From 68456d05eb57a5d16b4be2d3caf421bdcf2de72e Mon Sep 17 00:00:00 2001 From: John Garry Date: Thu, 24 Jul 2025 08:12:14 +0000 Subject: [PATCH] xfs: disallow atomic writes on DAX Atomic writes are not currently supported for DAX, but two problems exist: - we may go down DAX write path for IOCB_ATOMIC, which does not handle IOCB_ATOMIC properly - we report non-zero atomic write limits in statx (for DAX inodes) We may want atomic writes support on DAX in future, but just disallow for now. For this, ensure when IOCB_ATOMIC is set that we check the write size versus the atomic write min and max before branching off to the DAX write path. This is not strictly required for DAX, as we should not get this far in the write path as FMODE_CAN_ATOMIC_WRITE should not be set. In addition, due to reflink being supported for DAX, we automatically get CoW-based atomic writes support being advertised. Remedy this by disallowing atomic writes for a DAX inode for both sw and hw modes. Reported-by: Darrick J. Wong Fixes: 9dffc58f2384 ("xfs: update atomic write limits") Reviewed-by: Darrick J. Wong Signed-off-by: John Garry Signed-off-by: Carlos Maiolino --- fs/xfs/xfs_file.c | 6 +++--- fs/xfs/xfs_inode.h | 11 +++++++++++ fs/xfs/xfs_iops.c | 5 +++-- 3 files changed, 17 insertions(+), 5 deletions(-) diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 55a304cb3aef4..f96fbf5c54c99 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -1101,9 +1101,6 @@ xfs_file_write_iter( if (xfs_is_shutdown(ip->i_mount)) return -EIO; - if (IS_DAX(inode)) - return xfs_file_dax_write(iocb, from); - if (iocb->ki_flags & IOCB_ATOMIC) { if (ocount < xfs_get_atomic_write_min(ip)) return -EINVAL; @@ -1116,6 +1113,9 @@ xfs_file_write_iter( return ret; } + if (IS_DAX(inode)) + return xfs_file_dax_write(iocb, from); + if (iocb->ki_flags & IOCB_DIRECT) { /* * Allow a directio write to fall back to a buffered diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h index 07fbdcc4cbf58..bd6d335571943 100644 --- a/fs/xfs/xfs_inode.h +++ b/fs/xfs/xfs_inode.h @@ -358,9 +358,20 @@ static inline bool xfs_inode_has_bigrtalloc(const struct xfs_inode *ip) static inline bool xfs_inode_can_hw_atomic_write(const struct xfs_inode *ip) { + if (IS_DAX(VFS_IC(ip))) + return false; + return xfs_inode_buftarg(ip)->bt_awu_max > 0; } +static inline bool xfs_inode_can_sw_atomic_write(const struct xfs_inode *ip) +{ + if (IS_DAX(VFS_IC(ip))) + return false; + + return xfs_can_sw_atomic_write(ip->i_mount); +} + /* * In-core inode flags. */ diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c index 149b5460fbfd8..603effabe1ee1 100644 --- a/fs/xfs/xfs_iops.c +++ b/fs/xfs/xfs_iops.c @@ -616,7 +616,8 @@ xfs_get_atomic_write_min( * write of exactly one single fsblock if the bdev will make that * guarantee for us. */ - if (xfs_inode_can_hw_atomic_write(ip) || xfs_can_sw_atomic_write(mp)) + if (xfs_inode_can_hw_atomic_write(ip) || + xfs_inode_can_sw_atomic_write(ip)) return mp->m_sb.sb_blocksize; return 0; @@ -633,7 +634,7 @@ xfs_get_atomic_write_max( * write of exactly one single fsblock if the bdev will make that * guarantee for us. */ - if (!xfs_can_sw_atomic_write(mp)) { + if (!xfs_inode_can_sw_atomic_write(ip)) { if (xfs_inode_can_hw_atomic_write(ip)) return mp->m_sb.sb_blocksize; return 0; -- 2.51.0