• Tejun Heo's avatar
    cgroup: statically initialize init_css_set->dfl_cgrp · 38683148
    Tejun Heo authored
    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-g041cd640 #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: 041cd640 ("cgroup: Implement cgroup2 basic CPU usage accounting")
    Reported-by: default avatar“kbuild-all@01.org” <kbuild-all@01.org>
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    38683148
cgroup.c 152 KB