| Message ID | 20200514055137.1564581-1-andriin@fb.com |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [v2,bpf-next] bpf: fix bpf_iter's task iterator logic | expand |
On Wed, May 13, 2020 at 10:54 PM Andrii Nakryiko <andriin@fb.com> wrote: > > task_seq_get_next might stop prematurely if get_pid_task() fails to get > task_struct. Failure to do so doesn't mean that there are no more tasks with > higher pids. Procfs's iteration algorithm (see next_tgid in fs/proc/base.c) > does a retry in such case. After this fix, instead of stopping prematurely > after about 300 tasks on my server, bpf_iter program now returns >4000, which > sounds much closer to reality. > > Cc: Yonghong Song <yhs@fb.com> > Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets") > Acked-by: Yonghong Song <yhs@fb.com> > Signed-off-by: Andrii Nakryiko <andriin@fb.com> Applied. Thanks
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index a9b7264dda08..4dbf2b6035f8 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -27,9 +27,15 @@ static struct task_struct *task_seq_get_next(struct pid_namespace *ns, struct pid *pid; rcu_read_lock(); +retry: pid = idr_get_next(&ns->idr, tid); - if (pid) + if (pid) { task = get_pid_task(pid, PIDTYPE_PID); + if (!task) { + ++*tid; + goto retry; + } + } rcu_read_unlock(); return task;
task_seq_get_next might stop prematurely if get_pid_task() fails to get task_struct. Failure to do so doesn't mean that there are no more tasks with higher pids. Procfs's iteration algorithm (see next_tgid in fs/proc/base.c) does a retry in such case. After this fix, instead of stopping prematurely after about 300 tasks on my server, bpf_iter program now returns >4000, which sounds much closer to reality. Cc: Yonghong Song <yhs@fb.com> Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets") Acked-by: Yonghong Song <yhs@fb.com> Signed-off-by: Andrii Nakryiko <andriin@fb.com> --- kernel/bpf/task_iter.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)