An mm_struct may be pinned by a file. An example is vhost-net device created by a qemu/kvm (see vhost_net_ioctl -> vhost_net_set_owner -> vhost_dev_set_owner). If such process gets OOM-killed, the reference to its mm_struct will only be released from exit_task_work -> ____fput -> __fput -> vhost_net_release -> vhost_dev_cleanup, which is called after exit_mmap, where TIF_MEMDIE is cleared. As a result, we can start selecting the next victim before giving the last one a chance to free its memory. In practice, this leads to killing several VMs along with the fattest one.
Signed-off-by: Vladimir Davydov <[email protected]> --- kernel/exit.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index fd90195667e1..cc50e12165f7 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -434,8 +434,6 @@ static void exit_mm(struct task_struct *tsk) task_unlock(tsk); mm_update_next_owner(mm); mmput(mm); - if (test_thread_flag(TIF_MEMDIE)) - exit_oom_victim(tsk); } static struct task_struct *find_alive_thread(struct task_struct *p) @@ -746,6 +744,8 @@ void do_exit(long code) disassociate_ctty(1); exit_task_namespaces(tsk); exit_task_work(tsk); + if (test_thread_flag(TIF_MEMDIE)) + exit_oom_victim(tsk); exit_thread(); /* -- 2.1.4
