Date:   Thu, 1 Feb 2018 17:08:36 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-xfs@...r.kernel.org, ross.zwisler@...ux.intel.com,
        linux-ext4@...r.kernel.org, dan.j.williams@...el.com,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 2 2/2] xfs: fix rt_dev usage for DAX


On 02/01/2018 04:28 PM, Darrick J. Wong wrote:
>> [PATCH 2 2/2] xfs: fix rt_dev usage for DAX
> 
> "[PATCH v2 2/2]" to distinguish the version number from the patch number
> more explicitly.
> 
> On Thu, Feb 01, 2018 at 01:33:05PM -0700, Dave Jiang wrote:
>> When using realtime device (rtdev) with xfs where the data device is not
>> DAX capable, two issues arise. One is when data device is not DAX but the
>> realtime device is DAX capable, we currently disable DAX.
>> After passing this check, we are also not marking the inode as DAX capable.
>> This change will allow DAX enabled if the data device or the realtime
>> device is DAX capable. S_DAX will be marked for the inode if the file is
>> residing on a DAX capable device. This will prevent the case of rtdev is not
>> DAX and data device is DAX to create realtime files.
>>
>> Signed-off-by: Dave Jiang <dave.jiang@...el.com>
>> Reported-by: Darrick Wong <darrick.wong@...cle.com>
>> ---
>>  fs/xfs/xfs_iops.c  |    3 ++-
>>  fs/xfs/xfs_super.c |    9 ++++++++-
>>  2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
>> index 56475fcd76f2..ab352c325301 100644
>> --- a/fs/xfs/xfs_iops.c
>> +++ b/fs/xfs/xfs_iops.c
>> @@ -1204,7 +1204,8 @@ xfs_diflags_to_iflags(
>>  	    ip->i_mount->m_sb.sb_blocksize == PAGE_SIZE &&
>>  	    !xfs_is_reflink_inode(ip) &&
>>  	    (ip->i_mount->m_flags & XFS_MOUNT_DAX ||
>> -	     ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
>> +	     ip->i_d.di_flags2 & XFS_DIFLAG2_DAX) &&
>> +	    blk_queue_dax(bdev_get_queue(inode->i_sb->s_bdev)))
> 
> inode->i_sb->s_bdev is the data device bdev, so if the inode is a
> realtime file, we're checking the wrong device for daxiness, I think.
> 
> Maybe this whole ugly switch statement should get turned into a helper
> function?
> 
> xfs_ioctl_setattr_dax_invalidate needs to pick the right bdev to check.
> 
>>  		inode->i_flags |= S_DAX;
>>  }
>>  
>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
>> index e8a687232614..5ac478924dce 100644
>> --- a/fs/xfs/xfs_super.c
>> +++ b/fs/xfs/xfs_super.c
>> @@ -1649,11 +1649,18 @@ xfs_fs_fill_super(
>>  		sb->s_flags |= SB_I_VERSION;
>>  
>>  	if (mp->m_flags & XFS_MOUNT_DAX) {
>> +		bool rtdev_is_dax = false;
>> +
>>  		xfs_warn(mp,
>>  		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
>>  
>> +		if (mp->m_rtdev_targp->bt_daxdev)
>> +			if (bdev_dax_supported(mp->m_rtdev_targp->bt_bdev,
>> +					      sb->s_blocksize) == 0)
>> +				rtdev_is_dax = true;
>> +
>>  		error = bdev_dax_supported(sb->s_bdev, sb->s_blocksize);
>> -		if (error) {
>> +		if (error && !rtdev_is_dax) {
>>  			xfs_alert(mp,
>>  			"DAX unsupported by block device. Turning off DAX.");
>>  			mp->m_flags &= ~XFS_MOUNT_DAX;
>>
>> --
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> 
> Does the following patch fix everything for you?
> 
> (Note that we can't switch S_DAX on a running fs so you have to remount
> the whole fs after setting the dax flag...)

Yes this passes my tests. However it looks like Dave Chinner has
additional concerns with regards to changing the S_DAX flag dynamically?


