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From: Oleg Nesterov on 1 Apr 2010 12:40
proc_oom_score(task) have a reference to task_struct, but that is all.
If this task was already released before we take tasklist_lock

- we can't use task->group_leader, it points to nowhere

- it is not safe to call badness() even if this task is
->group_leader, has_intersects_mems_allowed() assumes
it is safe to iterate over ->thread_group list.

- even worse, badness() can hit ->signal == NULL

Add the pid_alive() check to ensure __unhash_process() was not called.

Also, use "task" instead of task->group_leader. badness() should return
the same result for any sub-thread. Currently this is not true, but
this should be changed anyway.

Signed-off-by: Oleg Nesterov <oleg(a)redhat.com>
---

fs/proc/base.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- TTT/fs/proc/base.c~PROC_OOM_SCORE 2010-03-11 13:11:50.000000000 +0100
+++ TTT/fs/proc/base.c 2010-04-01 14:41:17.000000000 +0200
@@ -442,12 +442,13 @@ static const struct file_operations proc
unsigned long badness(struct task_struct *p, unsigned long uptime);
static int proc_oom_score(struct task_struct *task, char *buffer)
{
- unsigned long points;
+ unsigned long points = 0;
struct timespec uptime;

do_posix_clock_monotonic_gettime(&uptime);
read_lock(&tasklist_lock);
- points = badness(task->group_leader, uptime.tv_sec);
+ if (pid_alive(task))
+ points = badness(task, uptime.tv_sec);
read_unlock(&tasklist_lock);
return sprintf(buffer, "%lu\n", points);
}

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