Message-ID: <a2a0ec49-37e5-4e0f-9916-d9d05cf5bb96@oracle.com>
Date: Thu, 22 Aug 2024 18:45:16 +0100
From: John Garry <john.g.garry@...cle.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: axboe@...nel.dk, brauner@...nel.org, viro@...iv.linux.org.uk, jack@...e.cz,
        chandan.babu@...cle.com, dchinner@...hat.com, hch@....de,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, hare@...e.de,
        martin.petersen@...cle.com, catherine.hoang@...cle.com,
        kbusch@...nel.org
Subject: Re: [PATCH v5 4/7] xfs: Support FS_XFLAG_ATOMICWRITES for forcealign

On 21/08/2024 18:07, Darrick J. Wong wrote:
> On Sat, Aug 17, 2024 at 09:47:57AM +0000, John Garry wrote:
>> Add initial support for new flag FS_XFLAG_ATOMICWRITES for forcealign
>> enabled.
>>
>> This flag is a file attribute that mirrors an ondisk inode flag.  Actual
>> support for untorn file writes (for now) depends on both the iflag and the
>> underlying storage devices, which we can only really check at statx and
>> pwritev2() time.  This is the same story as FS_XFLAG_DAX, which signals to
>> the fs that we should try to enable the fsdax IO path on the file (instead
>> of the regular page cache), but applications have to query STAT_ATTR_DAX to
>> find out if they really got that IO path.
>>
>> Current kernel support for atomic writes is based on HW support (for atomic
>> writes). As such, it is required to ensure extent alignment with
>> atomic_write_unit_max so that an atomic write can result in a single
>> HW-compliant IO operation.
>>
>> rtvol also guarantees extent alignment, but we are basing support initially
>> on forcealign, which is not supported for rtvol yet.
>>
>> Signed-off-by: John Garry <john.g.garry@...cle.com>
>> ---
>>   fs/xfs/libxfs/xfs_format.h     | 11 +++++--
>>   fs/xfs/libxfs/xfs_inode_buf.c  | 52 ++++++++++++++++++++++++++++++++++
>>   fs/xfs/libxfs/xfs_inode_util.c |  4 +++
>>   fs/xfs/libxfs/xfs_sb.c         |  2 ++
>>   fs/xfs/xfs_buf.c               | 15 +++++++++-
>>   fs/xfs/xfs_buf.h               |  4 ++-
>>   fs/xfs/xfs_buf_mem.c           |  2 +-
>>   fs/xfs/xfs_inode.h             |  5 ++++
>>   fs/xfs/xfs_ioctl.c             | 52 ++++++++++++++++++++++++++++++++++
>>   fs/xfs/xfs_mount.h             |  2 ++
>>   fs/xfs/xfs_super.c             | 12 ++++++++
>>   include/uapi/linux/fs.h        |  1 +
>>   12 files changed, 157 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
>> index 04c6cbc943c2..a9f3389438a6 100644
>> --- a/fs/xfs/libxfs/xfs_format.h
>> +++ b/fs/xfs/libxfs/xfs_format.h
>> @@ -353,12 +353,16 @@ xfs_sb_has_compat_feature(
>>   #define XFS_SB_FEAT_RO_COMPAT_REFLINK  (1 << 2)		/* reflinked files */
>>   #define XFS_SB_FEAT_RO_COMPAT_INOBTCNT (1 << 3)		/* inobt block counts */
>>   #define XFS_SB_FEAT_RO_COMPAT_FORCEALIGN (1 << 30)	/* aligned file data extents */
>> +#define XFS_SB_FEAT_RO_COMPAT_ATOMICWRITES (1 << 31)	/* atomicwrites enabled */
> 
> Do you ever see test failures in xfs/270?

Well it wasn't with forcealign only. I'll check again for atomic writes.

