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Subject: Re: [PATCH v1] driver core: Fix scheduling while atomic warnings
 during device link deletion
To:     Guenter Roeck <linux@roeck-us.net>,
        Saravana Kannan <saravanak@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     kernel-team@android.com, linux-kernel@vger.kernel.org
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-ID: <99bf8e73-1daa-34b8-ca7e-093a44fdba9b@samsung.com>
Date:   Thu, 16 Jul 2020 07:48:42 +0200
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References: <20200716050846.2047110-1-saravanak@google.com>
        <CGME20200716053024eucas1p1fc9f469ce40472554cf377e4cd12e1d2@eucas1p1.samsung.com>
        <e3f4469e-8467-1736-8a39-6539b9f542af@roeck-us.net>
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Hi

On 16.07.2020 07:30, Guenter Roeck wrote:
> On 7/15/20 10:08 PM, Saravana Kannan wrote:
>> 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?
>>
> With this patch applied, the original warning is gone, but I get lots
> of other warnings.
>
> WARNING: CPU: 0 PID: 1 at drivers/base/core.c:1790 device_release+0x94/0xa4^M
> Device 'regulators:regulator@0:50038000.ethernet' does not have a release() function, it is broken and must be fixed.
>
> WARNING: CPU: 0 PID: 1 at drivers/base/core.c:1790 device_release+0x94/0xa4
> Device '53f9c000.gpio:50038000.ethernet' does not have a release() function, it is broken and must be fixed.
>
> WARNING: CPU: 0 PID: 1 at drivers/base/core.c:1790 device_release+0x94/0xa4^M
> Device '50030000.tscadc:50030400.tcq' does not have a release() function, it is broken and must be fixed.

I confirm that I also get such warnings for every platform device in the 
system with this patch applied to linux next-20200715:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at drivers/base/core.c:1790 device_release+0x94/0x98
Device '10023c40.power-domain:13620000.sysmmu' does not have a release() 
function, it is broken and must be fixed. See 
Documentation/core-api/kobject.rst.
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 
5.8.0-rc5-next-20200715-00002-g0f637964c4b0 #1270
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c011184c>] (unwind_backtrace) from [<c010d250>] (show_stack+0x10/0x14)
[<c010d250>] (show_stack) from [<c051b8fc>] (dump_stack+0xbc/0xe8)
[<c051b8fc>] (dump_stack) from [<c0126ed8>] (__warn+0xf0/0x108)
[<c0126ed8>] (__warn) from [<c0126f64>] (warn_slowpath_fmt+0x74/0xb8)
[<c0126f64>] (warn_slowpath_fmt) from [<c064a2a0>] 
(device_release+0x94/0x98)
[<c064a2a0>] (device_release) from [<c0522178>] (kobject_put+0x104/0x288)
[<c0522178>] (kobject_put) from [<c064b45c>] (__device_link_del+0x38/0xac)
[<c064b45c>] (__device_link_del) from [<c064c1f0>] 
(device_links_driver_bound+0x260/0x26c)
[<c064c1f0>] (device_links_driver_bound) from [<c0650af0>] 
(driver_bound+0x5c/0x110)
[<c0650af0>] (driver_bound) from [<c0651038>] (really_probe+0x2d4/0x4fc)
[<c0651038>] (really_probe) from [<c06513c8>] 
(driver_probe_device+0x78/0x1fc)
[<c06513c8>] (driver_probe_device) from [<c064ee00>] 
(bus_for_each_drv+0x74/0xb8)
[<c064ee00>] (bus_for_each_drv) from [<c0650cc4>] 
(__device_attach+0xd4/0x16c)
[<c0650cc4>] (__device_attach) from [<c064fdc4>] 
(bus_probe_device+0x88/0x90)
[<c064fdc4>] (bus_probe_device) from [<c064c604>] 
(fw_devlink_resume+0xa0/0x134)
[<c064c604>] (fw_devlink_resume) from [<c102bfd4>] 
(of_platform_default_populate_init+0xa8/0xc0)
[<c102bfd4>] (of_platform_default_populate_init) from [<c0102378>] 
(do_one_initcall+0x8c/0x424)
[<c0102378>] (do_one_initcall) from [<c1001158>] 
(kernel_init_freeable+0x190/0x204)
[<c1001158>] (kernel_init_freeable) from [<c0ac05d0>] 
(kernel_init+0x8/0x118)
[<c0ac05d0>] (kernel_init) from [<c0100114>] (ret_from_fork+0x14/0x20)
Exception stack(0xef0dffb0 to 0xef0dfff8)
ffa0:                                     00000000 00000000 00000000 
00000000
ffc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
00000000
ffe0: 00000000 00000000 00000000 00000000 00000013 00000000
irq event stamp: 40543
hardirqs last  enabled at (40551): [<c019d624>] console_unlock+0x430/0x6cc
hardirqs last disabled at (40568): [<c019d348>] console_unlock+0x154/0x6cc
softirqs last  enabled at (40584): [<c010174c>] __do_softirq+0x50c/0x608
softirqs last disabled at (40595): [<c0130218>] irq_exit+0x168/0x16c
---[ end trace 1d4780a89f63483a ]---

> and so on. I don't know if this is caused by this patch or by
> some other patch in -next.

This is caused by patch 287905e68dd2 ("driver core: Expose device link 
details in sysfs"). If you revert it, the warning will go away.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland