bl_open_path() resolves pNFS block device paths under /dev/disk/by-id/
via bdev_file_open_by_path() -> lookup_bdev() -> kern_path(). This
path resolution uses current->fs->root.
With kthreads now starting in nullfs, this fails when the call
originates from writeback kworker context because current->fs->root
points at the empty nullfs. The full callchain from kworker is:
wb_workfn [kworker writeback callback]
...
nfs_writepages [address_space_operations.writepages]
nfs_do_writepage
nfs_pageio_add_request
...
bl_pg_init_write [nfs_pageio_ops.pg_init]
pnfs_generic_pg_init_write
pnfs_update_layout
nfs4_proc_layoutget [synchronous RPC]
pnfs_layout_process
bl_alloc_lseg
bl_alloc_extent
bl_find_get_deviceid
bl_alloc_deviceid_node
bl_parse_deviceid
bl_parse_scsi
bl_open_path
bdev_file_open_by_path
lookup_bdev
kern_path <- current->fs->root
bl_open_path() can also be reached from userspace process context (e.g.
open, read, write syscalls via pnfs_update_layout). In that case
current->fs must not be overridden as the path should resolve against
the calling process's filesystem root.
Add a tsk_is_kthread() conditional in bl_open_path() to only apply
scoped_with_init_fs() in kthread context.
Link: https://patch.msgid.link/20260601-work-kthread-nullfs-v4-16-77ee053060e0@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
ba2e078299