> 
>> +
>>   #define XFS_SB_FEAT_RO_COMPAT_ALL \
>>   		(XFS_SB_FEAT_RO_COMPAT_FINOBT | \
>>   		 XFS_SB_FEAT_RO_COMPAT_RMAPBT | \
>>   		 XFS_SB_FEAT_RO_COMPAT_REFLINK| \
>>   		 XFS_SB_FEAT_RO_COMPAT_INOBTCNT | \
>> -		 XFS_SB_FEAT_RO_COMPAT_FORCEALIGN)
>> +		 XFS_SB_FEAT_RO_COMPAT_FORCEALIGN | \
>> +		 XFS_SB_FEAT_RO_COMPAT_ATOMICWRITES)
>> +
>>   #define XFS_SB_FEAT_RO_COMPAT_UNKNOWN	~XFS_SB_FEAT_RO_COMPAT_ALL
>>   static inline bool
>>   xfs_sb_has_ro_compat_feature(
>> @@ -1097,6 +1101,7 @@ static inline void xfs_dinode_put_rdev(struct xfs_dinode *dip, xfs_dev_t rdev)
>>   #define XFS_DIFLAG2_NREXT64_BIT 4	/* large extent counters */
>>   /* data extent mappings for regular files must be aligned to extent size hint */
>>   #define XFS_DIFLAG2_FORCEALIGN_BIT 5
>> +#define XFS_DIFLAG2_ATOMICWRITES_BIT 6
>>   
>>   #define XFS_DIFLAG2_DAX		(1 << XFS_DIFLAG2_DAX_BIT)
>>   #define XFS_DIFLAG2_REFLINK     (1 << XFS_DIFLAG2_REFLINK_BIT)
>> @@ -1104,10 +1109,12 @@ static inline void xfs_dinode_put_rdev(struct xfs_dinode *dip, xfs_dev_t rdev)
>>   #define XFS_DIFLAG2_BIGTIME	(1 << XFS_DIFLAG2_BIGTIME_BIT)
>>   #define XFS_DIFLAG2_NREXT64	(1 << XFS_DIFLAG2_NREXT64_BIT)
>>   #define XFS_DIFLAG2_FORCEALIGN	(1 << XFS_DIFLAG2_FORCEALIGN_BIT)
>> +#define XFS_DIFLAG2_ATOMICWRITES	(1 << XFS_DIFLAG2_ATOMICWRITES_BIT)
>>   
>>   #define XFS_DIFLAG2_ANY \
>>   	(XFS_DIFLAG2_DAX | XFS_DIFLAG2_REFLINK | XFS_DIFLAG2_COWEXTSIZE | \
>> -	 XFS_DIFLAG2_BIGTIME | XFS_DIFLAG2_NREXT64 | XFS_DIFLAG2_FORCEALIGN)
>> +	 XFS_DIFLAG2_BIGTIME | XFS_DIFLAG2_NREXT64 | XFS_DIFLAG2_FORCEALIGN | \
>> +	 XFS_DIFLAG2_ATOMICWRITES)
>>   
>>   static inline bool xfs_dinode_has_bigtime(const struct xfs_dinode *dip)
>>   {
>> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
>> index 1c59891fa9e2..59933c7df56d 100644
>> --- a/fs/xfs/libxfs/xfs_inode_buf.c
>> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
>> @@ -178,7 +178,10 @@ xfs_inode_from_disk(
>>   	struct xfs_inode	*ip,
>>   	struct xfs_dinode	*from)
>>   {
>> +	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
>>   	struct inode		*inode = VFS_I(ip);
>> +	struct xfs_mount	*mp = ip->i_mount;
>> +	struct xfs_sb		*sbp = &mp->m_sb;
>>   	int			error;
>>   	xfs_failaddr_t		fa;
>>   
>> @@ -261,6 +264,13 @@ xfs_inode_from_disk(
>>   	}
>>   	if (xfs_is_reflink_inode(ip))
>>   		xfs_ifork_init_cow(ip);
>> +
>> +	if (xfs_inode_has_atomicwrites(ip)) {
>> +		if (sbp->sb_blocksize < target->bt_bdev_awu_min ||
>> +		    sbp->sb_blocksize * ip->i_extsize > target->bt_bdev_awu_max)
> 
> Can this multiplication trigger integer overflows?

