Re: [PATCH v6 07/26] fs/dax: Ensure all pages are idle prior to filesystem unmount

Darrick J. Wong
2025-01-10T16:50:20Z

On Fri, Jan 10, 2025 at 05:00:35PM +1100, Alistair Popple wrote:
> File systems call dax_break_mapping() prior to reallocating file
> system blocks to ensure the page is not undergoing any DMA or other
> accesses. Generally this is needed when a file is truncated to ensure
> that if a block is reallocated nothing is writing to it. However
> filesystems currently don't call this when an FS DAX inode is evicted.
>
> This can cause problems when the file system is unmounted as a page
> can continue to be under going DMA or other remote access after
> unmount. This means if the file system is remounted any truncate or
> other operation which requires the underlying file system block to be
> freed will not wait for the remote access to complete. Therefore a
> busy block may be reallocated to a new file leading to corruption.
>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>
> ---
>
> Changes for v5:
>
> - Don't wait for pages to be idle in non-DAX mappings
> ---
> fs/dax.c | 29 +++++++++++++++++++++++++++++
> fs/ext4/inode.c | 32 ++++++++++++++------------------
> fs/xfs/xfs_inode.c | 9 +++++++++
> fs/xfs/xfs_inode.h | 1 +
> fs/xfs/xfs_super.c | 18 ++++++++++++++++++
> include/linux/dax.h | 2 ++
> 6 files changed, 73 insertions(+), 18 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 7008a73..4e49cc4 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -883,6 +883,14 @@ static int wait_page_idle(struct page *page,
> TASK_INTERRUPTIBLE, 0, 0, cb(inode));
> }
>
> +static void wait_page_idle_uninterruptible(struct page *page,
> + void (cb)(struct inode *),
> + struct inode *inode)
> +{
> + ___wait_var_event(page, page_ref_count(page) == 1,
> + TASK_UNINTERRUPTIBLE, 0, 0, cb(inode));
> +}
> +
> /*
> * Unmaps the inode and waits for any DMA to complete prior to deleting the
> * DAX mapping entries for the range.
> @@ -911,6 +919,27 @@ int dax_break_mapping(struct inode *inode, loff_t start, loff_t end,
> }
> EXPORT_SYMBOL_GPL(dax_break_mapping);
>
> +void dax_break_mapping_uninterruptible(struct inode *inode,
> + void (cb)(struct inode *))
> +{
> + struct page *page;
> +
> + if (!dax_mapping(inode->i_mapping))
> + return;
> +
> + do {
> + page = dax_layout_busy_page_range(inode->i_mapping, 0,
> + LLONG_MAX);
> + if (!page)
> + break;
> +
> + wait_page_idle_uninterruptible(page, cb, inode);
> + } while (true);
> +
> + dax_delete_mapping_range(inode->i_mapping, 0, LLONG_MAX);
> +}
> +EXPORT_SYMBOL_GPL(dax_break_mapping_uninterruptible);
> +
> /*
> * Invalidate DAX entry if it is clean.
> */
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index ee8e83f..fa35161 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -163,6 +163,18 @@ int ext4_inode_is_fast_symlink(struct inode *inode)
> (inode->i_size < EXT4_N_BLOCKS * 4);
> }
>
> +static void ext4_wait_dax_page(struct inode *inode)
> +{
> + filemap_invalidate_unlock(inode->i_mapping);
> + schedule();
> + filemap_invalidate_lock(inode->i_mapping);
> +}
> +
> +int ext4_break_layouts(struct inode *inode)
> +{
> + return dax_break_mapping_inode(inode, ext4_wait_dax_page);
> +}
> +
> /*
> * Called at the last iput() if i_nlink is zero.
> */
> @@ -181,6 +193,8 @@ void ext4_evict_inode(struct inode *inode)
>
> trace_ext4_evict_inode(inode);
>
> + dax_break_mapping_uninterruptible(inode, ext4_wait_dax_page);
> +
> if (EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL)
> ext4_evict_ea_inode(inode);
> if (inode->i_nlink) {
> @@ -3902,24 +3916,6 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
> return ret;
> }
>
> -static void ext4_wait_dax_page(struct inode *inode)
> -{
> - filemap_invalidate_unlock(inode->i_mapping);
> - schedule();
> - filemap_invalidate_lock(inode->i_mapping);
> -}
> -
> -int ext4_break_layouts(struct inode *inode)
> -{
> - struct page *page;
> - int error;
> -
> - if (WARN_ON_ONCE(!rwsem_is_locked(&inode->i_mapping->invalidate_lock)))
> - return -EINVAL;
> -
> - return dax_break_mapping_inode(inode, ext4_wait_dax_page);
> -}
> -
> /*
> * ext4_punch_hole: punches a hole in a file by releasing the blocks
> * associated with the given offset and length
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 4410b42..c7ec5ab 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -2997,6 +2997,15 @@ xfs_break_dax_layouts(
> return dax_break_mapping_inode(inode, xfs_wait_dax_page);
> }
>
> +void
> +xfs_break_dax_layouts_uninterruptible(
> + struct inode *inode)
> +{
> + xfs_assert_ilocked(XFS_I(inode), XFS_MMAPLOCK_EXCL);
> +
> + dax_break_mapping_uninterruptible(inode, xfs_wait_dax_page);
> +}
> +
> int
> xfs_break_layouts(
> struct inode *inode,
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index c4f03f6..613797a 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -594,6 +594,7 @@ xfs_itruncate_extents(
> }
>
> int xfs_break_dax_layouts(struct inode *inode);
> +void xfs_break_dax_layouts_uninterruptible(struct inode *inode);
> int xfs_break_layouts(struct inode *inode, uint *iolock,
> enum layout_break_reason reason);
>
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 8524b9d..73ec060 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -751,6 +751,23 @@ xfs_fs_drop_inode(
> return generic_drop_inode(inode);
> }
>
> +STATIC void
> +xfs_fs_evict_inode(
> + struct inode *inode)
> +{
> + struct xfs_inode *ip = XFS_I(inode);
> + uint iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
> +
> + if (IS_DAX(inode)) {
> + xfs_ilock(ip, iolock);
> + xfs_break_dax_layouts_uninterruptible(inode);
> + xfs_iunlock(ip, iolock);

If we're evicting the inode, why is it necessary to take i_rwsem and the
mmap invalidation lock? Shouldn't the evicting thread be the only one
with access to this inode?

--D

> + }
> +
> + truncate_inode_pages_final(&inode->i_data);
> + clear_inode(inode);
> +}
> +
> static void
> xfs_mount_free(
> struct xfs_mount *mp)
> @@ -1189,6 +1206,7 @@ static const struct super_operations xfs_super_operations = {
> .destroy_inode = xfs_fs_destroy_inode,
> .dirty_inode = xfs_fs_dirty_inode,
> .drop_inode = xfs_fs_drop_inode,
> + .evict_inode = xfs_fs_evict_inode,
> .put_super = xfs_fs_put_super,
> .sync_fs = xfs_fs_sync_fs,
> .freeze_fs = xfs_fs_freeze,
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index ef9e02c..7c3773f 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -274,6 +274,8 @@ static inline int __must_check dax_break_mapping_inode(struct inode *inode,
> {
> return dax_break_mapping(inode, 0, LLONG_MAX, cb);
> }
> +void dax_break_mapping_uninterruptible(struct inode *inode,
> + void (cb)(struct inode *));
> int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> struct inode *dest, loff_t destoff,
> loff_t len, bool *is_same,
> --
> git-series 0.9.1
>