linux-kernel - Re: [PATCH] mm/autonuma: don't use set_pte

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Date:   Tue, 14 Feb 2017 19:41:17 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     akpm@...ux-foundation.org, Rik van Riel <riel@...riel.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/autonuma: don't use set_pte_at when updating protnone ptes

"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:

> Architectures like ppc64, use privilege access bit to mark pte non accessible.
> This implies that kernel can do a copy_to_user to an address marked for numa fault.
> This also implies that there can be a parallel hardware update for the pte.
> set_pte_at cannot be used in such scenarios. Hence switch the pte
> update to use ptep_get_and_clear and set_pte_at combination.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

With this and other patches a kvm guest is giving me

  494.542145] khugepaged      D13632  1451      2 0x00000800
[  494.542151] Call Trace:
[  494.542158] [c000000fe57a7830] [c000000000e71f10] sysctl_sched_child_runs_first+0x0/0x4 (unreliable)
[  494.542163] [c000000fe57a7a00] [c00000000001ae70] __switch_to+0x2b0/0x440
[  494.542167] [c000000fe57a7a60] [c0000000009ac560] __schedule+0x2e0/0x940
[  494.542170] [c000000fe57a7b00] [c0000000009acc00] schedule+0x40/0xb0
[  494.542173] [c000000fe57a7b30] [c0000000009b1264] rwsem_down_read_failed+0x124/0x1b0
[  494.542176] [c000000fe57a7ba0] [c0000000009b0064] down_read+0x64/0x70
[  494.542180] [c000000fe57a7bd0] [c000000000292a70] khugepaged+0x420/0x25c0
[  494.542184] [c000000fe57a7dc0] [c0000000000df37c] kthread+0x14c/0x190
[  494.542187] [c000000fe57a7e30] [c00000000000bae0] ret_from_kernel_thread+0x5c/0x7c
[  494.542276] INFO: task qemu-system-ppc:6868 blocked for more than 120 seconds.
[  494.542340]       Not tainted 4.10.0-rc8-00025-g0d75d3e #4
[  494.542377] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  494.542439] qemu-system-ppc D10688  6868   6473 0x00040000
[  494.542445] Call Trace:
[  494.542448] [c000000fdca7b6a0] [c00000000001ae70] __switch_to+0x2b0/0x440
[  494.542451] [c000000fdca7b700] [c0000000009ac560] __schedule+0x2e0/0x940
[  494.542454] [c000000fdca7b7a0] [c0000000009acc00] schedule+0x40/0xb0
[  494.542457] [c000000fdca7b7d0] [c0000000009b1264] rwsem_down_read_failed+0x124/0x1b0
[  494.542460] [c000000fdca7b840] [c0000000009b0064] down_read+0x64/0x70
[  494.542464] [c000000fdca7b870] [c0000000002340e0] get_user_pages_unlocked+0x80/0x280
[  494.542467] [c000000fdca7b910] [c0000000002352dc] get_user_pages_fast+0xac/0x110
[  494.542475] [c000000fdca7b960] [d00000001096c4fc] kvmppc_book3s_hv_page_fault+0x2bc/0xbb0 [kvm_hv]
[  494.542479] [c000000fdca7ba50] [d0000000109692e4] kvmppc_vcpu_run_hv+0xee4/0x1290 [kvm_hv]
[  494.542488] [c000000fdca7bb80] [d0000000107113bc] kvmppc_vcpu_run+0x2c/0x40 [kvm]
[  494.542497] [c000000fdca7bba0] [d00000001070ec6c] kvm_arch_vcpu_ioctl_run+0x5c/0x160 [kvm]
[  494.542504] [c000000fdca7bbe0] [d000000010703bf8] kvm_vcpu_ioctl+0x528/0x7a0 [kvm]
[  494.542506] [c000000fdca7bd40] [c0000000002c46dc] do_vfs_ioctl+0xcc/0x8e0
[  494.542509] [c000000fdca7bde0] [c0000000002c4f50] SyS_ioctl+0x60/0xc0
[  494.542512] [c000000fdca7be30] [c00000000000b760] system_call+0x38/0xfc
[  494.542514] INFO: task qemu-system-ppc:6870 blocked for more than 120 seconds.
[  494.542577]       Not tainted 4.10.0-rc8-00025-g0d75d3e #4
[  494.542615] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  494.542677] qemu-system-ppc D10688  6870   6473 0x00040000

Reverting this patch gets rid of the above hang. But I am running into segfault
with systemd in guest. It could be some other patches in my local tree.

Maybe we should hold merging this to 4.11 and wait for this to get more
testing ?

-aneesh