linux.git/drivers/md/dm-snap-persistent.c, branch v2.6.31

dm snapshot: fix on disk chunk size validation

2009-09-04T19:40:43+00:00

Fix some problems seen in the chunk size processing when activating a
pre-existing snapshot.

For a new snapshot, the chunk size can either be supplied by the creator
or a default value can be used.  For an existing snapshot, the
chunk size in the snapshot header on disk should always be used.

If someone attempts to load an existing snapshot and has the 'default
chunk size' option set, the kernel uses its default value even when it
is incorrect for the snapshot being loaded.  This patch ensures the
correct on-disk value is always used.

Secondly, when the code does use the chunk size stored on the disk it is
prudent to revalidate it, so the code can exit cleanly if it got
corrupted as happened in
https://bugzilla.redhat.com/show_bug.cgi?id=461506 .

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka 
Signed-off-by: Alasdair G Kergon

dm snapshot: fix header corruption race on invalidation

2009-09-04T19:40:39+00:00

If a persistent snapshot fills up, a race can corrupt the on-disk header
which causes a crash on any future attempt to activate the snapshot
(typically while booting).  This patch fixes the race.

When the snapshot overflows, __invalidate_snapshot is called, which calls
snapshot store method drop_snapshot. It goes to persistent_drop_snapshot that
calls write_header. write_header constructs the new header in the "area"
location.

Concurrently, an existing kcopyd job may finish, call copy_callback
and commit_exception method, that goes to persistent_commit_exception.
persistent_commit_exception doesn't do locking, relying on the fact that
callbacks are single-threaded, but it can race with snapshot invalidation and
overwrite the header that is just being written while the snapshot is being
invalidated.

The result of this race is a corrupted header being written that can
lead to a crash on further reactivation (if chunk_size is zero in the
corrupted header).

The fix is to use separate memory areas for each.

See the bug: https://bugzilla.redhat.com/show_bug.cgi?id=461506

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka 
Signed-off-by: Alasdair G Kergon

dm snapshot: refactor zero_disk_area to use chunk_io

2009-09-04T19:40:37+00:00

Refactor chunk_io to prepare for the fix in the following patch.

Pass an area pointer to chunk_io and simplify zero_disk_area to use
chunk_io.  No functional change.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka 
Signed-off-by: Alasdair G Kergon

dm snapshot: use barrier when writing exception store

2009-06-22T09:12:26+00:00

Send barrier requests when updating the exception area.

Exception area updates need to be ordered w.r.t. data writes, so that
the writes are not reordered in hardware disk cache.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Alasdair G Kergon

block: Do away with the notion of hardsect_size

2009-05-22T21:22:54+00:00

Until now we have had a 1:1 mapping between storage device physical
block size and the logical block sized used when addressing the device.
With SATA 4KB drives coming out that will no longer be the case.  The
sector size will be 4KB but the logical block size will remain
512-bytes.  Hence we need to distinguish between the physical block size
and the logical ditto.

This patch renames hardsect_size to logical_block_size.

Signed-off-by: Martin K. Petersen 
Signed-off-by: Jens Axboe

dm snapshot: persistent fix dtr cleanup

2009-04-02T18:55:35+00:00

The persistent exception store destructor does not properly
account for all conditions in which it can be called.  If it
is called after 'ctr' but before 'read_metadata' (e.g. if
something else in 'snapshot_ctr' fails) then it will attempt
to free areas of memory that haven't been allocated yet.

Signed-off-by: Jonathan Brassow 
Signed-off-by: Alasdair G Kergon

dm snapshot: move status to exception store

2009-04-02T18:55:35+00:00

Let the exception store types print out their status through
the new API, rather than having the snapshot code do it.

Adjust the buffer position to allow for the preceding DMEMIT in the
arguments to type->status().

Signed-off-by: Jonathan Brassow 
Signed-off-by: Alasdair G Kergon

dm snapshot: remove dm_snap header use

2009-04-02T18:55:33+00:00

Move useful functions out of dm-snap.h and stop using dm-snap.h.

Signed-off-by: Jonathan Brassow 
Signed-off-by: Alasdair G Kergon

dm exception store: move cow pointer

2009-04-02T18:55:33+00:00

Move COW device from snapshot to exception store.

Signed-off-by: Jonathan Brassow 
Signed-off-by: Alasdair G Kergon

dm exception store: move chunk_fields

2009-04-02T18:55:32+00:00

Move chunk fields from snapshot to exception store.

Signed-off-by: Jonathan Brassow 
Signed-off-by: Alasdair G Kergon