Re: [PATCH] oom: avoid killing init if it assume the oom killed thread'smm

From: Ming Liu
Date: Wed Sep 25 2013 - 01:50:05 EST

On 09/25/2013 10:34 AM, David Rientjes wrote:
On Mon, 23 Sep 2013, Ming Liu wrote:

After selecting a task to kill, the oom killer iterates all processes and
kills all other user threads that share the same mm_struct in different
thread groups.

But in some extreme cases, the selected task happens to be a vfork child
of init process sharing the same mm_struct with it, which causes kernel
panic on init getting killed. This panic is observed in a busybox shell
that busybox itself is init, with a kthread keeps consuming memories.

We shouldn't be selecting a process where mm == init_mm in the first
place, so this wouldn't fix the issue entirely.

But if we add a control point for "mm == init_mm" in the first place(ie. in oom_unkillable_task), that would forbid the processes sharing mm with init to be selected, is that reasonable? Actually my fix is just to protect init process to be killed for its vfork child being selected and I think it's the only place where there is the risk. If my understanding is wrong, pls correct me.

Ming Liu

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