On 8/21/23 13:32, Kui-Feng Lee wrote:
On 8/21/23 13:03, Oleg Nesterov wrote:
get_pid_task() makes no sense, the code does put_task_struct() soon
after.
Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill
kill put_task_struct(), this allows to do get_task_struct() only once
before return.
While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)"
block, this matches the next usage of find_pid_ns() + get_pid_task() in
this function.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
kernel/bpf/task_iter.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 4d1125108014..1589ec3faded 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -42,9 +42,6 @@ static struct task_struct
*task_group_seq_get_next(struct bpf_iter_seq_task_comm
if (!*tid) {
/* The first time, the iterator calls this function. */
pid = find_pid_ns(common->pid, common->ns);
- if (!pid)
- return NULL;
-
task = get_pid_task(pid, PIDTYPE_TGID);
if (!task)
return NULL;
@@ -66,17 +63,12 @@ static struct task_struct
*task_group_seq_get_next(struct bpf_iter_seq_task_comm
return task;
}
- pid = find_pid_ns(common->pid_visiting, common->ns);
- if (!pid)
- return NULL;
-
- task = get_pid_task(pid, PIDTYPE_PID);
+ task = find_task_by_pid_ns(common->pid_visiting, common->ns);
if (!task)
return NULL;
retry:
next_task = next_thread(task);
- put_task_struct(task);
It called get_task_struct() against this task to hold a refcount at the
previous time calling this function. When will it release the refcount?
Oh! I missed the fact that the caller will handle it.
saved_tid = *tid;
*tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns);
@@ -88,7 +80,6 @@ static struct task_struct
*task_group_seq_get_next(struct bpf_iter_seq_task_comm
return NULL;
}
- get_task_struct(next_task);
common->pid_visiting = *tid;
if (skip_if_dup_files && task->files ==
task->group_leader->files) {
@@ -96,6 +87,7 @@ static struct task_struct
*task_group_seq_get_next(struct bpf_iter_seq_task_comm
goto retry;
}
+ get_task_struct(next_task);
return next_task;
}
