On 03/09, Linus Torvalds wrote: > > On Sun, Mar 9, 2014 at 5:57 AM, Oleg Nesterov <o...@redhat.com> 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",
But it's not the "while we're setting up a new thread", it is "since vmacache_valid() was called list time". And the cloning task can just sleep(A_LOT) and then do CLONE_VM. Of course, of course, this race is pute theoretical anyway. But imho makes sense to fix anyway, and the natural/trivial approach is just to move vmacache_flush(tsk) from dup_mm() to copy_mm(), right after the "if (!oldmm)" check. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
