[PATCH 2/2] proc: don't show PF_IO_WORKER threads as threads in /proc//task/

Jens Axboe
2021-03-25T16:44:39Z

We don't allow SIGSTOP and ptrace attach to these threads, and that
confuses applications like gdb that assume they can attach to any thread
listed in /proc/<pid>/task/. gdb then enters an infinite loop of retrying
attach, even though it fails with the same error (-EPERM) every time.

Skip over PF_IO_WORKER threads in the proc task setup. We can't just
terminate the when we find a PF_IO_WORKER thread, as there's no real
ordering here. It's perfectly feasible to have the first thread be an
IO worker, and then a real thread after that. Hence just implement the
skip.

Reported-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/proc/base.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3851bfcdba56..abff2fe10bfa 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3723,7 +3723,7 @@ static struct task_struct *first_tid(struct pid *pid, int tid, loff_t f_pos,
*/
pos = task = task->group_leader;
do {
- if (!nr--)
+ if (same_thread_group(task, pos) && !nr--)
goto found;
} while_each_thread(task, pos);
fail:
@@ -3744,16 +3744,22 @@ static struct task_struct *first_tid(struct pid *pid, int tid, loff_t f_pos,
*/
static struct task_struct *next_tid(struct task_struct *start)
{
- struct task_struct *pos = NULL;
+ struct task_struct *tmp, *pos = NULL;
+
rcu_read_lock();
- if (pid_alive(start)) {
- pos = next_thread(start);
- if (thread_group_leader(pos))
- pos = NULL;
- else
- get_task_struct(pos);
+ if (!pid_alive(start))
+ goto no_thread;
+ list_for_each_entry_rcu(tmp, &start->thread_group, thread_group) {
+ if (!thread_group_leader(tmp) && same_thread_group(start, tmp)) {
+ get_task_struct(tmp);
+ pos = tmp;
+ break;
+ }
}
+no_thread:
rcu_read_unlock();
+ if (!pos)
+ return NULL;
put_task_struct(start);
return pos;
}
--
2.31.0