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mq_init_ns() creates the mqueue mount with fc_mount_longterm(), so its ->mnt_ns is MNT_NS_INTERNAL. When setting up the mqueue or ipc sysctls or msg_init_ns() fails afterwards, create_ipc_ns() drops it with a plain mntput(). With ->mnt_ns set that takes the fast path of mntput_no_expire(). The count drops to zero and nothing ever kills the mount, so the mount and the mqueue superblock are leaked. Commitdc55e35f9e("ipc: Store mqueue sysctls in the ipc namespace") added the first failure path after mq_init_ns() and never dropped the mount. Commit7229d74e5e("ipc: create_ipc_ns: drop mqueue mount on sysctl setup failure") tried to fix that with a mntput() but that doesn't help for a long-term mount. Use kern_unmount(). free_ipc() open-codes the same thing for a namespace that made it. Fixes:dc55e35f9e("ipc: Store mqueue sysctls in the ipc namespace") Fixes:7229d74e5e("ipc: create_ipc_ns: drop mqueue mount on sysctl setup failure") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20261009-work-fixes-rcu-v1-5-7446d2d335e6@kernel.org Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>