[PATCH RFC v3 16/26] pnfs/blocklayout: use scoped_with_init_fs() for SCSI device lookup

Christian Brauner
2026-03-11T21:56:51Z

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.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/nfs/blocklayout/dev.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/blocklayout/dev.c b/fs/nfs/blocklayout/dev.c
index cc6327d97a91..eed960839608 100644
--- a/fs/nfs/blocklayout/dev.c
+++ b/fs/nfs/blocklayout/dev.c
@@ -4,6 +4,7 @@
*/
#include <linux/sunrpc/svc.h>
#include <linux/blkdev.h>
+#include <linux/fs_struct.h>
#include <linux/nfs4.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_xdr.h>
@@ -363,21 +364,27 @@ static struct file *
bl_open_path(struct pnfs_block_volume *v, const char *prefix)
{
struct file *bdev_file;
- const char *devname;
+ const char *devname __free(kfree) = NULL;

devname = kasprintf(GFP_KERNEL, "/dev/disk/by-id/%s%*phN",
prefix, v->scsi.designator_len, v->scsi.designator);
if (!devname)
return ERR_PTR(-ENOMEM);

- bdev_file = bdev_file_open_by_path(devname, BLK_OPEN_READ | BLK_OPEN_WRITE,
+ if (tsk_is_kthread(current)) {
+ scoped_with_init_fs()
+ bdev_file = bdev_file_open_by_path(devname,
+ BLK_OPEN_READ | BLK_OPEN_WRITE,
NULL, NULL);
+ } else {
+ bdev_file = bdev_file_open_by_path(devname,
+ BLK_OPEN_READ | BLK_OPEN_WRITE, NULL, NULL);
+ }
if (IS_ERR(bdev_file)) {
dprintk("failed to open device %s (%ld)\n",
devname, PTR_ERR(bdev_file));
}

- kfree(devname);
return bdev_file;
}

--
2.47.3