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>
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
@@ -2233,6 +2233,13 @@ static int btrfs_file_mmap(struct file *filp, struct vm_area_struct
if (!IS_DAX(inode) && !mapping->a_ops->readpage)
+ * 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;
vma->vm_ops = &btrfs_dax_vm_ops;