Commit 1ea806165ec5 for kernel

commit 1ea806165ec5fb8bca5d9990392fdb4f53a97977
Author: Sasha Levin <sashal@kernel.org>
Date:   Mon Oct 26 11:26:50 2026 -0400

    fuse: fix link error with CONFIG_FUSE_PASSTHROUGH=n

    Commit 2f19d54c055d ("fuse: support 64 bit, server allocated backing ID")
    moved the CONFIG_FUSE_PASSTHROUGH check out of the backing ioctl handlers
    and into fuse_get_conn_for_passthrough(). The calls from the handlers
    into backing.c, which is only built with CONFIG_FUSE_PASSTHROUGH, are now
    only removed if the compiler inlines that helper. It does not have to,
    and with gcc 11 and CONFIG_CC_OPTIMIZE_FOR_SIZE it doesn't:

      dev.c:(.text+0x355c): undefined reference to `fuse_backing_open'
      nios2-linux-ld: dev.c:(.text+0x3594): undefined reference to `fuse_backing_open_64'
      nios2-linux-ld: dev.c:(.text+0x35d0): undefined reference to `fuse_backing_close'

    Check CONFIG_FUSE_PASSTHROUGH in each handler again, as
    fuse_notify_backing_remove() does. The check still comes after the
    fuse_get_dev() and -ENOTCONN checks, so the errors userspace sees do not
    change.

    Fixes: 2f19d54c055d ("fuse: support 64 bit, server allocated backing ID")
    Reported-by: kernel test robot <lkp@intel.com>
    Closes: https://lore.kernel.org/oe-kbuild-all/202610171310.uqRzJkIx-lkp@intel.com/
    Closes: https://lore.kernel.org/oe-kbuild-all/202610260719.sj08mXBr-lkp@intel.com/
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1a40b60afb98..3641abb90d6b 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2334,9 +2334,6 @@ static struct fuse_conn *fuse_get_conn_for_passthrough(struct file *file)
 	if (!smp_load_acquire(&fud->chan->initialized))
 		return ERR_PTR(-ENOTCONN);

-	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
-		return ERR_PTR(-EOPNOTSUPP);
-
 	return fud->chan->conn;
 }

@@ -2349,6 +2346,9 @@ static long fuse_dev_ioctl_backing_open(struct file *file,
 	if (IS_ERR(fc))
 		return PTR_ERR(fc);

+	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+		return -EOPNOTSUPP;
+
 	if (copy_from_user(&map, argp, sizeof(map)))
 		return -EFAULT;

@@ -2364,6 +2364,9 @@ static long fuse_dev_ioctl_backing_create(struct file *file,
 	if (IS_ERR(fc))
 		return PTR_ERR(fc);

+	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+		return -EOPNOTSUPP;
+
 	if (copy_from_user(&map, argp, sizeof(map)))
 		return -EFAULT;

@@ -2378,6 +2381,9 @@ static long fuse_dev_ioctl_backing_close(struct file *file, __u32 __user *argp)
 	if (IS_ERR(fc))
 		return PTR_ERR(fc);

+	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+		return -EOPNOTSUPP;
+
 	if (get_user(backing_id, argp))
 		return -EFAULT;