On Fri, Nov 06, 2015 at 05:57:04PM +0000, Boylston, Brian wrote: > Hi, > > I've written a test tool (included below) that exercises page faults on > hole-y portions of an mmapped file. The file is created, sized using > various methods, mmapped, and then two threads race to write a marker to > different offsets within each mapped page. Once the threads have > finished marking each page, the pages are checked for the presence of > the markers. > > With vanilla 4.2 and 4.3 kernels, this test easily exposes corruption on > pmem-backed, DAX-mounted xfs and ext4 file systems. 4.2/4.3 kernels do not have a fix for this race problem in them, so it's no surprise that they fail the test. The fixes for this problem in XFS are currently in the for-next branch, and will be merged into 4.4 during the merge window. And FWIW, with XFS on a ramdisk on a 4.3+for-next branch kernel, this test passes just fine: $ ./dax-hole-test -f /mnt/scratch/holetest 1000 holetest r0 INFO: zero-filled test... INFO: sz = 3e800000, npages = 256000 INFO: vastart = 00007fc5a90bd000 INFO: thread 0 is 7fc5a90bc700 INFO: thread 1 is 7fc5a88bb700 INFO: 0 error(s) detected INFO: posix_fallocate test... INFO: sz = 3e800000, npages = 256000 INFO: vastart = 00007fc5a90bd000 INFO: thread 0 is 7fc5a88bb700 INFO: thread 1 is 7fc5a90bc700 INFO: 0 error(s) detected INFO: fallocate test... INFO: sz = 3e800000, npages = 256000 INFO: vastart = 00007fc5a90bd000 INFO: thread 0 is 7fc5a90bc700 INFO: thread 1 is 7fc5a88bb700 INFO: 0 error(s) detected INFO: ftruncate test... INFO: sz = 3e800000, npages = 256000 INFO: vastart = 00007fc5a90bd000 INFO: thread 0 is 7fc5a88bb700 INFO: thread 1 is 7fc5a90bc700 INFO: 0 error(s) detected That tends to indicate a bug in the ext4 patchset, not that the method we've taken to solve the problem is fundamentally wrong. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
