On Tue, May 02 2017, Ming Lei wrote:

On Tue, May 02, 2017 at 01:42:24PM +1000, NeilBrown wrote:

quoted

This patch converts bioset_create() and
bioset_create_nobvec() to not create a workqueue so
alloctions will never trigger punt_bios_to_rescuer().  It
also introduces bioset_create_rescued() and
bioset_create_nobvec_rescued() which preserve the old
behaviour.

All callers of bioset_create() and bioset_create_nobvec(),
that are inside block device drivers, are converted to the
_rescued() version.

The above comment about *_nobvec() need to be updated.

Yes - thanks.  I'll post an updated version.

quoted

biosets used by filesystems or other top-level users do not
need rescuing as the bio can never be queued behind other
bios.  This includes fs_bio_set, blkdev_dio_pool,
btrfs_bioset, xfs_ioend_bioset, drbd_md_io_bio_set,
and one allocated by target_core_iblock.c.

biosets used by md/raid to not need rescuing as
their usage was recently audited to revised to never
risk deadlock.

It is hoped that most, if not all, of the remaining biosets
can end up being the non-rescued version.

Signed-off-by: NeilBrown <redacted>
---
 block/bio.c               |   12 ++++++++++--
 block/blk-core.c          |    2 +-
 drivers/md/bcache/super.c |    6 ++++--
 drivers/md/dm-crypt.c     |    2 +-
 drivers/md/dm-io.c        |    2 +-
 drivers/md/dm.c           |    5 +++--
 include/linux/bio.h       |    1 +
 7 files changed, 21 insertions(+), 9 deletions(-)

DRBD can stack on block device too, so I guess it might need
BIOSET_NEED_RESCUER?

A bioset only needs a rescuer is an allocation is made from the bioset
inside a make_request_fn.
The bioset in DRBD is drbd_md_io_bio_set is used for metadata IO, and
I think it is only used in a worker thread, where rescuing cannot help.
But that is probably subtle enough that I should leave the removal
of the rescuer to a subsequent patch.
So I'll give DRBD the flag when I update the changelog comment.

Thanks,
NeilBrown