[PATCH 1/2] block: revert runtime dax control of the raw block device

[Dan Williams]

Dynamically enabling DAX requires that the page cache first be flushed
and invalidated.  This must occur atomically with the change of DAX mode
otherwise we confuse the fsync/msync tracking and violate data
durability guarantees.  Eliminate the possibilty of DAX-disabled to
DAX-enabled transitions for now and revisit this for the next cycle.

Cc: Jan Kara <jack@xxxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 block/ioctl.c           |   38 --------------------------------------
 fs/block_dev.c          |   28 ----------------------------
 include/linux/fs.h      |    3 ---
 include/uapi/linux/fs.h |    1 -
 4 files changed, 70 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index 77f5d17779d6..d8996bbd7f12 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -434,42 +434,6 @@ bool blkdev_dax_capable(struct block_device *bdev)
 
 	return true;
 }
-
-static int blkdev_daxset(struct block_device *bdev, unsigned long argp)
-{
-	unsigned long arg;
-	int rc = 0;
-
-	if (!capable(CAP_SYS_ADMIN))
-		return -EACCES;
-
-	if (get_user(arg, (int __user *)(argp)))
-		return -EFAULT;
-	arg = !!arg;
-	if (arg == !!(bdev->bd_inode->i_flags & S_DAX))
-		return 0;
-
-	if (arg)
-		arg = S_DAX;
-
-	if (arg && !blkdev_dax_capable(bdev))
-		return -ENOTTY;
-
-	inode_lock(bdev->bd_inode);
-	if (bdev->bd_map_count == 0)
-		inode_set_flags(bdev->bd_inode, arg, S_DAX);
-	else
-		rc = -EBUSY;
-	inode_unlock(bdev->bd_inode);
-	return rc;
-}
-#else
-static int blkdev_daxset(struct block_device *bdev, int arg)
-{
-	if (arg)
-		return -ENOTTY;
-	return 0;
-}
 #endif
 
 static int blkdev_flushbuf(struct block_device *bdev, fmode_t mode,
@@ -634,8 +598,6 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 	case BLKTRACESETUP:
 	case BLKTRACETEARDOWN:
 		return blk_trace_ioctl(bdev, cmd, argp);
-	case BLKDAXSET:
-		return blkdev_daxset(bdev, arg);
 	case BLKDAXGET:
 		return put_int(arg, !!(bdev->bd_inode->i_flags & S_DAX));
 		break;
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 7b9cd49622b1..afb437484362 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1736,37 +1736,13 @@ static int blkdev_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
 	return __dax_pmd_fault(vma, addr, pmd, flags, blkdev_get_block, NULL);
 }
 
-static void blkdev_vm_open(struct vm_area_struct *vma)
-{
-	struct inode *bd_inode = bdev_file_inode(vma->vm_file);
-	struct block_device *bdev = I_BDEV(bd_inode);
-
-	inode_lock(bd_inode);
-	bdev->bd_map_count++;
-	inode_unlock(bd_inode);
-}
-
-static void blkdev_vm_close(struct vm_area_struct *vma)
-{
-	struct inode *bd_inode = bdev_file_inode(vma->vm_file);
-	struct block_device *bdev = I_BDEV(bd_inode);
-
-	inode_lock(bd_inode);
-	bdev->bd_map_count--;
-	inode_unlock(bd_inode);
-}
-
 static const struct vm_operations_struct blkdev_dax_vm_ops = {
-	.open		= blkdev_vm_open,
-	.close		= blkdev_vm_close,
 	.fault		= blkdev_dax_fault,
 	.pmd_fault	= blkdev_dax_pmd_fault,
 	.pfn_mkwrite	= blkdev_dax_fault,
 };
 
 static const struct vm_operations_struct blkdev_default_vm_ops = {
-	.open		= blkdev_vm_open,
-	.close		= blkdev_vm_close,
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
 };
@@ -1774,18 +1750,14 @@ static const struct vm_operations_struct blkdev_default_vm_ops = {
 static int blkdev_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct inode *bd_inode = bdev_file_inode(file);
-	struct block_device *bdev = I_BDEV(bd_inode);
 
 	file_accessed(file);
-	inode_lock(bd_inode);
-	bdev->bd_map_count++;
 	if (IS_DAX(bd_inode)) {
 		vma->vm_ops = &blkdev_dax_vm_ops;
 		vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
 	} else {
 		vma->vm_ops = &blkdev_default_vm_ops;
 	}
-	inode_unlock(bd_inode);
 
 	return 0;
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b10002d4a5f5..ae681002100a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -484,9 +484,6 @@ struct block_device {
 	int			bd_fsfreeze_count;
 	/* Mutex for freeze */
 	struct mutex		bd_fsfreeze_mutex;
-#ifdef CONFIG_FS_DAX
-	int			bd_map_count;
-#endif
 };
 
 /*
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 41e0433b4a83..149bec83a907 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -222,7 +222,6 @@ struct fsxattr {
 #define BLKSECDISCARD _IO(0x12,125)
 #define BLKROTATIONAL _IO(0x12,126)
 #define BLKZEROOUT _IO(0x12,127)
-#define BLKDAXSET _IO(0x12,128)
 #define BLKDAXGET _IO(0x12,129)
 
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */