[Devel] [PATCH 1/1] Fix a panic while mouting containers on powerpc and some other small cleanups (Re: [ckrm-tech] [PATCH 4/6] containers: Simple CPU accounting container subsystem)

[Balbir Singh]

Balbir Singh wrote:
> Paul Menage wrote:
>> On 1/10/07, Balbir Singh <balbir at in.ibm.com> wrote:
>>> I have run into a problem running this patch on a powerpc box. Basically,
>>> the machine panics as soon as I mount the container filesystem with
>> This is a multi-processor system?
>>
> Hi, Paul,
> 
> I figured out the reason for the panic. Here are the fixes
> 

Here is the second patch and the real fix in sched.c

Fix coding style in cpuacct_charge()

In sched.c, account_user_time() can be called with the task p set to rq->idle.
Since idle tasks do not belong to any container, this was causing a panic in
task_ca() in cpu_acct.c.

Multiplying the time by 1000 is not correct in cpuusage_read(). The code
has been converted to use the correct cputime API.

Add mount/umount callbacks.

Signed-off-by: Balbir Singh <balbir at in.ibm.com>
---

 kernel/cpu_acct.c |   29 +++++++++++++++++++++++------
 kernel/sched.c    |   17 +++++++++++------
 2 files changed, 34 insertions(+), 12 deletions(-)

diff -puN kernel/cpu_acct.c~fix-cpuacct-panic-on-mount kernel/cpu_acct.c
--- linux-2.6.20-rc3/kernel/cpu_acct.c~fix-cpuacct-panic-on-mount	2007-01-15
14:23:20.000000000 +0530
+++ linux-2.6.20-rc3-balbir/kernel/cpu_acct.c	2007-01-15 14:23:20.000000000 +0530
@@ -22,6 +22,7 @@ struct cpuacct {
 };

 static struct container_subsys cpuacct_subsys;
+static struct container *root;

 static inline struct cpuacct *container_ca(struct container *cont)
 {
@@ -49,6 +50,16 @@ static void cpuacct_destroy(struct conta
 	kfree(container_ca(cont));
 }

+static void cpuacct_mount(struct container_subsys *ss, struct container *cont)
+{
+	root = cont;
+}
+
+static void cpuacct_umount(struct container_subsys *ss, struct container *cont)
+{
+	root = NULL;
+}
+
 static ssize_t cpuusage_read(struct container *cont,
 			     struct cftype *cft,
 			     struct file *file,
@@ -57,6 +68,7 @@ static ssize_t cpuusage_read(struct cont
 {
 	struct cpuacct *ca = container_ca(cont);
 	cputime64_t time;
+	unsigned long time_in_jiffies;
 	char usagebuf[64];
 	char *s = usagebuf;

@@ -64,9 +76,8 @@ static ssize_t cpuusage_read(struct cont
 	time = ca->time;
 	spin_unlock_irq(&ca->lock);

-	time *= 1000;
-	do_div(time, HZ);
-	s += sprintf(s, "%llu", (unsigned long long) time);
+	time_in_jiffies = cputime_to_jiffies(time);
+	s += sprintf(s, "%llu\n", (unsigned long long) time_in_jiffies);

 	return simple_read_from_buffer(buf, nbytes, ppos, usagebuf, s - usagebuf);
 }
@@ -83,12 +94,13 @@ static int cpuacct_populate(struct conta
 }


-void cpuacct_charge(struct task_struct *task, cputime_t cputime) {
+void cpuacct_charge(struct task_struct *task, cputime_t cputime)
+{

 	struct cpuacct *ca;
 	unsigned long flags;

-	if (cpuacct_subsys.subsys_id < 0) return;
+	if (cpuacct_subsys.subsys_id < 0 || !root) return;
 	rcu_read_lock();
 	ca = task_ca(task);
 	if (ca) {
@@ -104,13 +116,18 @@ static struct container_subsys cpuacct_s
 	.create = cpuacct_create,
 	.destroy = cpuacct_destroy,
 	.populate = cpuacct_populate,
+	.mount = cpuacct_mount,
+	.umount = cpuacct_umount,
 	.subsys_id = -1,
 };


 int __init init_cpuacct(void)
 {
-	int id = container_register_subsys(&cpuacct_subsys);
+	int id;
+
+	root = NULL;
+	id = container_register_subsys(&cpuacct_subsys);
 	return id < 0 ? id : 0;
 }

diff -puN kernel/sched.c~fix-cpuacct-panic-on-mount kernel/sched.c
--- linux-2.6.20-rc3/kernel/sched.c~fix-cpuacct-panic-on-mount	2007-01-15
14:23:20.000000000 +0530
+++ linux-2.6.20-rc3-balbir/kernel/sched.c	2007-01-15 14:23:20.000000000 +0530
@@ -3067,10 +3067,17 @@ void account_user_time(struct task_struc
 {
 	struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
 	cputime64_t tmp;
+	struct rq *rq = this_rq();

 	p->utime = cputime_add(p->utime, cputime);

-	cpuacct_charge(p, cputime);
+	/*
+	 * On powerpc this routine can be called with p set to the idle
+	 * task of the cpu. idle tasks don't really belong to any
+	 * container.
+	 */
+	if (p != rq->idle)
+		cpuacct_charge(p, cputime);

 	/* Add user time to cpustat. */
 	tmp = cputime_to_cputime64(cputime);
@@ -3095,18 +3102,16 @@ void account_system_time(struct task_str

 	p->stime = cputime_add(p->stime, cputime);

-	if (p != rq->idle)
-		cpuacct_charge(p, cputime);
-
 	/* Add system time to cpustat. */
 	tmp = cputime_to_cputime64(cputime);
 	if (hardirq_count() - hardirq_offset)
 		cpustat->irq = cputime64_add(cpustat->irq, tmp);
 	else if (softirq_count())
 		cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
-	else if (p != rq->idle)
+	else if (p != rq->idle) {
 		cpustat->system = cputime64_add(cpustat->system, tmp);
-	else if (atomic_read(&rq->nr_iowait) > 0)
+		cpuacct_charge(p, cputime);
+	} else if (atomic_read(&rq->nr_iowait) > 0)
 		cpustat->iowait = cputime64_add(cpustat->iowait, tmp);
 	else
 		cpustat->idle = cputime64_add(cpustat->idle, tmp);
_

	Balbir Singh
	Linux Technology Center
	Bangalore, IBM ISTL