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finish_automount(): take the lock_mount() analogue into a helper

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finish_automount() can't use lock_mount() - it treats finding something
already mounted as "quitely drop our mount and return 0", not as
"mount on top of whatever mounted there".  It's been open-coded;
let's take it into a helper similar to lock_mount().  "something's
already mounted" => -EBUSY, finish_automount() needs to distinguish
it from the normal case and it can't happen in other failure cases.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2025-08-22 12:59:10 -04:00
parent 6bbbc4a04a
commit 9bf5d48852
1 changed files with 25 additions and 17 deletions
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42
fs/namespace.c
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@@ -3781,9 +3781,29 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
return err;
}
int finish_automount(struct vfsmount *m, const struct path *path)
static int lock_mount_exact(const struct path *path,
struct pinned_mountpoint *mp)
{
struct dentry *dentry = path->dentry;
int err;
inode_lock(dentry->d_inode);
namespace_lock();
if (unlikely(cant_mount(dentry)))
err = -ENOENT;
else if (path_overmounted(path))
err = -EBUSY;
else
err = get_mountpoint(dentry, mp);
if (unlikely(err)) {
namespace_unlock();
inode_unlock(dentry->d_inode);
}
return err;
}
int finish_automount(struct vfsmount *m, const struct path *path)
{
struct pinned_mountpoint mp = {};
struct mount *mnt;
int err;
@@ -3805,20 +3825,11 @@ int finish_automount(struct vfsmount *m, const struct path *path)
* that overmounts our mountpoint to be means "quitely drop what we've
* got", not "try to mount it on top".
*/
inode_lock(dentry->d_inode);
namespace_lock();
if (unlikely(cant_mount(dentry))) {
err = -ENOENT;
goto discard_locked;
err = lock_mount_exact(path, &mp);
if (unlikely(err)) {
mntput(m);
return err == -EBUSY ? 0 : err;
}
if (path_overmounted(path)) {
err = 0;
goto discard_locked;
}
err = get_mountpoint(dentry, &mp);
if (err)
goto discard_locked;
err = do_add_mount(mnt, mp.mp, path,
path->mnt->mnt_flags | MNT_SHRINKABLE);
unlock_mount(&mp);
@@ -3826,9 +3837,6 @@ int finish_automount(struct vfsmount *m, const struct path *path)
goto discard;
return 0;
discard_locked:
namespace_unlock();
inode_unlock(dentry->d_inode);
discard:
mntput(m);
return err;