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pnfs/blocklayout: use scoped_with_init_fs() for SCSI device lookup

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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>
This commit is contained in:
Christian Brauner
2026-06-01 15:56:49 +02:00
parent c95396ec55
commit ba2e078299
1 changed files with 11 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
fs/nfs/blocklayout/dev.c
View File

@@ -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>
@@ -363,15 +364,22 @@ 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, NULL, NULL);
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));
@@ -380,7 +388,6 @@ bl_open_path(struct pnfs_block_volume *v, const char *prefix)
file_bdev(bdev_file)->bd_disk->disk_name);
}
kfree(devname);
return bdev_file;
}