Re: [PATCH v3 05/25] fs/dax: Create a common implementation to break DAX layouts

Alistair Popple
2024-11-22T03:39:14Z

John Hubbard <jhubbard@nvidia.com> writes:

> On 11/21/24 5:40 PM, Alistair Popple wrote:
>> Prior to freeing a block file systems supporting FS DAX must check
>> that the associated pages are both unmapped from user-space and not
>> undergoing DMA or other access from eg. get_user_pages(). This is
>> achieved by unmapping the file range and scanning the FS DAX
>> page-cache to see if any pages within the mapping have an elevated
>> refcount.
>> This is done using two functions - dax_layout_busy_page_range()
>> which
>> returns a page to wait for the refcount to become idle on. Rather than
>> open-code this introduce a common implementation to both unmap and
>> wait for the page to become idle.
>> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>> ---
>> fs/dax.c | 29 +++++++++++++++++++++++++++++
>> fs/ext4/inode.c | 10 +---------
>> fs/fuse/dax.c | 29 +++++------------------------
>> fs/xfs/xfs_inode.c | 23 +++++------------------
>> fs/xfs/xfs_inode.h | 2 +-
>> include/linux/dax.h | 7 +++++++
>> 6 files changed, 48 insertions(+), 52 deletions(-)
>> diff --git a/fs/dax.c b/fs/dax.c
>> index efc1d56..b1ad813 100644
>> --- a/fs/dax.c
>> +++ b/fs/dax.c
>> @@ -845,6 +845,35 @@ int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
>> return ret;
>> }
>> +static int wait_page_idle(struct page *page,
>> + void (cb)(struct inode *),
>> + struct inode *inode)
>> +{
>> + return ___wait_var_event(page, page_ref_count(page) == 1,
>> + TASK_INTERRUPTIBLE, 0, 0, cb(inode));
>> +}
>> +
>> +/*
>> + * Unmaps the inode and waits for any DMA to complete prior to deleting the
>> + * DAX mapping entries for the range.
>> + */
>> +int dax_break_mapping(struct inode *inode, loff_t start, loff_t end,
>> + void (cb)(struct inode *))
>> +{
>> + struct page *page;
>> + int error;
>> +
>> + do {
>> + page = dax_layout_busy_page_range(inode->i_mapping, start, end);
>> + if (!page)
>> + break;
>> +
>> + error = wait_page_idle(page, cb, inode);
>> + } while (error == 0);
>> +
>> + return error;
>> +}
>
> Hi Alistair!
>
> This needs to be EXPORT'ed. In fact so do two others, but I thought I'd
> reply at the exact point that the first fix needs to be inserted, which
> is here. And let you sprinkle the remaining two into the right patches.

Argh, thanks. I guess one of the kernel build bots will yell at me soon
enough... :-)

