linux-stable.git/drivers/md/dm-snap.c, branch linux-2.6.29.y

dm snapshot: avoid having two exceptions for the same chunk

2009-04-27T17:36:57+00:00

upstream commit: 35bf659b008e83e725dcd30f542e38461dbb867c

We need to check if the exception was completed after dropping the lock.

After regaining the lock, __find_pending_exception checks if the exception
was already placed into &s->pending hash.

But we don't check if the exception was already completed and placed into
&s->complete hash. If the process waiting in alloc_pending_exception was
delayed at this point because of a scheduling latency and the exception
was meanwhile completed, we'd miss that and allocate another pending
exception for already completed chunk.

It would lead to a situation where two records for the same chunk exist
and potential data corruption because multiple snapshot I/Os to the
affected chunk could be redirected to different locations in the
snapshot.

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

dm snapshot: avoid dropping lock in __find_pending_exception

2009-04-27T17:36:57+00:00

upstream commit: c66213921c816f6b1b16a84911618ba9a363b134

It is uncommon and bug-prone to drop a lock in a function that is called with
the lock held, so this is moved to the caller.

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

dm snapshot: refactor __find_pending_exception

2009-04-27T17:36:56+00:00

upstream commit: 2913808eb56a6445a7b277eb8d17651c8defb035

Move looking-up of a pending exception from __find_pending_exception to another
function.

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

dm snapshot: extend exception store functions

2009-01-06T03:05:19+00:00

Supply dm_add_exception as a callback to the read_metadata function.
Add a status function ready for a later patch and name the functions
consistently.

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

dm snapshot: split out exception store implementations

2009-01-06T03:05:17+00:00

Move the existing snapshot exception store implementations out into
separate files.  Later patches will place these behind a new
interface in preparation for alternative implementations.

Signed-off-by: Alasdair G Kergon

dm snapshot: separate out exception store interface

2009-01-06T03:05:15+00:00

Pull structures that bridge the gap between snapshot and
exception store out of dm-snap.h and put them in a new
.h file - dm-exception-store.h.  This file will define the
API for new exception stores.

Ultimately, dm-snap.h is unnecessary, since only dm-snap.c
should be using it.

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

dm: consolidate target deregistration error handling

2009-01-06T03:04:58+00:00

Change dm_unregister_target to return void and use BUG() for error
reporting.

dm_unregister_target can only fail because of programming bug in the
target driver. It can't fail because of user's behavior or disk errors.

This patch changes unregister_target to return void and use BUG if
someone tries to unregister non-registered target or unregister target
that is in use.

This patch removes code duplication (testing of error codes in all dm
targets) and reports bugs in just one place, in dm_unregister_target. In
some target drivers, these return codes were ignored, which could lead
to a situation where bugs could be missed.

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

dm snapshot: change yield to msleep

2009-01-06T03:04:54+00:00

Change yield() to msleep(1). If the thread had realtime priority,
yield() doesn't really yield, so the yielding process would loop
indefinitely and cause machine lockup.

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

dm snapshot: wait for chunks in destructor

2008-10-30T13:33:16+00:00

If there are several snapshots sharing an origin and one is removed
while the origin is being written to, the snapshot's mempool may get
deleted while elements are still referenced.

Prior to dm-snapshot-use-per-device-mempools.patch the pending
exceptions may still have been referenced after the snapshot was
destroyed, but this was not a problem because the shared mempool
was still there.

This patch fixes the problem by tracking the number of mempool elements
in use.

The scenario:
- You have an origin and two snapshots 1 and 2.
- Someone writes to the origin.
- It creates two exceptions in the snapshots, snapshot 1 will be primary
exception, snapshot 2's pending_exception->primary_pe will point to the
exception in snapshot 1.
- The exceptions are being relocated, relocation of exception 1 finishes
(but it's pending_exception is still allocated, because it is referenced
by an exception from snapshot 2)
- The user lvremoves snapshot 1 --- it calls just suspend (does nothing)
and destructor. md->pending is zero (there is no I/O submitted to the
snapshot by md layer), so it won't help us.
- The destructor waits for kcopyd jobs to finish on snapshot 1 --- but
there are none.
- The destructor on snapshot 1 cleans up everything.
- The relocation of exception on snapshot 2 finishes, it drops reference
on primary_pe. This frees its primary_pe pointer. Primary_pe points to
pending exception created for snapshot 1. So it frees memory into
non-existing mempool.

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

dm snapshot: fix register_snapshot deadlock

2008-10-30T13:33:12+00:00

register_snapshot() performs a GFP_KERNEL allocation while holding
_origins_lock for write, but that could write out dirty pages onto a
device that attempts to acquire _origins_lock for read, resulting in
deadlock.

So move the allocation up before taking the lock.

This path is not performance-critical, so it doesn't matter that we
allocate memory and free it if we find that we won't need it.

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