Re: [PATCH v2 13/14] fs: xfs: Validate atomic writes

John Garry
2024-03-07T10:19:48Z

On 06/03/2024 21:22, Dave Chinner wrote:
> On Mon, Mar 04, 2024 at 01:04:27PM +0000, John Garry wrote:
>> Validate that an atomic write adheres to length/offset rules. Since we
>> require extent alignment for atomic writes, this effectively also enforces
>> that the BIO which iomap produces is aligned.
>>
>> Signed-off-by: John Garry<john.g.garry@oracle.com>
>> ---
>> fs/xfs/xfs_file.c | 11 ++++++++++-
>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
>> index d0bd9d5f596c..cecc5428fd7c 100644
>> --- a/fs/xfs/xfs_file.c
>> +++ b/fs/xfs/xfs_file.c
>> @@ -709,11 +709,20 @@ xfs_file_dio_write(
>> struct kiocb *iocb,
>> struct iov_iter *from)
>> {
>> - struct xfs_inode *ip = XFS_I(file_inode(iocb->ki_filp));
>> + struct inode *inode = file_inode(iocb->ki_filp);
>> + struct xfs_inode *ip = XFS_I(inode);
>> struct xfs_mount *mp = ip->i_mount;
>> struct xfs_buftarg *target = xfs_inode_buftarg(ip);
>> size_t count = iov_iter_count(from);
>>
>> + if (iocb->ki_flags & IOCB_ATOMIC) {
>> + if (!generic_atomic_write_valid(iocb->ki_pos, from,
>> + i_blocksize(inode),
> a.k.a. mp->m_bsize. If you use that here, then the need for the VFS
> inode goes away, too.

ok

>
>> + XFS_FSB_TO_B(mp, xfs_get_extsz(ip)))) {
>> + return -EINVAL;
>> + }
>> + }
> Also, I think the checks are the wrong way around here. We can only
> do IOCB_ATOMIC IO on force aligned/atomic write inodes, so shouldn't
> we be checking that first,

We are checking that, but not here.

In 14/14, we only set FMODE_CAN_ATOMIC_WRITE for when
xfs_inode_has_atomicwrites() is true, and only when
FMODE_CAN_ATOMIC_WRITE is set can we get this far.

I don't see a point in duplicating this xfs_inode_has_atomicwrites()
check, so I will make the commit message clearer on this - ok? Or add a
comment.

> then basing the rest of the checks on the
> assumption that atomic writes are allowed and have been set up
> correctly on the inode? i.e.
>
> if (iocb->ki_flags & IOCB_ATOMIC) {
> if (!xfs_inode_has_atomicwrites(ip))
> return -EINVAL;
> if (!generic_atomic_write_valid(iocb->ki_pos, from,
> mp->m_bsize, ip->i_extsize))
> return -EINVAL;
> }
>
> because xfs_inode_has_atomicwrites() implies ip->i_extsize has been
> set to the required atomic IO size?

I was not too comfortable using ip->i_extsize, as this can be set
without forcealign being set. I know that we would not get this far
without forcealign (being set).

Having said that, I don't like all the xfs_get_extsz() calls, so
something better is required. Let me know you you think.

Thanks,
John