bpf: Avoid iterating duplicated files for task_file iterator (203d7b05) · Commits · 戴 / test

Currently, task_file iterator iterates all files from all tasks. This may potentially visit a lot of duplicated files if there are many tasks sharing the same files, e.g., typical pthreads where these pthreads and the main thread are sharing the same files. This patch changed task_file iterator to skip a particular task if that task shares the same files as its group_leader (the task having the same tgid and also task->tgid == task->pid). This will preserve the same result, visiting all files from all tasks, and will reduce runtime cost significantl, e.g., if there are a lot of pthreads and the process has a lot of open files. Suggested-by:

Andrii Nakryiko <andriin@fb.com> Signed-off-by:

Yonghong Song <yhs@fb.com> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net> Reviewed-by:

Josef Bacik <josef@toxicpanda.com> Link: https://lore.kernel.org/bpf/20200902023112.1672792-1-yhs@fb.com

kernel/bpf/task_iter.c

+11 −4

Original line number	Diff line number	Diff line
		@@ -22,7 +22,8 @@ struct bpf_iter_seq_task_info {
		};

		static struct task_struct task_seq_get_next(struct pid_namespace ns,
		u32 *tid)
		u32 *tid,
		bool skip_if_dup_files)
		{
		struct task_struct *task = NULL;
		struct pid *pid;
		@@ -36,6 +37,12 @@ retry:
		if (!task) {
		++*tid;
		goto retry;
		} else if (skip_if_dup_files && task->tgid != task->pid &&
		task->files == task->group_leader->files) {
		put_task_struct(task);
		task = NULL;
		++*tid;
		goto retry;
		}
		}
		rcu_read_unlock();
		@@ -48,7 +55,7 @@ static void task_seq_start(struct seq_file seq, loff_t *pos)
		struct bpf_iter_seq_task_info *info = seq->private;
		struct task_struct *task;

		task = task_seq_get_next(info->common.ns, &info->tid);
		task = task_seq_get_next(info->common.ns, &info->tid, false);
		if (!task)
		return NULL;

		@@ -65,7 +72,7 @@ static void task_seq_next(struct seq_file seq, void v, loff_t pos)
		++*pos;
		++info->tid;
		put_task_struct((struct task_struct *)v);
		task = task_seq_get_next(info->common.ns, &info->tid);
		task = task_seq_get_next(info->common.ns, &info->tid, false);
		if (!task)
		return NULL;

		@@ -148,7 +155,7 @@ again:
		curr_files = *fstruct;
		curr_fd = info->fd;
		} else {
		curr_task = task_seq_get_next(ns, &curr_tid);
		curr_task = task_seq_get_next(ns, &curr_tid, true);
		if (!curr_task)
		return NULL;

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