[PATCH 2/4] tracing/workqueue: Avoid accessing task_struct's membervariable in stat file read

From: Zhaolei
Date: Tue Apr 28 2009 - 06:54:31 EST


Workqueue task maybe destroyed when read stat file.
We should avoid getting information from task_struct this time.

Signed-off-by: Zhao Lei <zhaolei@xxxxxxxxxxxxxx>
Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
kernel/trace/trace_workqueue.c | 50 ++++++++++++++++++++--------------------
1 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
index 7a07d17..51ed57e 100644
--- a/kernel/trace/trace_workqueue.c
+++ b/kernel/trace/trace_workqueue.c
@@ -28,14 +28,22 @@ struct workfunc_stats {

/* A cpu workqueue thread */
struct cpu_workqueue_stats {
- struct list_head list;
- int cpu;
- pid_t pid;
+ struct list_head list;
+ int cpu;
+
/* Protected by cpu workqueue lock */
- unsigned int inserted;
- unsigned int executed;
+ unsigned int inserted;
+ unsigned int executed;
/* list of struct workfunc_stats in this workqueue */
- struct list_head workfunclist;
+ struct list_head workfunclist;
+
+ /*
+ * the task maybe destroyed when we read stat file
+ * we define it to void * because we only use it as a identifier
+ */
+ void *task;
+ int pid;
+ char comm[TASK_COMM_LEN];
};

/* List of workqueue threads on one cpu */
@@ -93,7 +101,7 @@ probe_worklet_enqueue(struct task_struct *wq_thread, struct work_struct *work,

spin_lock_irqsave(&workqueue_cpu_stat(wqcpu)->lock, flags);
list_for_each_entry(node, &workqueue_cpu_stat(wqcpu)->list, list) {
- if (node->pid == wq_thread->pid) {
+ if (node->task == wq_thread) {
/* we ignore error of do_worklet_insertion */
do_worklet_enqueue(node, work);
goto found;
@@ -124,7 +132,7 @@ probe_worklet_execute(struct task_struct *wq_thread, struct work_struct *work)
spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);

list_for_each_entry(node, &workqueue_cpu_stat(cpu)->list, list)
- if (node->pid == wq_thread->pid) {
+ if (node->task == wq_thread) {
node->executed++;
goto found_wq;
}
@@ -163,7 +171,9 @@ static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
INIT_LIST_HEAD(&cws->list);
cws->cpu = cpu;

+ cws->task = wq_thread;
cws->pid = wq_thread->pid;
+ strncpy(cws->comm, wq_thread->comm, TASK_COMM_LEN);
INIT_LIST_HEAD(&cws->workfunclist);

/*
@@ -204,7 +214,7 @@ static void probe_workqueue_destruction(struct task_struct *wq_thread)
list) {
struct workfunc_stats *wfstat, *wfstatnext;

- if (node->pid != wq_thread->pid)
+ if (node->task != wq_thread)
continue;

list_for_each_entry_safe(wfstat, wfstatnext,
@@ -304,25 +314,15 @@ static int workqueue_stat_show(struct seq_file *s, void *p)
{
struct workfunc_stats *wfstat = p;
struct cpu_workqueue_stats *cws = wfstat->parent;
- struct pid *pid;
- struct task_struct *tsk;

if (!wfstat->func) {
/* It is first dummy node, need to print workqueue info */
- pid = find_get_pid(cws->pid);
- if (pid) {
- tsk = get_pid_task(pid, PIDTYPE_PID);
- if (tsk) {
- seq_printf(s, "%3d %6d %6u %s:%d\n",
- cws->cpu,
- cws->inserted,
- cws->executed,
- tsk->comm,
- cws->pid);
- put_task_struct(tsk);
- }
- put_pid(pid);
- }
+ seq_printf(s, "%3d %6d %6u %s:%d\n",
+ cws->cpu,
+ cws->inserted,
+ cws->executed,
+ cws->comm,
+ cws->pid);
} else {
/* It is effect node, need to print workfunc info */
int lastwf = list_is_last(&wfstat->list, &cws->workfunclist);
--
1.5.5.3


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