The bug was caused by race between truncate & fsync.
osc_extent_wait() doesn't takes into account oe_trunc_pending
during setting oe_urgent. The race arises after
osc_object_unlock().
osc_extent_wait() should ignore extents with oe_trunc_pending
while waiting for OES_INV. osc_cache_truncate_end() will set
oe_urgent and call osc_io_unplug_async()