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check_for_nsfs_mounts(): no need to take locks

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Currently we are taking mount_writer; what that function needs is
either mount_locked_reader (we are not changing anything, we just
want to iterate through the subtree) or namespace_shared and
a reference held by caller on the root of subtree - that's also
enough to stabilize the topology.

The thing is, all callers are already holding at least namespace_shared
as well as a reference to the root of subtree.

Let's make the callers provide locking warranties - don't mess with
mount_lock in check_for_nsfs_mounts() itself and document the locking
requirements.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2025-08-20 20:28:35 -04:00
parent 747e91e5b7
commit 6b448d7a7c
1 changed files with 5 additions and 11 deletions
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16
fs/namespace.c
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@@ -2402,21 +2402,15 @@ bool has_locked_children(struct mount *mnt, struct dentry *dentry)
* specified subtree. Such references can act as pins for mount namespaces
* that aren't checked by the mount-cycle checking code, thereby allowing
* cycles to be made.
*
* locks: mount_locked_reader || namespace_shared && pinned(subtree)
*/
static bool check_for_nsfs_mounts(struct mount *subtree)
{
struct mount *p;
bool ret = false;
lock_mount_hash();
for (p = subtree; p; p = next_mnt(p, subtree))
for (struct mount *p = subtree; p; p = next_mnt(p, subtree))
if (mnt_ns_loop(p->mnt.mnt_root))
goto out;
ret = true;
out:
unlock_mount_hash();
return ret;
return false;
return true;
}
/**