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Subject: Re: linuxnext-2019119 edac warns (was Re: edac KASAN warning in
 experimental arm64 allmodconfig boot)
To:     Robert Richter <rrichter@marvell.com>
CC:     Borislav Petkov <bp@alien8.de>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        James Morse <james.morse@arm.com>,
        "tony.luck@intel.com" <tony.luck@intel.com>,
        "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        wanghuiqiang <wanghuiqiang@huawei.com>,
        Xiaofei Tan <tanxiaofei@huawei.com>,
        Linuxarm <linuxarm@huawei.com>,
        "Huangming (Mark)" <huangming23@huawei.com>
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From:   John Garry <john.garry@huawei.com>
Message-ID: <4c1bd075-75ec-8445-9595-467b88a406b3@huawei.com>
Date:   Tue, 26 Nov 2019 09:59:05 +0000
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On 22/11/2019 11:28, Robert Richter wrote:
> On 21.11.19 15:23:42, John Garry wrote:
>> On 21/11/2019 14:23, Robert Richter wrote:
>>> On 21.11.19 12:34:22, John Garry wrote:
> 
>>>> [   22.046666] EDAC MC: bug in low-level driver: attempt to assign
>>>> [   22.046666]     duplicate mc_idx 0 in add_mc_to_global_list()
>>>> [   22.058311] ghes_edac: Can't register at EDAC core
>>>> [   22.065402] EDAC MC: bug in low-level driver: attempt to assign
>>>> [   22.065402]     duplicate mc_idx 0 in add_mc_to_global_list()
>>>> [   22.077080] ghes_edac: Can't register at EDAC core
>>>> [   22.084140] EDAC MC: bug in low-level driver: attempt to assign
>>>> [   22.084140]     duplicate mc_idx 0 in add_mc_to_global_list()
>>>> [   22.095789] ghes_edac: Can't register at EDAC core
>>>> [   22.102873] EDAC MC: bug in low-level driver: attempt to assign
>>>> [   22.102873]     duplicate mc_idx 0 in add_mc_to_global_list()
>>>> [   22.115442] ghes_edac: Can't register at EDAC core
>>>> [   22.122536] EDAC MC: bug in low-level driver: attempt to assign
>>>> [   22.122536]     duplicate mc_idx 0 in add_mc_to_global_list()
>>>> [   22.134344] ghes_edac: Can't register at EDAC core
>>>> [   22.141441] EDAC MC: bug in low-level driver: attempt to assign
>>>> [   22.141441]     duplicate mc_idx 0 in add_mc_to_global_list()
>>>> [   22.153089] ghes_edac: Can't register at EDAC core
>>>> [   22.160161] EDAC MC: bug in low-level driver: attempt to assign
>>>> [   22.160161]     duplicate mc_idx 0 in add_mc_to_global_list()
>>>> [   22.171810] ghes_edac: Can't register at EDAC core
>>>
>>> What I am more concerned is this here. In total this implies 8 ghes
>>> users that all try to register a (single-instance) ghes mc device. For
>>> non-x86 only one instance is allowed (see ghes_edac_register(), idx =
>>> 0).
> 
> I also looked into this: With refcount_inc_checked() enabled, the
> refcount is *not* increased from 0 to 1. 

Yeah, I had quickly checked this back then and I think you're right.

Thanks,
John

Under the hood only
> refcount_inc_not_zero() is called instead of refcount_inc(). So the
> refcount is still zero after an edac mc device was registered. Instead
> of sharing the edac mc device, the driver tries to allocate another mc
> device for each GHESv2 entry in the HEST table. This causes the
> 'duplicate mc_idx' message. Also, it is ok to have multiple GHESv2
> entries (your system seems to have 8 entries), e.g. to serve different
> kind of errors in the system.
> 
> Thanks,
> 
> -Robert
> .
>