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    Subject[PATCH 14/16] tracing: Dont use tracing_record_cmdline() in workqueue tracer fix
    From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

    commit c3ffc7a40b7e94b094efe1c8ab4e24370a782b65
    "Don't use tracing_record_cmdline() in workqueue tracer"
    has a race window.

    find_task_by_vpid() requires task_list_lock().

    LKML-Reference: <20090313090042.43CD.A69D9226@jp.fujitsu.com>
    Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: Steven Rostedt <srostedt@redhat.com>
    ---
    kernel/trace/trace_workqueue.c | 20 ++++++++++++++------
    1 files changed, 14 insertions(+), 6 deletions(-)

    diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
    index fb5ccac..9ab035b 100644
    --- a/kernel/trace/trace_workqueue.c
    +++ b/kernel/trace/trace_workqueue.c
    @@ -193,12 +193,20 @@ static int workqueue_stat_show(struct seq_file *s, void *p)
    struct cpu_workqueue_stats *cws = p;
    unsigned long flags;
    int cpu = cws->cpu;
    - struct task_struct *tsk = find_task_by_vpid(cws->pid);
    -
    - seq_printf(s, "%3d %6d %6u %s\n", cws->cpu,
    - atomic_read(&cws->inserted),
    - cws->executed,
    - tsk ? tsk->comm : "<...>");
    + struct pid *pid;
    + struct task_struct *tsk;
    +
    + pid = find_get_pid(cws->pid);
    + if (pid) {
    + tsk = get_pid_task(pid, PIDTYPE_PID);
    + if (tsk) {
    + seq_printf(s, "%3d %6d %6u %s\n", cws->cpu,
    + atomic_read(&cws->inserted), cws->executed,
    + tsk->comm);
    + put_task_struct(tsk);
    + }
    + put_pid(pid);
    + }

    spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
    if (&cws->list == workqueue_cpu_stat(cpu)->list.next)
    --
    1.6.1.3
    --


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