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Subject[PATCH] oprofile: hotplug cpu fix
This patch addresses crashes when hotplugging cpus while profiling.
I used the following script to test :

#!/bin/bash
startup()
{
opcontrol --init
opcontrol --vmlinux=/boot/vmlinux
opcontrol --reset
opcontrol --start
opcontrol --dump
}
shutdown()
{
opcontrol --dump
opcontrol -h
}
startup
echo 0 > /sys/devices/system/cpu/cpu2/online
echo 0 > /sys/devices/system/cpu/cpu1/online
shutdown
startup
echo 1 > /sys/devices/system/cpu/cpu2/online
echo 1 > /sys/devices/system/cpu/cpu1/online
shutdown
startup
echo 0 > /sys/devices/system/cpu/cpu2/online
shutdown
startup
echo 1 > /sys/devices/system/cpu/cpu2/online
echo 0 > /sys/devices/system/cpu/cpu2/online
shutdown
echo 1 > /sys/devices/system/cpu/cpu2/online

Without the patch on my Power machine (ppc970mp) I get the following error:

Vector: 300 (Data Access) at [c000000276143950]
pc: d0000000000366e8: .add_event_entry+0x60/0xb0 [oprofile]
lr: d000000000035e60: .sync_buffer+0x68/0x4ac [oprofile]

Without the patch on my x86 (Core 2 Duo) machine:

mutex_lock +0x8/0x20
sync_buffer +0x29/0x3e0
wq_sync_buffer +0x0/0x70

Since I'm guessing hotplugging cpus and using oprofile is not a common
occurrence, this patch is just a do-no-harm fix, instead
of a full solution with a hotplug callback, etc.

Thanks,
--chris

From 60f07301d3c387a0405becccbdc0cfb7e99ecf39 Mon Sep 17 00:00:00 2001
From: Chris J Arges <arges@linux.vnet.ibm.com>
Date: Wed, 15 Oct 2008 11:03:39 -0500
Subject: [PATCH] oprofile: hotplug cpu fix
This patch addresses problems when hotplugging cpus while profiling.
Instead of allocating only online cpus, all possible cpu buffers are
allocated, which allows cpus to be onlined during operation. If a cpu is
offlined before profiling is shutdown wq_sync_buffer checks for this
condition then cancels this work and does not sync this buffer.

---
drivers/oprofile/cpu_buffer.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/oprofile/cpu_buffer.c b/drivers/oprofile/cpu_buffer.c
index e1bd5a9..8bb030b 100644
--- a/drivers/oprofile/cpu_buffer.c
+++ b/drivers/oprofile/cpu_buffer.c
@@ -39,7 +39,7 @@ void free_cpu_buffers(void)
{
int i;

- for_each_online_cpu(i) {
+ for_each_possible_cpu(i) {
vfree(per_cpu(cpu_buffer, i).buffer);
per_cpu(cpu_buffer, i).buffer = NULL;
}
@@ -51,7 +51,7 @@ int alloc_cpu_buffers(void)

unsigned long buffer_size = fs_cpu_buffer_size;

- for_each_online_cpu(i) {
+ for_each_possible_cpu(i) {
struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);

b->buffer = vmalloc_node(sizeof(struct op_sample) * buffer_size,
@@ -368,6 +368,11 @@ static void wq_sync_buffer(struct work_struct *work)
if (b->cpu != smp_processor_id()) {
printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
smp_processor_id(), b->cpu);
+
+ if (!cpu_online(b->cpu)) {
+ cancel_delayed_work(&b->work);
+ return;
+ }
}
sync_buffer(b->cpu);

--
1.5.4.5
Signed-off-by: Chris J Arges <arges@linux.vnet.ibm.com>



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