Tetsuo Handa wrote: > Michal Hocko wrote: > > On Sat 12-08-17 00:46:18, Tetsuo Handa wrote: > > > 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. > > > > Were you able to reproduce with other filesystems? > > Yes, I can reproduce this problem using both xfs and ext4 on 4.11.11-200.fc25.x86_64 > on Oracle VM VirtualBox on Windows. > > I believe that this is not old data from disk, for I can reproduce this problem > using newly attached /dev/sdb which has never written any data (other than data > written by mkfs.xfs and mkfs.ext4). > > /dev/sdb /tmp ext4 rw,seclabel,relatime,data=ordered 0 0 > > The garbage pattern (the last 4096 bytes) is identical for both xfs and ext4. I can reproduce this problem very easily using btrfs on 4.11.11-200.fc25.x86_64 on Oracle VM VirtualBox on Windows. /dev/sdb /tmp btrfs rw,seclabel,relatime,space_cache,subvolid=5,subvol=/ 0 0 The garbage pattern is identical for all xfs/ext4/btrfs. More complicated things a fs does, more likely to hit this problem? I tried ntfs but so far I am not able to reproduce this problem. -- 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>
