It was missed kio/pcs module has warning on out of mutex execution
of fallocate request. It is not a bug per se, yet the situation
is dubious. The rationale was that logically fallocate(zerorange) is
_not_ different of aio direct write of zeros to the same area,
and that write used to be executed o
FMODE_NOWAIT is new kernel API added quite a while ago, but activated
in the latest rhel updates. Earlier kernels had a bug,
fses without associated bdev (like fuse or any other virtual
file system) enforced this flag at top level. This bug
has been fixed, FMODE_NOWAIT is respected by top vfs layer
