Messages in this thread | | | From | (Eric W. Biederman) | Date | Thu, 03 May 2018 09:39:03 -0500 | Subject | Re: [PATCH] memcg: Replace mm->owner with mm->memcg |
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Oleg Nesterov <oleg@redhat.com> writes:
> On 05/02, Eric W. Biederman wrote: >> >> +static void mem_cgroup_fork(struct task_struct *tsk) >> +{ >> + struct cgroup_subsys_state *css; >> + >> + rcu_read_lock(); >> + css = task_css(tsk, memory_cgrp_id); >> + if (css && css_tryget(css)) >> + task_update_memcg(tsk, mem_cgroup_from_css(css)); >> + rcu_read_unlock(); >> +} > > Why do we need it? > > The child's mm->memcg was already initialized by mm_init_memcg() and we can't > race with migrate until cgroup_threadgroup_change_end() ?
I admit I missed the cgroup_threadgroup_change_begin cgroup_threadgroup_change_end pair in fs fork. In this case it doesn't matter because mm_init_memcg is called from:
copy_mm dup_mm mm_init
And copy_mm is called before we call cgroup_threadgroup_change_begin. So the race remains.
We could move move cgroup_threadgroup_change_begin earlier, to remove the need for mem_cgroup_fork. But I have not analyzed that.
Eric
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