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Subject: Re: [PATCH] mm: check for memory's node later during boot
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-mm@kvack.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        nathanl@linux.ibm.com, cheloha@linux.ibm.com,
        "Rafael J. Wysocki" <rafael@kernel.org>
References: <20200902090911.11363-1-ldufour@linux.ibm.com>
 <20200903143523.02e163bf06be3b48bac7f967@linux-foundation.org>
From:   Laurent Dufour <ldufour@linux.ibm.com>
Message-ID: <2abef8b6-932d-2aac-68d0-e8d202aab76e@linux.ibm.com>
Date:   Tue, 8 Sep 2020 08:56:08 +0200
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Le 03/09/2020 à 23:35, Andrew Morton a écrit :
> On Wed,  2 Sep 2020 11:09:11 +0200 Laurent Dufour <ldufour@linux.ibm.com> wrote:
> 
>> register_mem_sect_under_nodem() is checking the memory block's node id only
>> if the system state is "SYSTEM_BOOTING". On PowerPC, the memory blocks are
>> registered while the system state is "SYSTEM_SCHEDULING", the one before
>> SYSTEM_RUNNING.
>>
>> The consequence on PowerPC guest with interleaved memory node's ranges is
>> that some memory block could be assigned to multiple nodes on sysfs. This
>> lately prevents some memory hot-plug and hot-unplug to succeed because
>> links are remaining. Such a panic is then displayed:
>>
>> ------------[ cut here ]------------
>> kernel BUG at /Users/laurent/src/linux-ppc/mm/memory_hotplug.c:1084!
>> Oops: Exception in kernel mode, sig: 5 [#1]
>> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
>> Modules linked in: rpadlpar_io rpaphp pseries_rng rng_core vmx_crypto gf128mul binfmt_misc ip_tables x_tables xfs libcrc32c crc32c_vpmsum autofs4
>> CPU: 8 PID: 10256 Comm: drmgr Not tainted 5.9.0-rc1+ #25
>> NIP:  c000000000403f34 LR: c000000000403f2c CTR: 0000000000000000
>> REGS: c0000004876e3660 TRAP: 0700   Not tainted  (5.9.0-rc1+)
>> MSR:  800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 24000448  XER: 20040000
>> CFAR: c000000000846d20 IRQMASK: 0
>> GPR00: c000000000403f2c c0000004876e38f0 c0000000012f6f00 ffffffffffffffef
>> GPR04: 0000000000000227 c0000004805ae680 0000000000000000 00000004886f0000
>> GPR08: 0000000000000226 0000000000000003 0000000000000002 fffffffffffffffd
>> GPR12: 0000000088000484 c00000001ec96280 0000000000000000 0000000000000000
>> GPR16: 0000000000000000 0000000000000000 0000000000000004 0000000000000003
>> GPR20: c00000047814ffe0 c0000007ffff7c08 0000000000000010 c0000000013332c8
>> GPR24: 0000000000000000 c0000000011f6cc0 0000000000000000 0000000000000000
>> GPR28: ffffffffffffffef 0000000000000001 0000000150000000 0000000010000000
>> NIP [c000000000403f34] add_memory_resource+0x244/0x340
>> LR [c000000000403f2c] add_memory_resource+0x23c/0x340
>> Call Trace:
>> [c0000004876e38f0] [c000000000403f2c] add_memory_resource+0x23c/0x340 (unreliable)
>> [c0000004876e39c0] [c00000000040408c] __add_memory+0x5c/0xf0
>> [c0000004876e39f0] [c0000000000e2b94] dlpar_add_lmb+0x1b4/0x500
>> [c0000004876e3ad0] [c0000000000e3888] dlpar_memory+0x1f8/0xb80
>> [c0000004876e3b60] [c0000000000dc0d0] handle_dlpar_errorlog+0xc0/0x190
>> [c0000004876e3bd0] [c0000000000dc398] dlpar_store+0x198/0x4a0
>> [c0000004876e3c90] [c00000000072e630] kobj_attr_store+0x30/0x50
>> [c0000004876e3cb0] [c00000000051f954] sysfs_kf_write+0x64/0x90
>> [c0000004876e3cd0] [c00000000051ee40] kernfs_fop_write+0x1b0/0x290
>> [c0000004876e3d20] [c000000000438dd8] vfs_write+0xe8/0x290
>> [c0000004876e3d70] [c0000000004391ac] ksys_write+0xdc/0x130
>> [c0000004876e3dc0] [c000000000034e40] system_call_exception+0x160/0x270
>> [c0000004876e3e20] [c00000000000d740] system_call_common+0xf0/0x27c
>> Instruction dump:
>> 48442e35 60000000 0b030000 3cbe0001 7fa3eb78 7bc48402 38a5fffe 7ca5fa14
>> 78a58402 48442db1 60000000 7c7c1b78 <0b030000> 7f23cb78 4bda371d 60000000
>> ---[ end trace 562fd6c109cd0fb2 ]---
>>
>> To prevent this multiple links, make the node checking done for states
>> prior to SYSTEM_RUNNING.
> 
> Did you consider adding a cc:stable to this fix?

I should have, but now I've to review the fix based on David's comment.