Threads are allowed to switch mount namespaces if the filesystem
details aren't being shared. That's the purpose of the check in
the kernel quoted by the comment:
if (fs->users != 1)
return -EINVAL;
It's been this way since the code was originally merged in v3.8.
Signed-off-by: Mike Frysinger <vapier@xxxxxxxxxx>
---
man2/setns.2 | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/man2/setns.2 b/man2/setns.2
index 18e80202326a..5985c099b464 100644
--- a/man2/setns.2
+++ b/man2/setns.2
@@ -131,8 +131,12 @@ capabilities in its own user namespace and
.BR CAP_SYS_ADMIN
in the user namespace that owns the target mount namespace.
.IP
-A process may not be reassociated with a new mount namespace if it is
-multithreaded.
+A process can't join a new mount namespace if it is sharing
+filesystem-related attributes
+(the attributes whose sharing is controlled by the
+.BR clone (2)
+.B CLONE_FS
+flag) with another process.
.\" Above check is in fs/namespace.c:mntns_install() [3.8 source]
.IP
See
--
2.23.0
