RFC: untangle and fix __blkdev_issue_discard

[Christoph Hellwig]

Hi all,

this tries to address the block for-next oops Chandan reported on XFS.
I can't actually reproduce it unfortunately, but this series should
sort it out by movign the fatal_signal_pending check out of all but
the ioctl path.  The write_zeroes and secure_erase path will need
similar treatment eventually.

Test with blktests and the xfstests discard group for xfs only. Note that
the latter has a pre-existing regression in generic/500 that I'll look
into in a bit.

Diffstat:
 block/blk-lib.c                   |   78 +++++++++++++-------------------------
 block/ioctl.c                     |   13 ++++--
 drivers/md/dm-thin.c              |    5 +-
 drivers/md/md.c                   |    6 +-
 drivers/nvme/target/io-cmd-bdev.c |   16 ++-----
 fs/ext4/mballoc.c                 |   16 ++++---
 fs/f2fs/segment.c                 |   10 ++--
 fs/xfs/xfs_discard.c              |   47 +++++++---------------
 fs/xfs/xfs_discard.h              |    2 
 include/linux/blkdev.h            |    4 -
 10 files changed, 84 insertions(+), 113 deletions(-)