Zach Brown 95d8f4bf20 scoutfs: only allow recursive blocked hold ...

fsx-mpi spins creating contention between ex holders of locks between
nodes.  It was tripping assertions in item invalidation as it tried to
invalidate dirty items.  Tracing showed that we were allowing holders of
locks while we were invalidating.  Our invalidation function would
commit the current transaction, another task would hold the lock and
dirty an item, and then invalidation would continue on and try to
invalidate the dirty item.  The invalidation code has always assumed
that it's not running concurrently with item dirtying.

The recursive locking change allowed acquireing blocked locks if the
recursive flag was set.  It'd then check holders after calling
downconvert_worker (invalidation for us) and retry the downconvert if a
holder appeared.  That it allowed recursive holders regardless of who
was alredy holding the lock is what let holders arrive once downconvert
started on the blocked lock.  Not only did this create our problem with
invalidation, it also could leave items behind if the holder dirtied an
item and dropped the lock between invalidation and before downconvert
checked the holders again.

The fix is to only allow recursive holders on blocked locks that already
have holders.  This ensures that holders will never increase past zero
on blocked locks.  Once the downconvert sees the holders drain it will
call invalidation which won't have racing dirtiers.  We can remove the
holder check after invalidation entirely.

With this fixed fsx-mpi no longer tries to invalidate dirty items as it
bounces locks back and forth.

Signed-off-by: Zach Brown <zab@versity.com>

2017-10-26 14:47:59 -07:00

kmod

scoutfs: only allow recursive blocked hold

2017-10-26 14:47:59 -07:00

Description

No description provided

8 MiB

Languages

C 87%

Shell 9.3%

Roff 2.5%

TeX 0.8%

Makefile 0.4%