Messages in this thread | | | Date | Tue, 2 Feb 2016 14:21:44 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page() |
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On Mon 01-02-16 16:38:53, Kirill A. Shutemov wrote: > On Mon, Feb 01, 2016 at 03:24:46PM +0100, Michal Hocko wrote: > > On Mon 01-02-16 16:26:08, Kirill A. Shutemov wrote: > > > We don't care if there's a tail pages which is not on LRU. We are not > > > going to isolate them anyway. > > > > yes we are not going to isolate them but calling this function on a > > tail page is wrong in principle, no? PageLRU check is racy outside of > > lru_lock so what if we are racing here. I know, highly unlikely but not > > impossible. So I am not really sure this is an improvement. When would > > we hit this VM_BUG_ON and it wouldn't be a bug or at least suspicious > > usage? > > Yes, there is no point in calling isolate_lru_page() for tail pages, but > we do this anyway -- see the second patch.
yes, I have seen it and that is a bug as well AFAIU. So the VM_BUG_ON triggered for the real bug.
> And we need to validate all drivers, that they don't forget to set VM_IO > or make vma_migratable() return false in other way.
Yes, some drivers will do it incorrectly but this is VM_BUG_ON so it is usually disabled no?
> Alternative approach would be to downgrate the VM_BUG_ON_PAGE() to > WARN_ONCE_ON(). This way we would have chance to catch bad callers.
a ratelimitted WARN_ON would work as well. -- Michal Hocko SUSE Labs
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