (rc) {
>>>>>> +        pr_err("could not create sysfs interface: %d\n", rc);
>>>>>> +        goto dereg;
>>>>>> +    }
>>>>>>        pr_warn("interface ready\n");
>>>>>>
>>>>>>        return 0;
>>>>>> @@ -106,7 +160,9 @@ static void __exit test_firmware_exit(void)
>>>>>>    {
>>>>>>        release_firmware(test_firmware);
>>>>>>        device_remove_file(test_fw_misc_device.this_device,
>>>>>> -               &dev_attr_trigger_request);
>>>>>> +            &dev_attr_trigger_request);
>>>>>> +    device_remove_file(test_fw_misc_device.this_device,
>>>>>> +            &dev_attr_trigger_ufw);
>>>>>>        misc_deregister(&test_fw_misc_device);
>>>>>>        pr_warn("removed interface\n");
>>>>>>    }
>>>>>>
>>>>>>
>>>>>>
>>>>>> ----------------------------8<--------------------------------------------
>>>>>>
>>>>>> Thanks and regards,
>>>>>> Chandrasekhar L.
>>>>>> --
>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>> member of
>>>>>> Code Aurora Forum,
>>>>>>    a Linux Foundation Collaborative Project.

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