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  1. 30 10月, 2008 2 次提交
    • M
      dm snapshot: wait for chunks in destructor · 879129d2
      由 Mikulas Patocka 提交于 
      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: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
      879129d2
    • M
      dm snapshot: fix register_snapshot deadlock · 60c856c8
      由 Mikulas Patocka 提交于 
      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: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
      60c856c8
  3. 22 10月, 2008 2 次提交
    • M
      dm snapshot: drop unused last_percent · f68d4f3d
      由 Mikulas Patocka 提交于 
      The last_percent field is unused - remove it.
(It dates from when events were triggered as each X% filled up.)
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
      f68d4f3d
    • M
      dm snapshot: fix primary_pe race · 7c5f78b9
      由 Mikulas Patocka 提交于 
      Fix a race condition with primary_pe ref_count handling.

put_pending_exception runs under dm_snapshot->lock, it does atomic_dec_and_test
on primary_pe->ref_count, and later does atomic_read primary_pe->ref_count.

__origin_write does atomic_dec_and_test on primary_pe->ref_count without holding
dm_snapshot->lock.

This opens the following race condition:
Assume two CPUs, CPU1 is executing put_pending_exception (and holding
dm_snapshot->lock). CPU2 is executing __origin_write in parallel.
primary_pe->ref_count == 2.

CPU1:
if (primary_pe && atomic_dec_and_test(&primary_pe->ref_count))
	origin_bios = bio_list_get(&primary_pe->origin_bios);
... decrements primary_pe->ref_count to 1. Doesn't load origin_bios

CPU2:
if (first && atomic_dec_and_test(&primary_pe->ref_count)) {
	flush_bios(bio_list_get(&primary_pe->origin_bios));
	free_pending_exception(primary_pe);
	/* If we got here, pe_queue is necessarily empty. */
	return r;
}
... decrements primary_pe->ref_count to 0, submits pending bios, frees
primary_pe.

CPU1:
if (!primary_pe || primary_pe != pe)
	free_pending_exception(pe);
... this has no effect.
if (primary_pe && !atomic_read(&primary_pe->ref_count))
	free_pending_exception(primary_pe);
... sees ref_count == 0 (written by CPU 2), does double free !!

This bug can happen only if someone is simultaneously writing to both the
origin and the snapshot.

If someone is writing only to the origin, __origin_write will submit kcopyd
request after it decrements primary_pe->ref_count (so it can't happen that the
finished copy races with primary_pe->ref_count decrementation).

If someone is writing only to the snapshot, __origin_write isn't invoked at all
and the race can't happen.

The race happens when someone writes to the snapshot --- this creates
pending_exception with primary_pe == NULL and starts copying. Then, someone
writes to the same chunk in the snapshot, and __origin_write races with
termination of already submitted request in pending_complete (that calls
put_pending_exception).

This race may be reason for bugs:
  http://bugzilla.kernel.org/show_bug.cgi?id=11636
  https://bugzilla.redhat.com/show_bug.cgi?id=465825

The patch fixes the code to make sure that:
1. If atomic_dec_and_test(&primary_pe->ref_count) returns false, the process
must no longer dereference primary_pe (because someone else may free it under
us).
2. If atomic_dec_and_test(&primary_pe->ref_count) returns true, the process
is responsible for freeing primary_pe.
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
Cc: stable@kernel.org
      7c5f78b9
  5. 21 7月, 2008 3 次提交
  7. 25 4月, 2008 5 次提交
  9. 29 3月, 2008 1 次提交
  11. 08 2月, 2008 2 次提交
  13. 20 10月, 2007 1 次提交
  15. 10 10月, 2007 1 次提交
  17. 13 7月, 2007 3 次提交
  19. 09 12月, 2006 3 次提交
  21. 08 12月, 2006 1 次提交
  23. 22 11月, 2006 1 次提交
  25. 03 10月, 2006 8 次提交
  27. 01 7月, 2006 1 次提交
  29. 27 6月, 2006 2 次提交
  31. 28 3月, 2006 4 次提交
    • A
      [PATCH] dm snapshot: fix kcopyd destructor · 138728dc
      由 Alasdair G Kergon 提交于 
      Before removing a snapshot, wait for the completion of any kcopyd jobs using
it.

Do this by maintaining a count (nr_jobs) of how many outstanding jobs each
kcopyd_client has.

The snapshot destructor first unregisters the snapshot so that no new kcopyd
jobs (created by writes to the origin) will reference that particular
snapshot.  kcopyd_client_destroy() is now run next to wait for the completion
of any outstanding jobs before the snapshot exception structures (that those
jobs reference) are freed.
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      138728dc
    • A
      [PATCH] dm: remove SECTOR_FORMAT · 4ee218cd
      由 Andrew Morton 提交于 
      We don't know what type sector_t has.  Sometimes it's unsigned long, sometimes
it's unsigned long long.  For example on ppc64 it's unsigned long with
CONFIG_LBD=n and on x86_64 it's unsigned long long with CONFIG_LBD=n.

The way to handle all of this is to always use unsigned long long and to
always typecast the sector_t when printing it.
Acked-by: NAlasdair G Kergon <agk@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      4ee218cd
    • A
      [PATCH] device-mapper snapshot: fix invalidation · 76df1c65
      由 Alasdair G Kergon 提交于 
      When a snapshot becomes invalid, s->valid is set to 0.  In this state, a
snapshot can no longer be accessed.

When s->lock is acquired, before doing anything else, s->valid must be checked
to ensure the snapshot remains valid.

This patch eliminates some races (that may cause panics) by adding some
missing checks.  At the same time, some unnecessary levels of indentation are
removed and snapshot invalidation is moved into a single function that always
generates a device-mapper event.
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      76df1c65
    • A
      [PATCH] device-mapper snapshot: replace sibling list · b4b610f6
      由 Alasdair G Kergon 提交于 
      The siblings "list" is used unsafely at the moment.

Firstly, only the element on the list being changed gets locked (via the
snapshot lock), not the next and previous elements which have pointers that
are also being changed.

Secondly, if you have two or more snapshots and write to the same chunk a
second time before every snapshot has finished making its private copy of the
data, if you're unlucky, _origin_write() could attempt its list_merge() and
dereference a 'last' pointer to a pending_exception structure that has just
been freed.

Analysis reveals that the list is actually only there for reference counting.
If 5 pending_exceptions are needed in origin_write, then the 5 are joined
together into a 5-element list - without a separate list head because there's
nowhere suitable to store it.  As the pending_exceptions complete, they are
removed from the list one-by-one and any contents of origin_bios get moved
across to one of the remaining pending_exceptions on the list.  Whichever one
is last is detected because list_empty() is then true and the origin_bios get
submitted.

The fix proposed here uses an alternative reference counting mechanism by
choosing one of the pending_exceptions as primary and maintaining an atomic
counter there.
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      b4b610f6