On Wed 06-11-19 14:51:30, Roman Gushchin wrote: > 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 > ? unix_stream_sendmsg+0x37d/0x3b0 > get_signal+0x132/0x7c0 > do_signal+0x36/0x640 > ? recalc_sigpending+0x17/0x50 > 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. Hmm, how can we have a task in an offline memcg? I thought that any existing task will prevent cgroup removal from proceeding. Is this some sort of race where the task managed to disassociate from the cgroup while there is still a binding to a memcg existing? What am I missing? -- Michal Hocko SUSE Labs
