ipc: do not use a negative value to re-enable msgmni automatic recomputing
This patch proposes an alternative to the "magical
positive-versus-negative number trick" Andrew complained about last week
in http://lkml.org/lkml/2008/6/24/418.
This had been introduced with the patches that scale msgmni to the amount
of lowmem. With these patches, msgmni has a registered notification
routine that recomputes msgmni value upon memory add/remove or ipc
namespace creation/ removal.
When msgmni is changed from user space (i.e. value written to the proc
file), that notification routine is unregistered, and the way to make it
registered back is to write a negative value into the proc file. This is
the "magical positive-versus-negative number trick".
To fix this, a new proc file is introduced: /proc/sys/kernel/auto_msgmni.
This file acts as ON/OFF for msgmni automatic recomputing.
With this patch, the process is the following:
1) kernel boots in "automatic recomputing mode"
/proc/sys/kernel/msgmni contains the value that has been computed (depends
on lowmem)
/proc/sys/kernel/automatic_msgmni contains "1"
2) echo <val> > /proc/sys/kernel/msgmni
. sets msg_ctlmni to <val>
. de-activates automatic recomputing (i.e. if, say, some memory is added
msgmni won't be recomputed anymore)
. /proc/sys/kernel/automatic_msgmni now contains "0"
3) echo "0" > /proc/sys/kernel/automatic_msgmni
. de-activates msgmni automatic recomputing
this has the same effect as 2) except that msg_ctlmni's value stays
blocked at its current value)
3) echo "1" > /proc/sys/kernel/automatic_msgmni
. recomputes msgmni's value based on the current available memory size
and number of ipc namespaces
. re-activates automatic recomputing for msgmni.
Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Solofo Ramangalahy <Solofo.Ramangalahy@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index d349746..69bc859 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -27,15 +27,17 @@
}
/*
- * 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.
+ * Routine that is called when the file "auto_msgmni" has successfully been
+ * written.
+ * Two values are allowed:
+ * 0: unregister msgmni's callback routine from the ipc namespace notifier
+ * chain. This means that msgmni won't be recomputed anymore upon memory
+ * add/remove or ipc namespace creation/removal.
+ * 1: register back the callback routine.
*/
-static void tunable_set_callback(int val)
+static void ipc_auto_callback(int val)
{
- if (val >= 0)
+ if (!val)
unregister_ipcns_notifier(current->nsproxy->ipc_ns);
else {
/*
@@ -71,7 +73,12 @@
rc = proc_dointvec(&ipc_table, write, filp, buffer, lenp, ppos);
if (write && !rc && lenp_bef == *lenp)
- tunable_set_callback(*((int *)(ipc_table.data)));
+ /*
+ * Tunable has successfully been changed by hand. Disable its
+ * automatic adjustment. This simply requires unregistering
+ * the notifiers that trigger recalculation.
+ */
+ unregister_ipcns_notifier(current->nsproxy->ipc_ns);
return rc;
}
@@ -87,10 +94,39 @@
lenp, ppos);
}
+static int proc_ipcauto_dointvec_minmax(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 oldval;
+ int rc;
+
+ memcpy(&ipc_table, table, sizeof(ipc_table));
+ ipc_table.data = get_ipc(table);
+ oldval = *((int *)(ipc_table.data));
+
+ rc = proc_dointvec_minmax(&ipc_table, write, filp, buffer, lenp, ppos);
+
+ if (write && !rc && lenp_bef == *lenp) {
+ int newval = *((int *)(ipc_table.data));
+ /*
+ * The file "auto_msgmni" has correctly been set.
+ * React by (un)registering the corresponding tunable, if the
+ * value has changed.
+ */
+ if (newval != oldval)
+ ipc_auto_callback(newval);
+ }
+
+ return rc;
+}
+
#else
#define proc_ipc_doulongvec_minmax NULL
#define proc_ipc_dointvec NULL
#define proc_ipc_callback_dointvec NULL
+#define proc_ipcauto_dointvec_minmax NULL
#endif
#ifdef CONFIG_SYSCTL_SYSCALL
@@ -142,14 +178,11 @@
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
*/
- int *data = get_ipc(table);
-
- tunable_set_callback(*data);
- }
+ unregister_ipcns_notifier(current->nsproxy->ipc_ns);
return rc;
}
@@ -158,6 +191,9 @@
#define sysctl_ipc_registered_data NULL
#endif
+static int zero;
+static int one = 1;
+
static struct ctl_table ipc_kern_table[] = {
{
.ctl_name = KERN_SHMMAX,
@@ -222,6 +258,16 @@
.proc_handler = proc_ipc_dointvec,
.strategy = sysctl_ipc_data,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "auto_msgmni",
+ .data = &init_ipc_ns.auto_msgmni,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_ipcauto_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
{}
};