Re: [PATCH for-goldwyn] btrfs: disallow MAP_SYNC outside of DAX mounts

Even if allocation is done synchronously, data would be lost except on actual pmem. Explicit msync()s don't need MAP_SYNC, and don't require a sync per page. Signed-off-by: Adam Borowski <kilobyte(a)angband.pl&gt; --- MAP_SYNC can't be allowed unconditionally, as cacheline flushes don't help guarantee persistency in page cache. This fixes an error in my earlier patch "btrfs: allow MAP_SYNC mmap" -- you'd probably want to amend that. fs/btrfs/file.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 362a9cf9dcb2..0bc5428037ba 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2233,6 +2233,13 @@ static int btrfs_file_mmap(struct file *filp, struct vm_area_struct *vma) if (!IS_DAX(inode) && !mapping->a_ops->readpage) return -ENOEXEC; + /* + * Normal operation of btrfs is pretty much an antithesis of MAP_SYNC; + * supporting it outside DAX is pointless. + */ + if (!IS_DAX(inode) && (vma->vm_flags & VM_SYNC)) + return -EOPNOTSUPP; +