[0/4] Introduce a mmap sem to deal with some mmap issues

Message

Josef Bacik Dec. 14, 2020, 6:19 p.m. UTC

Hello,

Both Filipe and I have found different issues that result in the same thing, we
need to be able to exclude mmap from happening in certain scenarios.  The
specifics are well described in the commit logs, but generally there's 2 issues

1) dedupe needs to validate that pages match, and since the validation is done
   outside of the extent lock we can race with mmap and dedupe pages that do not
   match.
2) We can deadlock in certain low metadata scenarios where we need to flush
   an ordered extent, but can't because mmap is holding the page lock.

These issues exist for remap and fallocate, so add an i_mmap_sem to allow us to
disallow mmap in these cases.  I'm still waiting on xfstests to finish with
this, but 2 hours in and no lockdep or deadlocks.  Thanks,

Josef Bacik (4):
  btrfs: add a i_mmap_lock to our inode
  btrfs: cleanup inode_lock/inode_unlock uses
  btrfs: exclude mmaps while doing remap
  btrfs: exclude mmap from happening during all fallocate operations

 fs/btrfs/btrfs_inode.h   |  1 +
 fs/btrfs/ctree.h         |  1 +
 fs/btrfs/delayed-inode.c |  4 ++--
 fs/btrfs/file.c          | 20 ++++++++++----------
 fs/btrfs/inode.c         | 10 ++++++++++
 fs/btrfs/ioctl.c         | 26 +++++++++++++-------------
 fs/btrfs/reflink.c       | 30 ++++++++++++++++++++++++------
 fs/btrfs/relocation.c    |  4 ++--
 8 files changed, 63 insertions(+), 33 deletions(-)

Comments

Christoph Hellwig Dec. 23, 2020, 8:19 a.m. UTC | #1

On Mon, Dec 14, 2020 at 01:19:37PM -0500, Josef Bacik wrote:
> These issues exist for remap and fallocate, so add an i_mmap_sem to allow us to
> disallow mmap in these cases.  I'm still waiting on xfstests to finish with
> this, but 2 hours in and no lockdep or deadlocks.  Thanks,

Any chance you could look into lifting it to the VFS and also convert
ext4 and XFS to the common scheme?