LU-15535 llite: deadlock on lli_lsm_sem

LU-15535 llite: deadlock on lli_lsm_sem

it may happen that one process is doing lookup, and after reply while
holding the LDLM lock is trying to update LSM/default LSM under the
write lli_lsm_sem for a dir.

another process has taken the read lli_lsm_sem (taken for all the MD
ops in ll_prep_md_op_data()) and is waiting for a conflicting PW LDLM
lock on server for its modification for this dir.

it may happen on restriping with LSM, on changing the default LSM, but
even more often way is racer run even without striped dirs:
- racer does LFS mkdir -i $i <subdir> per each MDS, what creates a default
  LSM on these subdirs inherited endlessly - to keep the MDS index;
- racer also does mkdir -p <path>, in which case we do:
	ll_new_node - create a parent dir, no RMF_DEFAULT_MDT_MD in reply
	ll_lookup parent it=open - no RMF_DEFAULT_MDT_MD in reply
	ll_new_node - create a child
the default LSM is inherited on the parent creation, however as those RPCs
do not have lookup LDLM lock and no data - the default layout is not set
for the parent in inode at the time of a child creation. thus a parallel
lookup which gets the LSM deadlocks with this ll_new_node().

at the same time, similar to CLIO, we do not need to hold a sem nor an
LDLM lock over the whole operation to avoid LSM modification on server,
we just need to take an uptodate LSM (this is a subject for LU-16320)
and to guarantee this op will be working on the client on this LSM for
the whole operation.

the solution is to let MD ops to work on a copy of LSM therefore letting
others to modify LSM attached to inode in parallel if needed.

Lustre-change: https://review.whamcloud.com/50489
Lustre-commit: 3ebc8e0528e34a11ffeff1e6be347de18b248069

HPE-bug-id: LUS-10725
Signed-off-by: Vitaly Fertman <vitaly.fertman@hpe.com>
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I3137300b5bcce2e890994ce8751cdf7fce2f3f54
Reviewed-on: https://es-gerrit.hpc.amslabs.hpecorp.net/161525
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51828
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>