Re: [PATCH v9 13/14] xfs: don't enable DAX on zoned inodes

[sashiko-bot@kernel.org]

> A store through a shared mapping can dereference a NULL pointer if the
> file is zoned and has S_DAX.
> 
> The zoned code does not support DAX, but XFS doesn't check for this:
> with dax=always or FS_XFLAG_DAX, an inode gets S_DAX if its device does
> DAX, and an internal zoned section on pmem does. The write fault then
> takes the zoned path:
> 
>     xfs_filemap_fault()
>       xfs_write_fault()
>         xfs_write_fault_zoned()
>           page_folio(vmf->page)     /* NULL in a DAX fault */
> 
> ftruncate() crashes in a similar way, in xfs_reflink_end_cow().
> 
> The fix used here is to never set S_DAX on a zoned inode, and to refuse
> to change the realtime flag of an S_DAX inode on a zoned file system.
> 
> Zoned files now use the page cache with dax=always or FS_XFLAG_DAX. A
> file whose realtime flag is cleared stays without DAX until its inode
> is evicted.
> 
> Fixes: be458049ffe3 ("xfs: enable the zoned RT device feature")
> Signed-off-by: Chris Mason <mason@kernel.org>

Sashiko has reviewed this patch and found no issues.

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