I should just use xfs_inode_alloc_unitsize()

> 
>> +			ip->i_diflags2 &= ~XFS_DIFLAG2_ATOMICWRITES;
> 
> Ondisk iflag updates must use transactions.

I want to change this.

The idea was to runtime clear this flag in case the bdev cannot satisfy 
the FS atomic write range, but that does not work.

> 
> Or you can fail IOCB_ATOMIC writes if XFS_DIFLAG2_ATOMICWRITES is set
> but the forcealign blocksize doesn't fit with awu_min/max.

I'd rather just not set FMODE_CAN_ATOMIC_WRITE

> 
>> +	}
>> +
>>   	return 0;
>>   
>>   out_destroy_data_fork:
>> @@ -483,6 +493,40 @@ xfs_dinode_verify_nrext64(
>>   	return NULL;
>>   }
>>   
>> +static xfs_failaddr_t
>> +xfs_inode_validate_atomicwrites(
>> +	struct xfs_mount	*mp,
>> +	uint32_t		extsize,
>> +	uint64_t		flags2)
>> +{
>> +	/* superblock rocompat feature flag */
>> +	if (!xfs_has_atomicwrites(mp))
>> +		return __this_address;
>> +
>> +	/*
>> +	 * forcealign is required, so rely on sanity checks in
>> +	 * xfs_inode_validate_forcealign()
>> +	 */
>> +	if (!(flags2 & XFS_DIFLAG2_FORCEALIGN))
>> +		return __this_address;
>> +
>> +	if (!is_power_of_2(extsize))
>> +		return __this_address;
>> +
>> +	/* Required to guarantee data block alignment */
>> +	if (mp->m_sb.sb_agblocks % extsize)
>> +		return __this_address;
>> +
>> +	/* Requires stripe unit+width be a multiple of extsize */
>> +	if (mp->m_dalign && (mp->m_dalign % extsize))
>> +		return __this_address;
>> +
>> +	if (mp->m_swidth && (mp->m_swidth % extsize))
> 
> IIRC m_dalign and m_swidth can be set at mount time,

I thought that these were fixed at mkfs time, however I see that the 
comment for xfs_update_alignment() mentions "values based on mount 
options". And we are reading mp values, and not sbp values, which is a 
good clue...

> which can result in
> inode verifiers logging corruption errors if those parameters change.  I
> think we should validate these two congruencies when setting
> FMODE_CAN_ATOMIC_WRITE.

That would make sense.

