• R
    mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() · bb1bc2d8
    Roman Gushchin 提交于
    commit 00d484f354d85845991b40141d40ba9e5eb60faf upstream.
    
    We've encountered a rcu stall in get_mem_cgroup_from_mm():
    
      rcu: INFO: rcu_sched self-detected stall on CPU
      rcu: 33-....: (21000 ticks this GP) idle=6c6/1/0x4000000000000002 softirq=35441/35441 fqs=5017
      (t=21031 jiffies g=324821 q=95837) NMI backtrace for cpu 33
      <...>
      RIP: 0010:get_mem_cgroup_from_mm+0x2f/0x90
      <...>
       __memcg_kmem_charge+0x55/0x140
       __alloc_pages_nodemask+0x267/0x320
       pipe_write+0x1ad/0x400
       new_sync_write+0x127/0x1c0
       __kernel_write+0x4f/0xf0
       dump_emit+0x91/0xc0
       writenote+0xa0/0xc0
       elf_core_dump+0x11af/0x1430
       do_coredump+0xc65/0xee0
       get_signal+0x132/0x7c0
       do_signal+0x36/0x640
       exit_to_usermode_loop+0x61/0xd0
       do_syscall_64+0xd4/0x100
       entry_SYSCALL_64_after_hwframe+0x44/0xa9
    
    The problem is caused by an exiting task which is associated with an
    offline memcg.  We're iterating over and over in the do {} while
    (!css_tryget_online()) loop, but obviously the memcg won't become online
    and the exiting task won't be migrated to a live memcg.
    
    Let's fix it by switching from css_tryget_online() to css_tryget().
    
    As css_tryget_online() cannot guarantee that the memcg won't go offline,
    the check is usually useless, except some rare cases when for example it
    determines if something should be presented to a user.
    
    A similar problem is described by commit 18fa84a2db0e ("cgroup: Use
    css_tryget() instead of css_tryget_online() in task_get_css()").
    
    Johannes:
    
    : The bug aside, it doesn't matter whether the cgroup is online for the
    : callers.  It used to matter when offlining needed to evacuate all charges
    : from the memcg, and so needed to prevent new ones from showing up, but we
    : don't care now.
    
    Link: http://lkml.kernel.org/r/20191106225131.3543616-1-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
    Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
    Acked-by: NTejun Heo <tj@kernel.org>
    Reviewed-by: NShakeel Butt <shakeeb@google.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Michal Koutn <mkoutny@suse.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    bb1bc2d8
memcontrol.c 172.1 KB