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Date: Thu, 3 Dec 2020 13:59:07 -0800 From: Jonathan Lemon <jonathan.lemon@...il.com> To: <netdev@...r.kernel.org>, <ast@...nel.org>, <daniel@...earbox.net>, <yhs@...com> CC: <kernel-team@...com> Subject: [PATCH bpf-next] bpf: increment and use correct thread iterator From: Jonathan Lemon <bsd@...com> If unable to obtain the file structure for the current task, proceed to the next task number after the one returned from task_seq_get_next(), instead of the next task number from the original iterator. Use thread_group_leader() instead of comparing tgid vs pid, which might may be racy. Only obtain the task reference count at the end of the RCU section instead of repeatedly obtaining/releasing it when iterathing though a thread group. This patch fixes a recurring RCU stall seen from task_file_seq_next(). Fixes: a650da2ee52a ("bpf: Add task and task/file iterator targets") Fixes: 67b6b863e6ab ("bpf: Avoid iterating duplicated files for task_file iterator") Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com> --- kernel/bpf/task_iter.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index 0458a40edf10..66a52fcf589a 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -33,17 +33,17 @@ static struct task_struct *task_seq_get_next(struct pid_namespace *ns, pid = find_ge_pid(*tid, ns); if (pid) { *tid = pid_nr_ns(pid, ns); - task = get_pid_task(pid, PIDTYPE_PID); + task = pid_task(pid, PIDTYPE_PID); if (!task) { ++*tid; goto retry; - } else if (skip_if_dup_files && task->tgid != task->pid && + } else if (skip_if_dup_files && !thread_group_leader(task) && task->files == task->group_leader->files) { - put_task_struct(task); task = NULL; ++*tid; goto retry; } + get_task_struct(task); } rcu_read_unlock(); @@ -164,7 +164,7 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info) curr_files = get_files_struct(curr_task); if (!curr_files) { put_task_struct(curr_task); - curr_tid = ++(info->tid); + curr_tid = curr_tid + 1; info->fd = 0; goto again; } -- 2.24.1
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