Michal Hocko wrote: > On Fri 11-08-17 16:54:36, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > On Fri 11-08-17 11:28:52, Tetsuo Handa wrote: > > > > Will you explain the mechanism why random values are written instead of zeros > > > > so that this patch can actually fix the race problem? > > > > > > I am not sure what you mean here. Were you able to see a write with an > > > unexpected content? > > > > Yes. See http://lkml.kernel.org/r/201708072228.FAJ09347.tOOVOFFQJSHMFL@xxxxxxxxxxxxxxxxxxx . > > Ahh, I've missed that random part of your output. That is really strange > because AFAICS the oom reaper shouldn't really interact here. We are > only unmapping anonymous memory and even if a refault slips through we > should always get zeros. > > Your test case doesn't mmap MAP_PRIVATE of a file so we shouldn't even > get any uninitialized data from a file by missing CoWed content. The > only possible explanations would be that a page fault returned a > non-zero data which would be a bug on its own or that a file write > extend the file without actually writing to it which smells like a fs > bug to me. As I wrote at http://lkml.kernel.org/r/201708112053.FIG52141.tHJSOQFLOFMFOV@xxxxxxxxxxxxxxxxxxx , I don't think it is a fs bug. > > Anyway I wasn't able to reproduce this and I was running your usecase > in the loop for quite some time (with xfs storage). How reproducible > is this? If you can reproduce easily can you simply comment out > unmap_page_range in __oom_reap_task_mm and see if that makes any change > just to be sure that the oom reaper can be ruled out? Frequency of writing not-zero values is lower than frequency of writing zero values. But if I comment out unmap_page_range() in __oom_reap_task_mm(), I can't even reproduce writing zero values. As far as I tested, writing not-zero values occurs only if the OOM reaper is involved. -- 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>
