Re: [PATCH v6 12/15] xfs: require mmap lock for xfs_break_layouts()

Dan Williams
2018-03-16T19:10:09Z

On Fri, Mar 16, 2018 at 12:04 PM, Christoph Hellwig <hch@lst.de> wrote:
> On Thu, Mar 15, 2018 at 08:52:29AM -0700, Dan Williams wrote:
>> In preparation for adding coordination between truncate operations and
>> busy dax-pages, extend xfs_break_layouts() to assume it must be called
>> with the mmap lock held. This locking scheme will be required for
>> coordinating the break of 'dax layouts' (non-idle dax (ZONE_DEVICE)
>> pages mapped into the file's address space).
>
> This requirement wasn't really there in the last series, why do we
> require it now?

It seems I misinterpreted your feedback.

>
> As far as I can tell all we'd need is to just drop this assert:
>
>> - ASSERT(xfs_isilocked(ip, XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL));
>> + ASSERT(xfs_isilocked(ip, XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL
>> + | XFS_MMAPLOCK_EXCL));
>
> entirely.
>
>> while ((error = break_layout(inode, false) == -EWOULDBLOCK)) {
>> xfs_iunlock(ip, *iolock);
>> error = break_layout(inode, true);
>> - *iolock = XFS_IOLOCK_EXCL;
>> + *iolock &= ~XFS_IOLOCK_SHARED;
>> + *iolock |= XFS_IOLOCK_EXCL;
>> xfs_ilock(ip, *iolock);
>
> And take this one hunk from your patch.
>
> To enable the DAX use case.

Yeah, that looks good to me.