ipc: re-enable msgmni automatic recomputing msgmni if set to negative

The enhancement as asked for by Yasunori: if msgmni is set to a negative
value, register it back into the ipcns notifier chain.

A new interface has been added to the notification mechanism:
notifier_chain_cond_register() registers a notifier block only if not already
registered.  With that new interface we avoid taking care of the states
changes in procfs.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: Pierre Peiffer <pierre.peiffer@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index c3b1da9..ea6c18a 100644 (file)
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -52,6 +52,7 @@ extern atomic_t nr_ipc_ns;
 #define INIT_IPC_NS(ns)                .ns             = &init_ipc_ns,
 
 extern int register_ipcns_notifier(struct ipc_namespace *);
+extern int cond_register_ipcns_notifier(struct ipc_namespace *);
 extern int unregister_ipcns_notifier(struct ipc_namespace *);
 extern int ipcns_notify(unsigned long);
 

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 20dfed5..0ff6224 100644 (file)
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -121,6 +121,10 @@ extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
                struct notifier_block *nb);
 
+extern int blocking_notifier_chain_cond_register(
+               struct blocking_notifier_head *nh,
+               struct notifier_block *nb);
+
 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
                struct notifier_block *nb);
 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,

diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index d12ff5c..d349746 100644 (file)
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -15,6 +15,8 @@
 #include <linux/sysctl.h>
 #include <linux/uaccess.h>
 #include <linux/ipc_namespace.h>
+#include <linux/msg.h>
+#include "util.h"
 
 static void *get_ipc(ctl_table *table)
 {
@@ -24,6 +26,27 @@ static void *get_ipc(ctl_table *table)
        return which;
 }
 
+/*
+ * Routine that is called when a tunable has successfully been changed by
+ * hand and it has a callback routine registered on the ipc namespace notifier
+ * chain: we don't want such tunables to be recomputed anymore upon memory
+ * add/remove or ipc namespace creation/removal.
+ * They can come back to a recomputable state by being set to a <0 value.
+ */
+static void tunable_set_callback(int val)
+{
+       if (val >= 0)
+               unregister_ipcns_notifier(current->nsproxy->ipc_ns);
+       else {
+               /*
+                * Re-enable automatic recomputing only if not already
+                * enabled.
+                */
+               recompute_msgmni(current->nsproxy->ipc_ns);
+               cond_register_ipcns_notifier(current->nsproxy->ipc_ns);
+       }
+}
+
 #ifdef CONFIG_PROC_FS
 static int proc_ipc_dointvec(ctl_table *table, int write, struct file *filp,
        void __user *buffer, size_t *lenp, loff_t *ppos)
@@ -38,17 +61,17 @@ static int proc_ipc_dointvec(ctl_table *table, int write, struct file *filp,
 static int proc_ipc_callback_dointvec(ctl_table *table, int write,
        struct file *filp, void __user *buffer, size_t *lenp, loff_t *ppos)
 {
+       struct ctl_table ipc_table;
        size_t lenp_bef = *lenp;
        int rc;
 
-       rc = proc_ipc_dointvec(table, write, filp, buffer, lenp, ppos);
+       memcpy(&ipc_table, table, sizeof(ipc_table));
+       ipc_table.data = get_ipc(table);
+
+       rc = proc_dointvec(&ipc_table, write, filp, buffer, lenp, ppos);
 
        if (write && !rc && lenp_bef == *lenp)
-               /*
-                * Tunable has successfully been changed from userland:
-                * disable its automatic recomputing.
-                */
-               unregister_ipcns_notifier(current->nsproxy->ipc_ns);
+               tunable_set_callback(*((int *)(ipc_table.data)));
 
        return rc;
 }
@@ -119,12 +142,14 @@ static int sysctl_ipc_registered_data(ctl_table *table, int __user *name,
        rc = sysctl_ipc_data(table, name, nlen, oldval, oldlenp, newval,
                newlen);
 
-       if (newval && newlen && rc > 0)
+       if (newval && newlen && rc > 0) {
                /*
-                * Tunable has successfully been changed from userland:
-                * disable its automatic recomputing.
+                * Tunable has successfully been changed from userland
                 */
-               unregister_ipcns_notifier(current->nsproxy->ipc_ns);
+               int *data = get_ipc(table);
+
+               tunable_set_callback(*data);
+       }
 
        return rc;
 }

diff --git a/ipc/ipcns_notifier.c b/ipc/ipcns_notifier.c
index c797460..70ff091 100644 (file)
--- a/ipc/ipcns_notifier.c
+++ b/ipc/ipcns_notifier.c
@@ -61,6 +61,15 @@ int register_ipcns_notifier(struct ipc_namespace *ns)
        return blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
 }
 
+int cond_register_ipcns_notifier(struct ipc_namespace *ns)
+{
+       memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
+       ns->ipcns_nb.notifier_call = ipcns_callback;
+       ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
+       return blocking_notifier_chain_cond_register(&ipcns_chain,
+                                                       &ns->ipcns_nb);
+}
+
 int unregister_ipcns_notifier(struct ipc_namespace *ns)
 {
        return blocking_notifier_chain_unregister(&ipcns_chain,

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 643360d..823be11 100644 (file)
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -31,6 +31,21 @@ static int notifier_chain_register(struct notifier_block **nl,
        return 0;
 }
 
+static int notifier_chain_cond_register(struct notifier_block **nl,
+               struct notifier_block *n)
+{
+       while ((*nl) != NULL) {
+               if ((*nl) == n)
+                       return 0;
+               if (n->priority > (*nl)->priority)
+                       break;
+               nl = &((*nl)->next);
+       }
+       n->next = *nl;
+       rcu_assign_pointer(*nl, n);
+       return 0;
+}
+
 static int notifier_chain_unregister(struct notifier_block **nl,
                struct notifier_block *n)
 {
@@ -204,6 +219,29 @@ int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(blocking_notifier_chain_register);
 
+/**
+ *     blocking_notifier_chain_cond_register - Cond add notifier to a blocking notifier chain
+ *     @nh: Pointer to head of the blocking notifier chain
+ *     @n: New entry in notifier chain
+ *
+ *     Adds a notifier to a blocking notifier chain, only if not already
+ *     present in the chain.
+ *     Must be called in process context.
+ *
+ *     Currently always returns zero.
+ */
+int blocking_notifier_chain_cond_register(struct blocking_notifier_head *nh,
+               struct notifier_block *n)
+{
+       int ret;
+
+       down_write(&nh->rwsem);
+       ret = notifier_chain_cond_register(&nh->head, n);
+       up_write(&nh->rwsem);
+       return ret;
+}
+EXPORT_SYMBOL_GPL(blocking_notifier_chain_cond_register);
+
 /**
  *     blocking_notifier_chain_unregister - Remove notifier from a blocking notifier chain
  *     @nh: Pointer to head of the blocking notifier chain