MRP-1443 tests: lfs changelog_clear race test

Two or more lfs changelog_clear may race resulting in kernel
oops. This test forces the race to happen.

Change-Id: I0c4e72ebac47b0b5fac3becb0a45e70ec98b01c0
Signed-off-by: Vladimir Saveliev <vladimir_saveliev@xyratex.com>
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/1300
Tested-by: Jenkins
Reviewed-by: Alexander Zarochentsev <alexander_zarochentsev@xyratex.com>
Tested-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Reviewed-by: Andrew Perepechko <Andrew_Perepechko@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>
MRP-1443 llog: avoid llog cancel race

Concurrently running two or more lfs changelog_clear need to be
protected against races. llog_process_thread() used to read llogs
without taking into account that the llog being read may be destroyed
by another process. This patch serializes changelog cancellings using
llog_ctxt's mutex.

Signed-off-by: Vladimir Saveliev <vladimir_saveliev@xyratex.com>
Change-Id: I999fca1e909a44aaed1af63da651e629649c27c3
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/1301
Tested-by: Jenkins
Reviewed-by: Alexander Zarochentsev <alexander_zarochentsev@xyratex.com>
Reviewed-by: Andrew Perepechko <Andrew_Perepechko@xyratex.com>
Tested-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>