> 
>> +		return __this_address;
>> +
>> +	return NULL;
>> +}
>> +
>>   xfs_failaddr_t
>>   xfs_dinode_verify(
>>   	struct xfs_mount	*mp,
>> @@ -666,6 +710,14 @@ xfs_dinode_verify(
>>   			return fa;
>>   	}
>>   
>> +	if (flags2 & XFS_DIFLAG2_ATOMICWRITES) {
>> +		fa = xfs_inode_validate_atomicwrites(mp,
>> +				be32_to_cpu(dip->di_extsize),
>> +				flags2);
>> +		if (fa)
>> +			return fa;
>> +	}
>> +
>>   	return NULL;
>>   }
>>   
>> diff --git a/fs/xfs/libxfs/xfs_inode_util.c b/fs/xfs/libxfs/xfs_inode_util.c
>> index b264939d8855..dbd5b16e1844 100644
>> --- a/fs/xfs/libxfs/xfs_inode_util.c
>> +++ b/fs/xfs/libxfs/xfs_inode_util.c
>> @@ -82,6 +82,8 @@ xfs_flags2diflags2(
>>   		di_flags2 |= XFS_DIFLAG2_COWEXTSIZE;
>>   	if (xflags & FS_XFLAG_FORCEALIGN)
>>   		di_flags2 |= XFS_DIFLAG2_FORCEALIGN;
>> +	if (xflags & FS_XFLAG_ATOMICWRITES)
>> +		di_flags2 |= XFS_DIFLAG2_ATOMICWRITES;
>>   
>>   	return di_flags2;
>>   }
>> @@ -130,6 +132,8 @@ xfs_ip2xflags(
>>   			flags |= FS_XFLAG_COWEXTSIZE;
>>   		if (ip->i_diflags2 & XFS_DIFLAG2_FORCEALIGN)
>>   			flags |= FS_XFLAG_FORCEALIGN;
>> +		if (ip->i_diflags2 & XFS_DIFLAG2_ATOMICWRITES)
>> +			flags |= FS_XFLAG_ATOMICWRITES;
>>   	}
>>   
>>   	if (xfs_inode_has_attr_fork(ip))
>> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
>> index e56911553edd..5de8725bf93a 100644
>> --- a/fs/xfs/libxfs/xfs_sb.c
>> +++ b/fs/xfs/libxfs/xfs_sb.c
>> @@ -166,6 +166,8 @@ xfs_sb_version_to_features(
>>   		features |= XFS_FEAT_INOBTCNT;
>>   	if (sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_FORCEALIGN)
>>   		features |= XFS_FEAT_FORCEALIGN;
>> +	if (sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_ATOMICWRITES)
>> +		features |= XFS_FEAT_ATOMICWRITES;
>>   	if (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_FTYPE)
>>   		features |= XFS_FEAT_FTYPE;
>>   	if (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_SPINODES)
>> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
>> index aa4dbda7b536..44bee3e2b2bb 100644
>> --- a/fs/xfs/xfs_buf.c
>> +++ b/fs/xfs/xfs_buf.c
>> @@ -2060,6 +2060,8 @@ int
>>   xfs_init_buftarg(
>>   	struct xfs_buftarg		*btp,
>>   	size_t				logical_sectorsize,
>> +	unsigned int			awu_min,
>> +	unsigned int			awu_max,
>>   	const char			*descr)
>>   {
>>   	/* Set up device logical sector size mask */
>> @@ -2086,6 +2088,9 @@ xfs_init_buftarg(
>>   	btp->bt_shrinker->scan_objects = xfs_buftarg_shrink_scan;
>>   	btp->bt_shrinker->private_data = btp;
>>   	shrinker_register(btp->bt_shrinker);
>> +
>> +	btp->bt_bdev_awu_min = awu_min;
>> +	btp->bt_bdev_awu_max = awu_max;
>>   	return 0;
>>   
>>   out_destroy_io_count:
>> @@ -2102,6 +2107,7 @@ xfs_alloc_buftarg(
>>   {
>>   	struct xfs_buftarg	*btp;
>>   	const struct dax_holder_operations *ops = NULL;
>> +	unsigned int awu_min = 0, awu_max = 0;
>>   
>>   #if defined(CONFIG_FS_DAX) && defined(CONFIG_MEMORY_FAILURE)
>>   	ops = &xfs_dax_holder_operations;
>> @@ -2115,6 +2121,13 @@ xfs_alloc_buftarg(
>>   	btp->bt_daxdev = fs_dax_get_by_bdev(btp->bt_bdev, &btp->bt_dax_part_off,
>>   					    mp, ops);
>>   
>> +	if (bdev_can_atomic_write(btp->bt_bdev)) {
>> +		struct request_queue *q = bdev_get_queue(btp->bt_bdev);
>> +
>> +		awu_min = queue_atomic_write_unit_min_bytes(q);
>> +		awu_max = queue_atomic_write_unit_max_bytes(q);
>> +	}
>> +
>>   	/*
>>   	 * When allocating the buftargs we have not yet read the super block and
>>   	 * thus don't know the file system sector size yet.
>> @@ -2122,7 +2135,7 @@ xfs_alloc_buftarg(
>>   	if (xfs_setsize_buftarg(btp, bdev_logical_block_size(btp->bt_bdev)))
>>   		goto error_free;
>>   	if (xfs_init_buftarg(btp, bdev_logical_block_size(btp->bt_bdev),
>> -			mp->m_super->s_id))
>> +			awu_min, awu_max, mp->m_super->s_id))
>>   		goto error_free;
>>   
>>   	return btp;
>> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
>> index b1580644501f..3bcd8137d739 100644
>> --- a/fs/xfs/xfs_buf.h
>> +++ b/fs/xfs/xfs_buf.h
>> @@ -124,6 +124,8 @@ struct xfs_buftarg {
>>   	struct percpu_counter	bt_io_count;
>>   	struct ratelimit_state	bt_ioerror_rl;
>>   
>> +	unsigned int		bt_bdev_awu_min, bt_bdev_awu_max;
> 
> Please add a comment here about what these mean.  Not everyone is going
> to know what "awu" abbreviates.

