linux-kernel - Re: next: runtime warning after 'locking/refcounts: Out-of-line everything'

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Message-ID: <5cf8e510-ead0-7aa8-3e3a-f6b2870ce744@roeck-us.net>
Date:   Tue, 28 Feb 2017 07:05:29 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: next: runtime warning after 'locking/refcounts: Out-of-line
 everything'

On 02/27/2017 11:52 PM, Peter Zijlstra wrote:
> On Mon, Feb 27, 2017 at 01:47:47PM -0800, Guenter Roeck wrote:
>> Hi Peter,
>>
>> I see the following runtime warning when running a 44x/virtex5_defconfig
>> image in qemu (virtex-ml507).
>>
>> refcount_t: underflow; use-after-free.
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 1 at lib/refcount.c:128 refcount_sub_and_test+0x90/0xd0
>> Modules linked in:
>> CPU: 0 PID: 1 Comm: swapper Not tainted 4.10.0-next-20170227 #1
>> task: cf81d5a0 task.stack: cf81e000
>> NIP: c02100e0 LR: c02100e0 CTR: c0279970
>> REGS: cf81fc90 TRAP: 0700   Not tainted  (4.10.0-next-20170227)
>> MSR: 00029000 <CE,EE,ME>
>> CR: 24000022  XER: 00000000
>>
>> GPR00: c02100e0 cf81fd40 cf81d5a0 00000026 00000000 00000000 c027a3d0 00000000
>> GPR08: c05403bc 00000800 00000000 00000000 24000024 00000000 c0001ad0 00000000
>> GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 c054b3c0 c0550000
>> GPR24: 00000000 00000000 cf948010 00000015 00000000 00000000 cf948000 cfb1c0e8
>> NIP [c02100e0] refcount_sub_and_test+0x90/0xd0
>> LR [c02100e0] refcount_sub_and_test+0x90/0xd0
>> Call Trace:
>> [cf81fd40] [c02100e0] refcount_sub_and_test+0x90/0xd0 (unreliable)
>> [cf81fd50] [c01f6564] kobject_put+0x34/0x90
>> [cf81fd60] [c02ac240] ace_probe+0x410/0x450
>> [cf81fda0] [c0293684] platform_drv_probe+0x44/0xc0
>> [cf81fdc0] [c0291494] driver_probe_device+0x234/0x340
>> [cf81fdf0] [c029166c] __driver_attach+0xcc/0xd0
>> [cf81fe10] [c028eff8] bus_for_each_dev+0x68/0xc0
>> [cf81fe40] [c0290838] bus_add_driver+0x208/0x280
>> [cf81fe60] [c0292198] driver_register+0x88/0x140
>> [cf81fe70] [c050be10] ace_init+0x48/0xa4
>> [cf81fe90] [c0001350] do_one_initcall+0x40/0x180
>> [cf81fef0] [c04f2ae0] kernel_init_freeable+0x134/0x1cc
>> [cf81ff30] [c0001ae4] kernel_init+0x14/0x110
>> [cf81ff40] [c000c3d0] ret_from_kernel_thread+0x5c/0x64
>> Instruction dump:
>> 40a2fff0 7f884840 7d094378 419e0044 2f89ffff 7d434850 7f0a4840 419e0018
>> 4099ffd0 3c60c04b 386393f0 4820e99d <0fe00000> 80010014 38600000 38210010
>> ---[ end trace 17bd7014e44a5b26 ]---
>> xsysace 83600000.sysace: xsysace: error initializing device at 0x83600000
>> xsysace 83600000.sysace: could not initialize device, err=-12
>> xsysace: probe of 83600000.sysace failed with error -12
>> Xilinx SystemACE device driver, major=254
>>
>> The complete log is available at
>> http://kerneltests.org/builders/qemu-ppc-next/builds/590/steps/qemubuildcommand/logs/stdio
>>
>> Bisect points to commit 29dee3c03abc ("locking/refcounts: Out-of-line
>> everything'); bisect log is attached. Reverting this commit fixes the problem.
>>
>> Please let me know if there is anything I can do to help tracking down the
>> problem.
>>
>> [ Maybe there is a bug in the ace driver's error handler, but why is it only
>>   seen with your patch applied ? ]
>
> Because it unconditionally enables the WARNs, if you revert but enable
> CONFIG_DEBUG_REFCOUNT it should show up as well.
>

Good point. I'll try to find out what is wrong with that driver.

Thanks,
Guenter