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.
Here is a run of generic/081 and generic/082, where generic/082 dies as a
bystander of the bad state left by generic/081:
# ./check generic/081 generic/082
FSTYP -- ext4
PLATFORM -- Linux/x86_64 lorwyn 4.3.0-rc6_ext4_dax_v2+
MKFS_OPTIONS -- /dev/pmem0p2
MOUNT_OPTIONS -- -o dax -o context=system_u:object_r:nfs_t:s0 /dev/pmem0p2 /mnt/xfstests_scratch
generic/081 2s ... 1s
generic/082 0s ... [failed, exit status 1] - output mismatch (see /root/xfstests/results//generic/082.out.bad)
--- tests/generic/082.out 2015-10-02 10:20:40.816712128 -0600
+++ /root/xfstests/results//generic/082.out.bad 2015-10-22 12:07:06.009024134 -0600
@@ -1,3 +1,9 @@
QA output created by 082
-group quota on SCRATCH_MNT (SCRATCH_DEV) is on
-user quota on SCRATCH_MNT (SCRATCH_DEV) is on
+mount: /dev/pmem0p2 is already mounted or /mnt/xfstests_scratch busy
+quotaon: Mountpoint (or device) /mnt/xfstests_scratch not found or has no quota enabled.
+mount: /mnt/xfstests_scratch not mounted or bad option
+
...
(Run 'diff -u tests/generic/082.out /root/xfstests/results//generic/082.out.bad' to see the entire diff)
Ran: generic/081 generic/082
Failures: generic/082
Failed 1 of 2 tests
When run by itself on a clean system with DAX generic/082 passes repeatedly.
After you get into this bad state, all other tests fail to run:
# ./check generic/082
FSTYP -- ext4
PLATFORM -- Linux/x86_64 lorwyn 4.3.0-rc6_ext4_dax_v2+
MKFS_OPTIONS -- /dev/pmem0p2
MOUNT_OPTIONS -- -o dax -o context=system_u:object_r:nfs_t:s0 /dev/pmem0p2 /mnt/xfstests_scratch
our local _scratch_mkfs routine ...
mke2fs 1.42.12 (29-Aug-2014)
/dev/pmem0p2 is apparently in use by the system; will not make a filesystem here!
check: failed to mkfs $SCRATCH_DEV using specified options
Passed all 0 tests
--
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