sure

>> +
>>   static int
>>   xfs_ioctl_setattr_xflags(
>>   	struct xfs_trans	*tp,
>> @@ -511,9 +554,12 @@ xfs_ioctl_setattr_xflags(
>>   	struct xfs_mount	*mp = ip->i_mount;
>>   	bool			rtflag = (fa->fsx_xflags & FS_XFLAG_REALTIME);
>>   	bool			forcealign = fa->fsx_xflags & FS_XFLAG_FORCEALIGN;
>> +	bool			atomic_writes;
>>   	uint64_t		i_flags2;
>>   	int			error;
>>   
>> +	atomic_writes = fa->fsx_xflags & FS_XFLAG_ATOMICWRITES;
>> +
>>   	/* Can't change RT or forcealign flags if any extents are allocated. */
>>   	if (rtflag != XFS_IS_REALTIME_INODE(ip) ||
>>   	    forcealign != xfs_inode_has_forcealign(ip)) {
>> @@ -554,6 +600,12 @@ xfs_ioctl_setattr_xflags(
>>   			return error;
>>   	}
>>   
>> +	if (atomic_writes) {
>> +		error = xfs_ioctl_setattr_atomicwrites(ip, fa);
>> +		if (error)
>> +			return error;
>> +	}
>> +
>>   	ip->i_diflags = xfs_flags2diflags(ip, fa->fsx_xflags);
>>   	ip->i_diflags2 = i_flags2;
>>   
>> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
>> index 30228fea908d..0c5a3ae3cdaf 100644
>> --- a/fs/xfs/xfs_mount.h
>> +++ b/fs/xfs/xfs_mount.h
>> @@ -300,6 +300,7 @@ typedef struct xfs_mount {
>>   #define XFS_FEAT_NREXT64	(1ULL << 26)	/* large extent counters */
>>   #define XFS_FEAT_EXCHANGE_RANGE	(1ULL << 27)	/* exchange range */
>>   #define XFS_FEAT_FORCEALIGN	(1ULL << 28)	/* aligned file data extents */
>> +#define XFS_FEAT_ATOMICWRITES	(1ULL << 29)	/* atomic writes support */
>>   
>>   /* Mount features */
>>   #define XFS_FEAT_NOATTR2	(1ULL << 48)	/* disable attr2 creation */
>> @@ -387,6 +388,7 @@ __XFS_HAS_V4_FEAT(v3inodes, V3INODES)
>>   __XFS_HAS_V4_FEAT(crc, CRC)
>>   __XFS_HAS_V4_FEAT(pquotino, PQUOTINO)
>>   __XFS_HAS_FEAT(forcealign, FORCEALIGN)
>> +__XFS_HAS_FEAT(atomicwrites, ATOMICWRITES)
>>   
>>   /*
>>    * Mount features
>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
>> index b52a01b50387..5352b90b2bb6 100644
>> --- a/fs/xfs/xfs_super.c
>> +++ b/fs/xfs/xfs_super.c
>> @@ -1721,6 +1721,18 @@ xfs_fs_fill_super(
>>   		mp->m_features &= ~XFS_FEAT_DISCARD;
>>   	}
>>   
>> +	if (xfs_has_atomicwrites(mp)) {
>> +		if (!xfs_has_forcealign(mp)) {
>> +			xfs_alert(mp,
>> +	"forcealign required for atomicwrites!");
> 
> This (atomicwrites && !forcealign) ought to be checked in the superblock
> verifier.

You mean in xfs_fs_validate_params(), right?

Thanks,
John

> 

Powered by blists - more mailing lists