Re: [PATCH] exit: clear TIF_MEMDIE after exit_task_work
From: Michal Hocko <mhocko@kernel.org>
Date: 2016-02-29 18:21:36
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On Mon 29-02-16 20:02:09, Vladimir Davydov wrote:
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.
I am wondering why our PF_EXITING protection hasn't fired up. This is not done in the mmotm tree but I guess you have seen the issue with the linus tree, right? Do you have a log with oom reports available? To be honest I do not feel very comfortable about moving the exit_oom_victim even further down in do_exit path behind even less clear locking or other dependencies. Let's see if we can do any better for this particular case.
quoted hunk ↗ jump to hunk
Signed-off-by: Vladimir Davydov <redacted> --- 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
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