linux-kernel - [PATCH 1/2] kernel: don't include PF_IO_WORKERs as part of same_thread

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Date:   Thu, 25 Mar 2021 10:43:42 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     io-uring@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, ebiederm@...ssion.com,
        linux-kernel@...r.kernel.org, oleg@...hat.com, metze@...ba.org,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 1/2] kernel: don't include PF_IO_WORKERs as part of same_thread_group()

Don't pretend that the IO threads are in the same thread group, the only
case where that seems to be desired is for accounting purposes. Add
a special accounting function for that and make the scheduler side use it.

For signals and ptrace, we don't allow them to be treated as threads
anyway.

Reported-by: Stefan Metzmacher <metze@...ba.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
---
 include/linux/sched/signal.h | 9 ++++++++-
 kernel/sched/cputime.c       | 2 +-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 3f6a0fcaa10c..4f621e386abf 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -668,11 +668,18 @@ static inline bool thread_group_leader(struct task_struct *p)
 }
 
 static inline
-bool same_thread_group(struct task_struct *p1, struct task_struct *p2)
+bool same_thread_group_account(struct task_struct *p1, struct task_struct *p2)
 {
 	return p1->signal == p2->signal;
 }
 
+static inline
+bool same_thread_group(struct task_struct *p1, struct task_struct *p2)
+{
+	return same_thread_group_account(p1, p2) &&
+			!((p1->flags | p2->flags) & PF_IO_WORKER);
+}
+
 static inline struct task_struct *next_thread(const struct task_struct *p)
 {
 	return list_entry_rcu(p->thread_group.next,
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 5f611658eeab..625110cacc2a 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -307,7 +307,7 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
 	 * those pending times and rely only on values updated on tick or
 	 * other scheduler action.
 	 */
-	if (same_thread_group(current, tsk))
+	if (same_thread_group_account(current, tsk))
 		(void) task_sched_runtime(current);
 
 	rcu_read_lock();
-- 
2.31.0