linux-kernel - Re: mm, we use rcu access task_struct in mm_match_cgroup(), but not use rcu free in free_task

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Date:   Wed, 24 May 2017 12:40:03 +0800
From:   Xishi Qiu <qiuxishi@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Hugh Dickins <hughd@...gle.com>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        Minchan Kim <minchan@...nel.org>,
        "wencongyang (A)" <wencongyang2@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Dmitry Vyukov" <dvyukov@...gle.com>,
        zhong jiang <zhongjiang@...wei.com>
CC:     Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: mm, we use rcu access task_struct in mm_match_cgroup(), but not
 use rcu free in free_task_struct()

On 2017/5/24 9:40, Xishi Qiu wrote:

> Hi, I find we use rcu access task_struct in mm_match_cgroup(), but not use
> rcu free in free_task_struct(), is it right?
> 
> Here is the backtrace.
> 
> PID: 2133   TASK: ffff881fe3353300  CPU: 2   COMMAND: "CPU 15/KVM"
>  #0 [ffff881fe276b528] machine_kexec at ffffffff8105280b
>  #1 [ffff881fe276b588] crash_kexec at ffffffff810f5072
>  #2 [ffff881fe276b658] panic at ffffffff8163e23b
>  #3 [ffff881fe276b6d8] oops_end at ffffffff8164d61b
>  #4 [ffff881fe276b700] die at ffffffff8101872b
>  #5 [ffff881fe276b730] do_general_protection at ffffffff8164cefe
>  #6 [ffff881fe276b760] general_protection at ffffffff8164c7a8
>     [exception RIP: mem_cgroup_from_task+22]
>     RIP: ffffffff811db536  RSP: ffff881fe276b810  RFLAGS: 00010286
>     RAX: 6b6b6b6b6b6b6b6b  RBX: ffffea007f988880  RCX: 0000000000020000
>     RDX: 00000007fa607d67  RSI: 00000007fa607d67  RDI: ffff880fe36d72c0
>     RBP: ffff881fe276b880   R8: 00000007fa607600   R9: a801fd67b3000000
>     R10: 57fdec98cc59ecc0  R11: ffff880fe2e8dbd0  R12: ffffc9001cb74000
>     R13: ffff881fdb8cfda0  R14: ffff881fe2581570  R15: 00000007fa607d67
>     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0000
>  #7 [ffff881fe276b810] page_referenced at ffffffff811a6b8a
>  #8 [ffff881fe276b888] shrink_page_list at ffffffff81180994
>  #9 [ffff881fe276b9c0] shrink_inactive_list at ffffffff8118166a
> #10 [ffff881fe276ba88] shrink_lruvec at ffffffff81182135
> #11 [ffff881fe276bb88] shrink_zone at ffffffff81182596
> #12 [ffff881fe276bbe0] do_try_to_free_pages at ffffffff81182a90
> #13 [ffff881fe276bc58] try_to_free_mem_cgroup_pages at ffffffff81182fea
> #14 [ffff881fe276bcf0] mem_cgroup_reclaim at ffffffff811dd8de
> #15 [ffff881fe276bd30] __mem_cgroup_try_charge at ffffffff811ddd9c
> #16 [ffff881fe276bdf0] __mem_cgroup_try_charge_swapin at ffffffff811df62b
> #17 [ffff881fe276be28] mem_cgroup_try_charge_swapin at ffffffff811e0537
> #18 [ffff881fe276be38] handle_mm_fault at ffffffff8119abdd
> #19 [ffff881fe276bec8] __do_page_fault at ffffffff816502d6
> #20 [ffff881fe276bf28] do_page_fault at ffffffff81650603
> #21 [ffff881fe276bf50] page_fault at ffffffff8164c808
>     RIP: 00007fdaba456500  RSP: 00007fdaaba6c978  RFLAGS: 00010246
>     RAX: ffffffffffffffff  RBX: 0000000000000000  RCX: fffffffffffffbd0
>     RDX: 0000000000000000  RSI: 000000000000ae80  RDI: 000000000000002c
>     RBP: 00007fdaaba6c9f0   R8: 0000000000840c70   R9: 00000000000000be
>     R10: 000000007fffffff  R11: 0000000000000246  R12: 0000000003622010
>     R13: 000000000000ae80  R14: 00000000008274e0  R15: 0000000003622010
>     ORIG_RAX: ffffffffffffffff  CS: 0033  SS: 002b
> 
> 
> .
>