It seems that a process blocked in a write to an xfs filesystem due to
xfs_freeze cannot be frozen by the freezer.
I see this if I suspend my laptop while doing something xfs-filesystem
intensive, like a kernel build. My suspend scripts freeze the XFS
filesystem (as Dave said I should), which presumably blocks some writer,
and then the freezer times out and fails to complete.
Here's part of the process dump the freezer does when it times out:
cc1 D 00000000 0 18138 18137
dd5f1e24 00200082 00000002 00000000 ecdeeb00 ecdeec64 c200f280 00000001
009c09a0 dd5f1e0c dd5f1e0c 0000000f 00000000 00000000 00000000 dd5f1e74
c7beb480 dd5f1e88 dd5f1ea8 c0228d97 e8889540 dd5f1e38 c015b75d dd5f1e44
I haven't looked at how to fix this yet. I only just worked out why I
was getting suspend failures.