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Subject[patch 5/7] oom: fix possible oom_dump_tasks NULL pointer
When /proc/sys/vm/oom_dump_tasks is enabled, it is possible to get a NULL
pointer for tasks that have detached mm's since task_lock() is not held
during the tasklist scan.

Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/oom_kill.c | 24 +++++++++++++++---------
1 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -284,22 +284,28 @@ static void dump_tasks(const struct mem_cgroup *mem)
printk(KERN_INFO "[ pid ] uid tgid total_vm rss cpu oom_adj "
"name\n");
do_each_thread(g, p) {
- /*
- * total_vm and rss sizes do not exist for tasks with a
- * detached mm so there's no need to report them.
- */
- if (!p->mm)
- continue;
+ struct mm_struct *mm;
+
if (mem && !task_in_mem_cgroup(p, mem))
continue;
if (!thread_group_leader(p))
continue;

task_lock(p);
+ mm = p->mm;
+ if (!mm) {
+ /*
+ * total_vm and rss sizes do not exist for tasks with no
+ * mm so there's no need to report them; they can't be
+ * oom killed anyway.
+ */
+ task_unlock(p);
+ continue;
+ }
printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d %3d %s\n",
- p->pid, __task_cred(p)->uid, p->tgid,
- p->mm->total_vm, get_mm_rss(p->mm), (int)task_cpu(p),
- p->oomkilladj, p->comm);
+ p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
+ get_mm_rss(mm), (int)task_cpu(p), p->oomkilladj,
+ p->comm);
task_unlock(p);
} while_each_thread(g, p);
}

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