Re: [PATCH v6 12/15] xfs: require mmap lock for xfs_break_layouts()

Darrick J. Wong
2018-03-19T17:34:35Z

On Thu, Mar 15, 2018 at 08:52:29AM -0700, Dan Williams wrote:
> In preparation for adding coordination between truncate operations and
> busy dax-pages, extend xfs_break_layouts() to assume it must be called
> with the mmap lock held. This locking scheme will be required for
> coordinating the break of 'dax layouts' (non-idle dax (ZONE_DEVICE)
> pages mapped into the file's address space).

If I'm reading this right, you've added a requirement (for xfs anyway)
that we have to have grabbed MMAPLOCK_EXCL before calling break_layout()
so that the layout breaking process will block until active dmas have
finished.

In 4.16 we added xfs_iolock_two_inodes_and_break_layout (in
xfs_reflink.c) to break pnfs leases for files that are about to be
reflinked (since pnfs and reflink aren't compatible either). I think
that function will have to be adapted to take the appropriate mmap locks
too -- definitely the exclusive mmap lock for the destination file
because we anticipate punching out blocks. I'm not sure about the
source file; I think taking the shared mmap lock is fine for that?

--D

>
> Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Dave Chinner <david@fromorbit.com>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/xfs/xfs_file.c | 14 +++++++++-----
> fs/xfs/xfs_ioctl.c | 5 +----
> fs/xfs/xfs_iops.c | 10 +++++++---
> fs/xfs/xfs_pnfs.c | 6 ++++--
> 4 files changed, 21 insertions(+), 14 deletions(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 9ea08326f876..ba969019bf26 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -350,9 +350,16 @@ xfs_file_aio_write_checks(
> if (error <= 0)
> return error;
>
> + xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
> + *iolock |= XFS_MMAPLOCK_EXCL;
> error = xfs_break_layouts(inode, iolock);
> - if (error)
> + if (error) {
> + *iolock &= ~XFS_MMAPLOCK_EXCL;
> + xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
> return error;
> + }
> + xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
> + *iolock &= ~XFS_MMAPLOCK_EXCL;
>
> /*
> * For changing security info in file_remove_privs() we need i_rwsem
> @@ -768,7 +775,7 @@ xfs_file_fallocate(
> struct xfs_inode *ip = XFS_I(inode);
> long error;
> enum xfs_prealloc_flags flags = 0;
> - uint iolock = XFS_IOLOCK_EXCL;
> + uint iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
> loff_t new_size = 0;
> bool do_file_insert = false;
>
> @@ -782,9 +789,6 @@ xfs_file_fallocate(
> if (error)
> goto out_unlock;
>
> - xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
> - iolock |= XFS_MMAPLOCK_EXCL;
> -
> if (mode & FALLOC_FL_PUNCH_HOLE) {
> error = xfs_free_file_space(ip, offset, len);
> if (error)
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 89fb1eb80aae..4151fade4bb1 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -614,7 +614,7 @@ xfs_ioc_space(
> struct xfs_inode *ip = XFS_I(inode);
> struct iattr iattr;
> enum xfs_prealloc_flags flags = 0;
> - uint iolock = XFS_IOLOCK_EXCL;
> + uint iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
> int error;
>
> /*
> @@ -648,9 +648,6 @@ xfs_ioc_space(
> if (error)
> goto out_unlock;
>
> - xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
> - iolock |= XFS_MMAPLOCK_EXCL;
> -
> switch (bf->l_whence) {
> case 0: /*SEEK_SET*/
> break;
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 951e84df5576..d23aa08426f9 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1028,13 +1028,17 @@ xfs_vn_setattr(
>
> if (iattr->ia_valid & ATTR_SIZE) {
> struct xfs_inode *ip = XFS_I(d_inode(dentry));
> - uint iolock = XFS_IOLOCK_EXCL;
> + uint iolock;
> +
> + xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
> + iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
>
> error = xfs_break_layouts(d_inode(dentry), &iolock);
> - if (error)
> + if (error) {
> + xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
> return error;
> + }
>
> - xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
> error = xfs_vn_setattr_size(dentry, iattr);
> xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
> } else {
> diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
> index aa6c5c193f45..9fe661c2d59c 100644
> --- a/fs/xfs/xfs_pnfs.c
> +++ b/fs/xfs/xfs_pnfs.c
> @@ -38,12 +38,14 @@ xfs_break_layouts(
> struct xfs_inode *ip = XFS_I(inode);
> int error;
>
> - ASSERT(xfs_isilocked(ip, XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL));
> + ASSERT(xfs_isilocked(ip, XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL
> + | XFS_MMAPLOCK_EXCL));
>
> while ((error = break_layout(inode, false) == -EWOULDBLOCK)) {
> xfs_iunlock(ip, *iolock);
> error = break_layout(inode, true);
> - *iolock = XFS_IOLOCK_EXCL;
> + *iolock &= ~XFS_IOLOCK_SHARED;
> + *iolock |= XFS_IOLOCK_EXCL;
> xfs_ilock(ip, *iolock);
> }
>
>
> --
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