Re: [PATCH] mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC

[Souptick Joarder]

On Tue, Feb 26, 2019 at 12:47 AM Qian Cai <cai@xxxxxx> 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@xxxxxx>
> ---
>  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() ?

>         }
>         spin_unlock_irqrestore(&zone->lock, flags);
>  }
> --
> 2.17.2 (Apple Git-113)
>