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Subject: Re: [PATCH] mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC
To:     Souptick Joarder <jrdr.linux@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>, linux-kernel@vger.kernel.org
References: <20190225191710.48131-1-cai@lca.pw>
 <CAFqt6zYjf=KnXhkmbr78RR3ZkzRmTaERJMNOn7CXrrYYxrV-Pg@mail.gmail.com>
From:   Qian Cai <cai@lca.pw>
Message-ID: <509cbfb1-d10e-0078-0722-766bbec5460e@lca.pw>
Date:   Tue, 26 Feb 2019 09:07:03 -0500
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On 2/26/19 7:13 AM, Souptick Joarder wrote:
> On Tue, Feb 26, 2019 at 12:47 AM Qian Cai <cai@lca.pw> wrote:
>>
>> When onlining memory pages, it calls kernel_unmap_linear_page(),
>> However, it does not call kernel_map_linear_page() while offlining
>> memory pages. As the result, it triggers a panic below while onlining on
>> ppc64le as it checks if the pages are mapped before unmapping,
>> Therefore, let it call kernel_map_linear_page() when setting all pages
>> as reserved.
>>
>> kernel BUG at arch/powerpc/mm/hash_utils_64.c:1815!
>> Oops: Exception in kernel mode, sig: 5 [#1]
>> LE SMP NR_CPUS=256 DEBUG_PAGEALLOC NUMA pSeries
>> CPU: 2 PID: 4298 Comm: bash Not tainted 5.0.0-rc7+ #15
>> NIP:  c000000000062670 LR: c00000000006265c CTR: 0000000000000000
>> REGS: c0000005bf8a75b0 TRAP: 0700   Not tainted  (5.0.0-rc7+)
>> MSR:  800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 28422842  XER: 00000000
>> CFAR: c000000000804f44 IRQMASK: 1
>> GPR00: c00000000006265c c0000005bf8a7840 c000000001518200 c0000000013cbcc8
>> GPR04: 0000000000080004 0000000000000000 00000000ccc457e0 c0000005c4e341d8
>> GPR08: 0000000000000000 0000000000000001 c000000007f4f800 0000000000000001
>> GPR12: 0000000000002200 c000000007f4e100 0000000000000000 0000000139c29710
>> GPR16: 0000000139c29714 0000000139c29788 c0000000013cbcc8 0000000000000000
>> GPR20: 0000000000034000 c0000000016e05e8 0000000000000000 0000000000000001
>> GPR24: 0000000000bf50d9 800000000000018e 0000000000000000 c0000000016e04b8
>> GPR28: f000000000d00040 0000006420a2f217 f000000000d00000 00ea1b2170340000
>> NIP [c000000000062670] __kernel_map_pages+0x2e0/0x4f0
>> LR [c00000000006265c] __kernel_map_pages+0x2cc/0x4f0
>> Call Trace:
>> [c0000005bf8a7840] [c00000000006265c] __kernel_map_pages+0x2cc/0x4f0 (unreliable)
>> [c0000005bf8a78d0] [c00000000028c4a0] free_unref_page_prepare+0x2f0/0x4d0
>> [c0000005bf8a7930] [c000000000293144] free_unref_page+0x44/0x90
>> [c0000005bf8a7970] [c00000000037af24] __online_page_free+0x84/0x110
>> [c0000005bf8a79a0] [c00000000037b6e0] online_pages_range+0xc0/0x150
>> [c0000005bf8a7a00] [c00000000005aaa8] walk_system_ram_range+0xc8/0x120
>> [c0000005bf8a7a50] [c00000000037e710] online_pages+0x280/0x5a0
>> [c0000005bf8a7b40] [c0000000006419e4] memory_subsys_online+0x1b4/0x270
>> [c0000005bf8a7bb0] [c000000000616720] device_online+0xc0/0xf0
>> [c0000005bf8a7bf0] [c000000000642570] state_store+0xc0/0x180
>> [c0000005bf8a7c30] [c000000000610b2c] dev_attr_store+0x3c/0x60
>> [c0000005bf8a7c50] [c0000000004c0a50] sysfs_kf_write+0x70/0xb0
>> [c0000005bf8a7c90] [c0000000004bf40c] kernfs_fop_write+0x10c/0x250
>> [c0000005bf8a7ce0] [c0000000003e4b18] __vfs_write+0x48/0x240
>> [c0000005bf8a7d80] [c0000000003e4f68] vfs_write+0xd8/0x210
>> [c0000005bf8a7dd0] [c0000000003e52f0] ksys_write+0x70/0x120
>> [c0000005bf8a7e20] [c00000000000b000] system_call+0x5c/0x70
>> Instruction dump:
>> 7fbd5278 7fbd4a78 3e42ffeb 7bbd0640 3a523ac8 7e439378 487a2881 60000000
>> e95505f0 7e6aa0ae 6a690080 7929c9c2 <0b090000> 7f4aa1ae 7e439378 487a28dd
>>
>> Signed-off-by: Qian Cai <cai@lca.pw>
>> ---
>>  mm/page_alloc.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 10d0f2ed9f69..025fc93d1518 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -8349,6 +8349,7 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
>>                 for (i = 0; i < (1 << order); i++)
>>                         SetPageReserved((page+i));
>>                 pfn += (1 << order);
>> +               kernel_map_pages(page, 1 << order, 1);
> 
> Doubt , Not sure, but does this change will have any impact on
> drivers/base/memory.c#L249
> memory_block_action() ->  offline_pages() ?

Yes, it does.