On Tue, Nov 10, 2015 at 2:51 PM, Jan Kara wrote: > Another version of my ext4 fixes. Since previous version I have fixed DAX block > mapping to really avoid races for parallel page faults so that the test program > by Brian passes. Note that you'll see ext4/001 failures - xfstests updates were Thanks for the updated patches! > submitted. Also note that testing with 1 KB blocksize on ramdisk is broken > since brd has buggy discard implementation - Jens has a fix queued. > > Change since v3: > * Fixed ext4_dax_mmap_get_block() to not return buffer_new buffer and thus > avoid racy zeroing in generic dax code > * Fixed ext4_map_blocks() to zeroout blocks before inserting entry into > extent status tree to avoid racy lookups of blocks. > > Changes since v2: > * Fixed collaps range to truncate pagecache properly with blocksize < pagesize > * Fixed assertion in ext4_get_blocks_overwrite > > Patch set description > > 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). Is this still a problem for this version of the patch set? Thanks! Brian > 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. -- 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
