lkml.org 
[lkml]   [2017]   [Sep]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH cgroup/for-4.15] cgroup: statically initialize init_css_set->dfl_cgrp
    Hello,

    A follow-up patch to fix sporadic oops during boot which is caused by
    trying dereference the default cgroup from accounting code before
    cgroup is initialized.

    Applied to cgroup/for-4.15.

    Thanks.
    ------ 8< ------
    From 38683148828165ea0b66ace93a9fedc2d3281e27 Mon Sep 17 00:00:00 2001
    From: Tejun Heo <tj@kernel.org>
    Date: Mon, 25 Sep 2017 13:50:20 -0700
    MIME-Version: 1.0
    Content-Type: text/plain; charset=UTF-8
    Content-Transfer-Encoding: 8bit

    Like other csets, init_css_set's dfl_cgrp is initialized when the cset
    gets linked. init_css_set gets linked in cgroup_init(). This has
    been fine till now but the recently added basic CPU usage accounting
    may end up accessing dfl_cgrp of init before cgroup_init() leading to
    the following oops.

    SELinux: Initializing.
    BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0
    IP: account_system_index_time+0x60/0x90
    PGD 0 P4D 0
    Oops: 0000 [#1] SMP
    Modules linked in:
    CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc2-00003-g041cd64 #10
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
    +1.9.3-20161025_171302-gandalf 04/01/2014
    task: ffffffff81e10480 task.stack: ffffffff81e00000
    RIP: 0010:account_system_index_time+0x60/0x90
    RSP: 0000:ffff880011e03cb8 EFLAGS: 00010002
    RAX: ffffffff81ef8800 RBX: ffffffff81e10480 RCX: 0000000000000003
    RDX: 0000000000000000 RSI: 00000000000f4240 RDI: 0000000000000000
    RBP: ffff880011e03cc0 R08: 0000000000010000 R09: 0000000000000000
    R10: 0000000000000020 R11: 0000003b9aca0000 R12: 000000000001c100
    R13: 0000000000000000 R14: ffffffff81e10480 R15: ffffffff81e03cd8
    FS: 0000000000000000(0000) GS:ffff880011e00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00000000000000b0 CR3: 0000000001e09000 CR4: 00000000000006b0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
    <IRQ>
    account_system_time+0x45/0x60
    account_process_tick+0x5a/0x140
    update_process_times+0x22/0x60
    tick_periodic+0x2b/0x90
    tick_handle_periodic+0x25/0x70
    timer_interrupt+0x15/0x20
    __handle_irq_event_percpu+0x7e/0x1b0
    handle_irq_event_percpu+0x23/0x60
    handle_irq_event+0x42/0x70
    handle_level_irq+0x83/0x100
    handle_irq+0x6f/0x110
    do_IRQ+0x46/0xd0
    common_interrupt+0x9d/0x9d

    Fix it by statically initializing init_css_set.dfl_cgrp so that init's
    default cgroup is accessible from the get-go.

    Fixes: 041cd640b2f3 ("cgroup: Implement cgroup2 basic CPU usage accounting")
    Reported-by: “kbuild-all@01.org” <kbuild-all@01.org>
    Signed-off-by: Tejun Heo <tj@kernel.org>
    ---
    kernel/cgroup/cgroup.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
    index d036625..7975b20 100644
    --- a/kernel/cgroup/cgroup.c
    +++ b/kernel/cgroup/cgroup.c
    @@ -649,6 +649,14 @@ struct css_set init_css_set = {
    .cgrp_links = LIST_HEAD_INIT(init_css_set.cgrp_links),
    .mg_preload_node = LIST_HEAD_INIT(init_css_set.mg_preload_node),
    .mg_node = LIST_HEAD_INIT(init_css_set.mg_node),
    +
    + /*
    + * The following field is re-initialized when this cset gets linked
    + * in cgroup_init(). However, let's initialize the field
    + * statically too so that the default cgroup can be accessed safely
    + * early during boot.
    + */
    + .dfl_cgrp = &cgrp_dfl_root.cgrp,
    };

    static int css_set_count = 1; /* 1 for init_css_set */
    --
    2.9.5
    \
     
     \ /
      Last update: 2017-09-25 23:11    [W:7.497 / U:0.080 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site