On Thu 22-10-15 12:09:10, Ross Zwisler wrote: > On Thu, Oct 22, 2015 at 10:15:52AM +0200, Jan Kara wrote: > > Hello, > > > > This series fixes a long standing problem of racing punch hole and page fault > > resulting in possible filesystem corruption or stale data exposure. We fix the > > problem by using a new inode-private rw_semaphore i_mmap_sem to synchronize > > page faults with truncate and punch hole operations. > > > > When having this exclusion, the only remaining problem with DAX implementation > > are races between two page faults zeroing out same block concurrently (where > > the data written after the first fault finishes are possibly overwritten by > > the second fault still doing zeroing). > > > > Patch 1 introduces i_mmap_sem lock in ext4 inode and uses it to properly > > serialize extent manipulation operations and page faults. > > > > Patch 2 is mostly a preparatory cleanup patch which also avoids double lock / > > unlock in unlocked DIO protections (currently harmless but nasty surprise). > > > > Patches 3-4 fix further races of extent manipulation functions (such as zero > > range, collapse range, insert range) with buffered IO, page writeback > > > > Patch 5 documents locking order of ext4 filesystem locks. > > > > Patch 6 removes locking abuse of i_data_sem from the get_blocks() path when > > dioread_nolock is enabled since it is not needed anymore. > > > > Patches 7-9 implement allocation of pre-zeroed blocks in ext4_map_blocks() > > callback and use such blocks for allocations from DAX page faults. > > > > The patches survived xfstests run both in dax and non-dax mode. > > > > Honza > > In my setup generic/081 passes, but causes all sorts of errors reported in > syslog. I think these errors are a normal part of the test because they happen > in the non-DAX case as well, but in the DAX case I think we end up in a bad > state. After this, all other tests fail. Thanks for report! I was using ramdisk for testing and test generic/081 got skipped because the device doesn't have "sane flush". I'll retest with pmem and debug what's going on. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- 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
