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bpf: Fix bpf_iter's task iterator logic

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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.

Fixes: eaaacd2391 ("bpf: Add task and task/file iterator targets")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200514055137.1564581-1-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2020-05-13 22:51:37 -07:00 committed by Alexei Starovoitov
parent 0645f7eb6f
commit c70f34a8ac
1 changed files with 7 additions and 1 deletions
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8
kernel/bpf/task_iter.c
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@ -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;