> 
> --D
> 
> --------------------
> 
> fs: allow per-device dax status checking for filesystems
> 
> Refactor __bdev_dax_supported into a sb_dax_supported helper for
> single-bdev filesystems and a regular bdev_dax_supported that takes a
> bdev parameter.  This enables multi-device filesystems like xfs to check
> that a dax device can work for the particular filesystem.  Once that's
> in place, actually fix all the parts of XFS where we need to be able to
> distinguish between datadev and rtdev.
> 
> This patch fixes the problem where we screw up the dax support checking
> in xfs if the datadev and rtdev have different dax capabilities.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
>  drivers/dax/super.c |    9 +++++----
>  fs/ext2/super.c     |    2 +-
>  fs/ext4/super.c     |    2 +-
>  fs/xfs/xfs_ioctl.c  |    3 ++-
>  fs/xfs/xfs_iops.c   |   30 +++++++++++++++++++++++++-----
>  fs/xfs/xfs_super.c  |   11 +++++++++--
>  include/linux/dax.h |   16 ++++++++++++----
>  7 files changed, 55 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 3ec8046..c4db84f 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -72,8 +72,9 @@ EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
>  #endif
>  
>  /**
> - * __bdev_dax_supported() - Check if the device supports dax for filesystem
> + * bdev_dax_supported() - Check if the device supports dax for filesystem
>   * @sb: The superblock of the device
> + * @bdev: block device to check
>   * @blocksize: The block size of the device
>   *
>   * This is a library function for filesystems to check if the block device
> @@ -81,9 +82,9 @@ EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
>   *
>   * Return: negative errno if unsupported, 0 if supported.
>   */
> -int __bdev_dax_supported(struct super_block *sb, int blocksize)
> +int bdev_dax_supported(struct super_block *sb, struct block_device *bdev,
> +		       int blocksize)
>  {
> -	struct block_device *bdev = sb->s_bdev;
>  	struct dax_device *dax_dev;
>  	pgoff_t pgoff;
>  	int err, id;
> @@ -125,7 +126,7 @@ int __bdev_dax_supported(struct super_block *sb, int blocksize)
>  
>  	return 0;
>  }
> -EXPORT_SYMBOL_GPL(__bdev_dax_supported);
> +EXPORT_SYMBOL_GPL(bdev_dax_supported);
>  #endif
>  
>  enum dax_device_flags {
> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 7646818..6556993 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -958,7 +958,7 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
>  	blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
>  
>  	if (sbi->s_mount_opt & EXT2_MOUNT_DAX) {
> -		err = bdev_dax_supported(sb, blocksize);
> +		err = sb_dax_supported(sb, blocksize);
>  		if (err)
>  			goto failed_mount;
>  	}
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 7c46693..804a2d6 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3712,7 +3712,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  					" that may contain inline data");
>  			goto failed_mount;
>  		}
> -		err = bdev_dax_supported(sb, blocksize);
> +		err = sb_dax_supported(sb, blocksize);
>  		if (err)
>  			goto failed_mount;
>  	}
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 89fb1eb..277355f 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1103,7 +1103,8 @@ xfs_ioctl_setattr_dax_invalidate(
>  	if (fa->fsx_xflags & FS_XFLAG_DAX) {
>  		if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)))
>  			return -EINVAL;
> -		if (bdev_dax_supported(sb, sb->s_blocksize) < 0)
> +		if (bdev_dax_supported(sb, xfs_find_bdev_for_inode(VFS_I(ip)),
> +				sb->s_blocksize) < 0)
>  			return -EINVAL;
>  	}
>  
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 56475fc..66cd61c 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1182,6 +1182,30 @@ static const struct inode_operations xfs_inline_symlink_inode_operations = {
>  	.update_time		= xfs_vn_update_time,
>  };
>  
> +/* Figure out if this file actually supports DAX. */
> +static bool
> +xfs_inode_supports_dax(
> +	struct xfs_inode	*ip)
> +{
> +	struct xfs_mount	*mp = ip->i_mount;
> +
> +	/* Only supported on non-reflinked files. */
> +	if (!S_ISREG(VFS_I(ip)->i_mode) || xfs_is_reflink_inode(ip))
> +		return false;
> +
> +	/* DAX mount option or DAX iflag must be set. */
> +	if (!(mp->m_flags & XFS_MOUNT_DAX) &&
> +	    !(ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
> +		return false;
> +
> +	/* Block size must match page size */
> +	if (mp->m_sb.sb_blocksize != PAGE_SIZE)
> +		return false;
> +
> +	/* Device has to support DAX too. */
> +	return xfs_find_daxdev_for_inode(VFS_I(ip)) != NULL;
> +}
> +
>  STATIC void
>  xfs_diflags_to_iflags(
>  	struct inode		*inode,
> @@ -1200,11 +1224,7 @@ xfs_diflags_to_iflags(
>  		inode->i_flags |= S_SYNC;
>  	if (flags & XFS_DIFLAG_NOATIME)
>  		inode->i_flags |= S_NOATIME;
> -	if (S_ISREG(inode->i_mode) &&
> -	    ip->i_mount->m_sb.sb_blocksize == PAGE_SIZE &&
> -	    !xfs_is_reflink_inode(ip) &&
> -	    (ip->i_mount->m_flags & XFS_MOUNT_DAX ||
> -	     ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
> +	if (xfs_inode_supports_dax(ip))
>  		inode->i_flags |= S_DAX;
>  }
>  
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 6f1b917..c115bc7 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1692,11 +1692,18 @@ xfs_fs_fill_super(
>  		sb->s_flags |= SB_I_VERSION;
>  
>  	if (mp->m_flags & XFS_MOUNT_DAX) {
> +		int	error2 = 0;
> +
>  		xfs_warn(mp,
>  		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
>  
> -		error = bdev_dax_supported(sb, sb->s_blocksize);
> -		if (error) {
> +		error = bdev_dax_supported(sb, mp->m_ddev_targp->bt_bdev,
> +				sb->s_blocksize);
> +		if (mp->m_rtdev_targp)
> +			error2 = bdev_dax_supported(sb,
> +					mp->m_rtdev_targp->bt_bdev,
> +					sb->s_blocksize);
> +		if (error && error2) {
>  			xfs_alert(mp,
>  			"DAX unsupported by block device. Turning off DAX.");
>  			mp->m_flags &= ~XFS_MOUNT_DAX;
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 5258346..1107a98 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -40,10 +40,11 @@ static inline void put_dax(struct dax_device *dax_dev)
>  
>  int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
>  #if IS_ENABLED(CONFIG_FS_DAX)
> -int __bdev_dax_supported(struct super_block *sb, int blocksize);
> -static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
> +int bdev_dax_supported(struct super_block *sb, struct block_device *bdev,
> +		       int blocksize);
> +static inline int sb_dax_supported(struct super_block *sb, int blocksize)
>  {
> -	return __bdev_dax_supported(sb, blocksize);
> +	return bdev_dax_supported(sb, sb->s_bdev, blocksize);
>  }
>  
>  static inline struct dax_device *fs_dax_get_by_host(const char *host)
> @@ -58,7 +59,14 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
>  
>  struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
>  #else
> -static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
> +static inline int bdev_dax_supported(struct super_block *sb,
> +				     struct block_device *bdev,
> +				     int blocksize)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline int sb_dax_supported(struct super_block *sb, int blocksize)
>  {
>  	return -EOPNOTSUPP;
>  }
> 

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