- Alistair

> The overall diff required for me to build the kernel with this series is:
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 0169b356b975..35e3c41eb517 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -921,6 +921,7 @@ void dax_delete_mapping_range(struct address_space *mapping,
> }
> xas_unlock_irq(&xas);
> }
> +EXPORT_SYMBOL_GPL(dax_delete_mapping_range);
> static int wait_page_idle(struct page *page,
> void (cb)(struct inode *),
> @@ -961,6 +962,7 @@ int dax_break_mapping(struct inode *inode, loff_t start, loff_t end,
> return error;
> }
> +EXPORT_SYMBOL_GPL(dax_break_mapping);
> void dax_break_mapping_uninterruptible(struct inode *inode,
> void (cb)(struct inode *))
> @@ -979,6 +981,7 @@ void dax_break_mapping_uninterruptible(struct inode *inode,
> if (!page)
> dax_delete_mapping_range(inode->i_mapping, 0, LLONG_MAX);
> }
> +EXPORT_SYMBOL_GPL(dax_break_mapping_uninterruptible);
> /*
> * Invalidate DAX entry if it is clean.
>
>
> thanks,
> John Hubbard
>
>
>> +
>> /*
>> * Invalidate DAX entry if it is clean.
>> */
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index cf87c5b..d42c011 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -3885,15 +3885,7 @@ int ext4_break_layouts(struct inode *inode)
>> if (WARN_ON_ONCE(!rwsem_is_locked(&inode->i_mapping->invalidate_lock)))
>> return -EINVAL;
>> - do {
>> - page = dax_layout_busy_page(inode->i_mapping);
>> - if (!page)
>> - return 0;
>> -
>> - error = dax_wait_page_idle(page, ext4_wait_dax_page, inode);
>> - } while (error == 0);
>> -
>> - return error;
>> + return dax_break_mapping_inode(inode, ext4_wait_dax_page);
>> }
>> /*
>> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
>> index af436b5..2493f9c 100644
>> --- a/fs/fuse/dax.c
>> +++ b/fs/fuse/dax.c
>> @@ -665,38 +665,19 @@ static void fuse_wait_dax_page(struct inode *inode)
>> filemap_invalidate_lock(inode->i_mapping);
>> }
>> -/* Should be called with mapping->invalidate_lock held
>> exclusively */
>> -static int __fuse_dax_break_layouts(struct inode *inode, bool *retry,
>> - loff_t start, loff_t end)
>> -{
>> - struct page *page;
>> -
>> - page = dax_layout_busy_page_range(inode->i_mapping, start, end);
>> - if (!page)
>> - return 0;
>> -
>> - *retry = true;
>> - return dax_wait_page_idle(page, fuse_wait_dax_page, inode);
>> -}
>> -
>> -/* dmap_end == 0 leads to unmapping of whole file */
>> +/* Should be called with mapping->invalidate_lock held exclusively.
>> + * dmap_end == 0 leads to unmapping of whole file.
>> + */
>> int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start,
>> u64 dmap_end)
>> {
>> - bool retry;
>> - int ret;
>> -
>> - do {
>> - retry = false;
>> - ret = __fuse_dax_break_layouts(inode, &retry, dmap_start,
>> - dmap_end);
>> - } while (ret == 0 && retry);
>> if (!dmap_end) {
>> dmap_start = 0;
>> dmap_end = LLONG_MAX;
>> }
>> - return ret;
>> + return dax_break_mapping(inode, dmap_start, dmap_end,
>> + fuse_wait_dax_page);
>> }
>> ssize_t fuse_dax_read_iter(struct kiocb *iocb, struct iov_iter
>> *to)
>> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
>> index eb12123..120597a 100644
>> --- a/fs/xfs/xfs_inode.c
>> +++ b/fs/xfs/xfs_inode.c
>> @@ -2704,21 +2704,17 @@ xfs_mmaplock_two_inodes_and_break_dax_layout(
>> struct xfs_inode *ip2)
>> {
>> int error;
>> - bool retry;
>> struct page *page;
>> if (ip1->i_ino > ip2->i_ino)
>> swap(ip1, ip2);
>> again:
>> - retry = false;
>> /* Lock the first inode */
>> xfs_ilock(ip1, XFS_MMAPLOCK_EXCL);
>> - error = xfs_break_dax_layouts(VFS_I(ip1), &retry);
>> - if (error || retry) {
>> + error = xfs_break_dax_layouts(VFS_I(ip1));
>> + if (error) {
>> xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
>> - if (error == 0 && retry)
>> - goto again;
>> return error;
>> }
>> @@ -2977,19 +2973,11 @@ xfs_wait_dax_page(
>> int
>> xfs_break_dax_layouts(
>> - struct inode *inode,
>> - bool *retry)
>> + struct inode *inode)
>> {
>> - struct page *page;
>> -
>> xfs_assert_ilocked(XFS_I(inode), XFS_MMAPLOCK_EXCL);
>> - page = dax_layout_busy_page(inode->i_mapping);
>> - if (!page)
>> - return 0;
>> -
>> - *retry = true;
>> - return dax_wait_page_idle(page, xfs_wait_dax_page, inode);
>> + return dax_break_mapping_inode(inode, xfs_wait_dax_page);
>> }
>> int
>> @@ -3007,8 +2995,7 @@ xfs_break_layouts(
>> retry = false;
>> switch (reason) {
>> case BREAK_UNMAP:
>> - error = xfs_break_dax_layouts(inode, &retry);
>> - if (error || retry)
>> + if (xfs_break_dax_layouts(inode))
>> break;
>> fallthrough;
>> case BREAK_WRITE:
>> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
>> index 97ed912..0db27ba 100644
>> --- a/fs/xfs/xfs_inode.h
>> +++ b/fs/xfs/xfs_inode.h
>> @@ -564,7 +564,7 @@ xfs_itruncate_extents(
>> return xfs_itruncate_extents_flags(tpp, ip, whichfork, new_size, 0);
>> }
>> -int xfs_break_dax_layouts(struct inode *inode, bool
>> *retry);
>> +int xfs_break_dax_layouts(struct inode *inode);
>> int xfs_break_layouts(struct inode *inode, uint *iolock,
>> enum layout_break_reason reason);
>> diff --git a/include/linux/dax.h b/include/linux/dax.h
>> index 773dfc4..7419c88 100644
>> --- a/include/linux/dax.h
>> +++ b/include/linux/dax.h
>> @@ -257,6 +257,13 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
>> int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
>> int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
>> pgoff_t index);
>> +int __must_check dax_break_mapping(struct inode *inode, loff_t start,
>> + loff_t end, void (cb)(struct inode *));
>> +static inline int __must_check dax_break_mapping_inode(struct inode *inode,
>> + void (cb)(struct inode *))
>> +{
>> + return dax_break_mapping(inode, 0, LLONG_MAX, cb);
>> +}
>> int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
>> struct inode *dest, loff_t destoff,
>> loff_t len, bool *is_same,