Re: [PATCH v4] mm: per-thread vma caching

[Linus Torvalds]

On Sun, Mar 9, 2014 at 5:57 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> No, dup_task_struct() is obviously lockless. And the new child is not yet
> visible to for_each_process_thread().

Ok, then the siimple approach is to just do

    /* Did we miss an invalidate event? *
    if (mm->seqcount < tsk->seqcount)
        clear_vma_cache();

after making the new thread visible.

Then the "race" becomes one of "we cannot have 4 billion mmap/munmap
events in other threads while we're setting up a new thread", which I
think is fine.

               Linus
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