On Thu, 2014-03-13 at 16:32 +0100, Oleg Nesterov wrote: > On 03/13, Oleg Nesterov wrote: > > > > Yes. But it seems that use_mm() and unuse_mm() should invalidate vmacache > > too. > > > > Suppose that a kernel thread T does, say, > > > > use_mm(foreign_mm); > > get_user(...); > > unuse_mm(); > > > > This can trigger a fault and populate T->vmacache[]. If this code is called > > again vmacache_find() can use the stale entries. > > > > Or, assuming that only a kernel thread can do use_mm(), we can change > > vmacache_valid() to also check !PF_KTHREAD. > > Yes, I think we should check PF_KTHREAD, because > > > Hmm. Another problem is that use_mm() doesn't take ->mmap_sem and thus > > it can race with vmacache_flush_all()... > > this also closes this race. use_mm() users should not use vmacache at all. > > > Finally. Shouldn't vmacache_update() check current->mm == mm as well? > > What if access_remote_vm/get_user_pages trigger find_vma() ??? Unless > > I missed something this is not theoretical at all and can lead to the > > corrupted vmacache, no? > > Looks like a real problem or I am totally confused. I think we need > something like below (uncompiled).
Thanks for looking into this Oleg. I was actually chasing a bug triggered by trinity where we have a stale cache and vmacache_find() is returning a bogus vma structure even when vma->vm_mm != mm: https://lkml.org/lkml/2014/3/9/201 https://lkml.org/lkml/2014/3/11/563 So it just might be a real problem. -- 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/
