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Commit 9eefe520 authored by Nadia Derbey's avatar Nadia Derbey Committed by Linus Torvalds
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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: default avatarNadia Derbey <Nadia.Derbey@bull.net>
Cc: Solofo Ramangalahy <Solofo.Ramangalahy@bull.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f1a43f93

include/linux/ipc_namespace.h

+2 −1
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ struct ipc_namespace { 
	int		msg_ctlmni;

	atomic_t	msg_bytes;

	atomic_t	msg_hdrs;

	int		auto_msgmni;



	size_t		shm_ctlmax;

	size_t		shm_ctlall;
@@ -53,7 +54,7 @@ extern atomic_t nr_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 void unregister_ipcns_notifier(struct ipc_namespace *);

extern int ipcns_notify(unsigned long);



#else /* CONFIG_SYSVIPC */

ipc/ipc_sysctl.c

+59 −13
Original line number Diff line number Diff line
@@ -27,15 +27,17 @@ static void *get_ipc(ctl_table *table) 
}



/*

 * 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

 * 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.

 * They can come back to a recomputable state by being set to a <0 value.

 * 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 @@ static int proc_ipc_callback_dointvec(ctl_table *table, int write, 
	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 @@ static int proc_ipc_doulongvec_minmax(ctl_table *table, int write, 
					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 @@ 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

		 */

		int *data = get_ipc(table);



		tunable_set_callback(*data);

	}

		unregister_ipcns_notifier(current->nsproxy->ipc_ns);



	return rc;

}
@@ -158,6 +191,9 @@ static int sysctl_ipc_registered_data(ctl_table *table, int __user *name, 
#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 @@ static struct ctl_table ipc_kern_table[] = { 
		.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,

	},

	{}

};

ipc/ipcns_notifier.c

+15 −5
Original line number Diff line number Diff line
@@ -55,25 +55,35 @@ static int ipcns_callback(struct notifier_block *self, 


int register_ipcns_notifier(struct ipc_namespace *ns)

{

	int rc;



	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_register(&ipcns_chain, &ns->ipcns_nb);

	rc = blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);

	if (!rc)

		ns->auto_msgmni = 1;

	return rc;

}



int cond_register_ipcns_notifier(struct ipc_namespace *ns)

{

	int rc;



	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,

	rc = blocking_notifier_chain_cond_register(&ipcns_chain,

							&ns->ipcns_nb);

	if (!rc)

		ns->auto_msgmni = 1;

	return rc;

}



int unregister_ipcns_notifier(struct ipc_namespace *ns)

void unregister_ipcns_notifier(struct ipc_namespace *ns)

{

	return blocking_notifier_chain_unregister(&ipcns_chain,

						&ns->ipcns_nb);

	blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);

	ns->auto_msgmni = 0;

}



int ipcns_notify(unsigned long val)