[PATCH v2 0/3] Avert possible deadlock with splice() and fanotify

[Amir Goldstein <amir73il@gmail.com>]

Christian,

Josef has helped me see the light and figure out how to avoid the
possible deadlock, which involves:
- splice() from source file in a loop mounted fs to dest file in
  a host fs, where the loop image file is
- fsfreeze on host fs
- write to host fs in context of fanotify permission event handler
  (FAN_ACCESS_PERM) on the splice source file

The first patch should not be changing any logic.
I only build tested the ceph patch, so hoping to get an
Acked-by/Tested-by from Jeff.

The following patches rids us of the deadlock by not holding
file_start_write() while reading from splice source file in the
cases where source and destination can be on different arbitrary
filesystems.

The patches apply and tested on top of vfs.rw branch.

Thanks,
Amir.

Changes since v1:
- Add patch to deal with nfsd/ksmbd server-side-copy
- Shorten helper name to splice_file_range()
- Added assertion for flags value in generic_copy_file_range()
- Added RVB from Jan

Amir Goldstein (3):
  fs: fork splice_file_range() from do_splice_direct()
  fs: move file_start_write() into direct_splice_actor()
  fs: use do_splice_direct() for nfsd/ksmbd server-side-copy

 fs/ceph/file.c         |  9 +++--
 fs/overlayfs/copy_up.c |  2 -
 fs/read_write.c        | 42 +++++++++++---------
 fs/splice.c            | 88 +++++++++++++++++++++++++++++++-----------
 include/linux/fs.h     |  2 -
 include/linux/splice.h | 13 ++++---
 6 files changed, 103 insertions(+), 53 deletions(-)

-- 
2.34.1