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Subject[PATCH v5 02/11] xfs, dax: introduce xfs_dax_aops
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In preparation for the dax implementation to start associating dax pages
to inodes via page->mapping, we need to provide a 'struct
address_space_operations' instance for dax. Otherwise, direct-I/O
triggers incorrect page cache assumptions and warnings like the
following:

WARNING: CPU: 27 PID: 1783 at fs/xfs/xfs_aops.c:1468
xfs_vm_set_page_dirty+0xf3/0x1b0 [xfs]
[..]
CPU: 27 PID: 1783 Comm: dma-collision Tainted: G O 4.15.0-rc2+ #984
[..]
Call Trace:
set_page_dirty_lock+0x40/0x60
bio_set_pages_dirty+0x37/0x50
iomap_dio_actor+0x2b7/0x3b0
? iomap_dio_zero+0x110/0x110
iomap_apply+0xa4/0x110
iomap_dio_rw+0x29e/0x3b0
? iomap_dio_zero+0x110/0x110
? xfs_file_dio_aio_read+0x7c/0x1a0 [xfs]
xfs_file_dio_aio_read+0x7c/0x1a0 [xfs]
xfs_file_read_iter+0xa0/0xc0 [xfs]
__vfs_read+0xf9/0x170
vfs_read+0xa6/0x150
SyS_pread64+0x93/0xb0
entry_SYSCALL_64_fastpath+0x1f/0x96

...where the default set_page_dirty() handler assumes that dirty state
is being tracked in 'struct page' flags.

Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
fs/dax.c | 27 +++++++++++++++++++++++++++
fs/xfs/xfs_aops.c | 7 +++++++
fs/xfs/xfs_aops.h | 1 +
fs/xfs/xfs_iops.c | 5 ++++-
include/linux/dax.h | 6 ++++++
5 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index b646a46e4d12..ba02772fccbc 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -46,6 +46,33 @@
#define PG_PMD_COLOUR ((PMD_SIZE >> PAGE_SHIFT) - 1)
#define PG_PMD_NR (PMD_SIZE >> PAGE_SHIFT)

+int dax_set_page_dirty(struct page *page)
+{
+ /*
+ * Unlike __set_page_dirty_no_writeback that handles dirty page
+ * tracking in the page object, dax does all dirty tracking in
+ * the inode address_space in response to mkwrite faults. In the
+ * dax case we only need to worry about potentially dirty CPU
+ * caches, not dirty page cache pages to write back.
+ *
+ * This callback is defined to prevent fallback to
+ * __set_page_dirty_buffers() in set_page_dirty().
+ */
+ return 0;
+}
+EXPORT_SYMBOL(dax_set_page_dirty);
+
+void dax_invalidatepage(struct page *page, unsigned int offset,
+ unsigned int length)
+{
+ /*
+ * There is no page cache to invalidate in the dax case, however
+ * we need this callback defined to prevent falling back to
+ * block_invalidatepage() in do_invalidatepage().
+ */
+}
+EXPORT_SYMBOL(dax_invalidatepage);
+
static wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];

static int __init init_dax_wait_table(void)
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 9c6a830da0ee..5788b680fa01 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1505,3 +1505,10 @@ const struct address_space_operations xfs_address_space_operations = {
.is_partially_uptodate = block_is_partially_uptodate,
.error_remove_page = generic_error_remove_page,
};
+
+const struct address_space_operations xfs_dax_aops = {
+ .writepages = xfs_vm_writepages,
+ .direct_IO = xfs_vm_direct_IO,
+ .set_page_dirty = dax_set_page_dirty,
+ .invalidatepage = dax_invalidatepage,
+};
diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
index 88c85ea63da0..69346d460dfa 100644
--- a/fs/xfs/xfs_aops.h
+++ b/fs/xfs/xfs_aops.h
@@ -54,6 +54,7 @@ struct xfs_ioend {
};

extern const struct address_space_operations xfs_address_space_operations;
+extern const struct address_space_operations xfs_dax_aops;

int xfs_setfilesize(struct xfs_inode *ip, xfs_off_t offset, size_t size);

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 56475fcd76f2..951e84df5576 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1272,7 +1272,10 @@ xfs_setup_iops(
case S_IFREG:
inode->i_op = &xfs_inode_operations;
inode->i_fop = &xfs_file_operations;
- inode->i_mapping->a_ops = &xfs_address_space_operations;
+ if (IS_DAX(inode))
+ inode->i_mapping->a_ops = &xfs_dax_aops;
+ else
+ inode->i_mapping->a_ops = &xfs_address_space_operations;
break;
case S_IFDIR:
if (xfs_sb_version_hasasciici(&XFS_M(inode->i_sb)->m_sb))
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 0185ecdae135..3045c0d9c804 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -57,6 +57,9 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
}

struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
+int dax_set_page_dirty(struct page *page);
+void dax_invalidatepage(struct page *page, unsigned int offset,
+ unsigned int length);
#else
static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
{
@@ -76,6 +79,9 @@ static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
{
return NULL;
}
+
+#define dax_set_page_dirty NULL
+#define dax_invalidatepage NULL
#endif

int dax_read_lock(void);
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