ipc/msg: increase MSGMNI, remove scaling

SysV can be abused to allocate locked kernel memory.  For most systems, a
small limit doesn't make sense, see the discussion with regards to SHMMAX.

Therefore: increase MSGMNI to the maximum supported.

And: If we ignore the risk of locking too much memory, then an automatic
scaling of MSGMNI doesn't make sense.  Therefore the logic can be removed.

The code preserves auto_msgmni to avoid breaking any user space applications
that expect that the value exists.

Notes:
1) If an administrator must limit the memory allocations, then he can set
MSGMNI as necessary.

Or he can disable sysv entirely (as e.g. done by Android).

2) MSGMAX and MSGMNB are intentionally not increased, as these values are used
to control latency vs. throughput:
If MSGMNB is large, then msgsnd() just returns and more messages can be queued
before a task switch to a task that calls msgrcv() is forced.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 22 deletions

diff --git a/ipc/namespace.c b/ipc/namespace.c
index b54468e48e32..1a3ffd40356e 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -45,14 +45,6 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
         msg_init_ns(ns);
         shm_init_ns(ns);
 
-        /*
-         * msgmni has already been computed for the new ipc ns.
-         * Thus, do the ipcns creation notification before registering that
-         * new ipcns in the chain.
-         */
-        ipcns_notify(IPCNS_CREATED);
-        register_ipcns_notifier(ns);
-
         ns->user_ns = get_user_ns(user_ns);
 
         return ns;
@@ -99,25 +91,11 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
 
 static void free_ipc_ns(struct ipc_namespace *ns)
 {
-        /*
-         * Unregistering the hotplug notifier at the beginning guarantees
-         * that the ipc namespace won't be freed while we are inside the
-         * callback routine. Since the blocking_notifier_chain_XXX routines
-         * hold a rw lock on the notifier list, unregister_ipcns_notifier()
-         * won't take the rw lock before blocking_notifier_call_chain() has
-         * released the rd lock.
-         */
-        unregister_ipcns_notifier(ns);
         sem_exit_ns(ns);
         msg_exit_ns(ns);
         shm_exit_ns(ns);
         atomic_dec(&nr_ipc_ns);
 
-        /*
-         * Do the ipcns removal notification after decrementing nr_ipc_ns in
-         * order to have a correct value when recomputing msgmni.
-         */
-        ipcns_notify(IPCNS_REMOVED);
         put_user_ns(ns->user_ns);
         proc_free_inum(ns->proc_inum);
         kfree(ns);