On Tue, Oct 15, 2013 at 10:53:10AM -0700, Hugh Dickins wrote: > I'm afraid Andrea's mail about concurrent madvises gives me far more > to think about than I have time for: seems to get into problems he > knows a lot about but I'm unfamiliar with. If this patch looks good > for now on its own, let's put it in; but no problem if you guys prefer > to wait for a fuller solution of more problems, we can ride with this > one internally for the moment. I'm very happy with the patch and I think it's a correct fix for the COW scenario which is deterministic so the looping makes a meaningful difference for it. If we wouldn't loop, part of the copied page wouldn't be zapped after the COW. The patch also solves the false positive for the other non deterministic scenario of two MADV_DONTNEED (one partial, one whole) plus a concurrent page fault. > And I should admit that the crash has occurred too rarely for us yet > to be able to judge whether this patch actually fixes it in practice. It is very rare indeed, and thanks to the BUG_ON it cannot lead to any user or kernel memory corruption, but it's a nuisance we need to fix. I only have the two stack traces in the two links I posted in the previous email and I also don't have the traces of the other CPU. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>