On Mon, 24 Jan 2022 at 03:53, NeilBrown <neilb@xxxxxxx> wrote:
>
> 1/ Taking the i_rwsem for swap IO triggers lockdep warnings regarding
> possible deadlocks with "fs_reclaim". These deadlocks could, I believe,
> eventuate if a buffered read on the swapfile was attempted.
>
> We don't need coherence with the page cache for a swap file, and
> buffered writes are forbidden anyway. There is no other need for
> i_rwsem during direct IO. So never take it for swap_rw()
>
> 2/ generic_write_checks() explicitly forbids writes to swap, and
> performs checks that are not needed for swap. So bypass it
> for swap_rw().
>
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> fs/nfs/direct.c | 30 +++++++++++++++++++++---------
> fs/nfs/file.c | 4 ++--
> include/linux/nfs_fs.h | 4 ++--
> 3 files changed, 25 insertions(+), 13 deletions(-)
>
...
> @@ -943,7 +954,8 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter)
> pos >> PAGE_SHIFT, end);
> }
>
> - nfs_end_io_direct(inode);
> + if (!swap)
> + nfs_end_io_direct(inode);
Just above this code diff, there is;
if (mapping->nrpages) {
invalidate_inode_pages2_range(mapping,
pos >> PAGE_SHIFT, end);
}
This invalidation looks strange/wrong for a NFS swap write. Should it
be disabled for the swap case?
Cheers,
Mark
