The patch titled
Subject: change next_thread() to use __next_thread() ?: group_leader
has been added to the -mm mm-nonmm-unstable branch. Its filename is
change-next_thread-to-use-__next_thread-group_leader.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/change-next_thread-to-use-__next_thread-group_leader.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: change next_thread() to use __next_thread() ?: group_leader
Date: Thu, 24 Aug 2023 16:32:01 +0200
This relies on fact that group leader is always the 1st entry in the
signal->thread_head list.
With or without this change, if the lockless next_thread(last_thread)
races with exec it can return the old or the new leader.
We are almost ready to kill task->thread_group, after this change its
only user is thread_group_empty().
Link: https://lkml.kernel.org/r/20230824143201.GB31222@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched/signal.h | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- a/include/linux/sched/signal.h~change-next_thread-to-use-__next_thread-group_leader
+++ a/include/linux/sched/signal.h
@@ -726,10 +726,9 @@ static inline struct task_struct *__next
thread_node);
}
-static inline struct task_struct *next_thread(const struct task_struct *p)
+static inline struct task_struct *next_thread(struct task_struct *p)
{
- return list_entry_rcu(p->thread_group.next,
- struct task_struct, thread_group);
+ return __next_thread(p) ?: p->group_leader;
}
static inline int thread_group_empty(struct task_struct *p)
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
introduce-__next_thread-fix-next_tid-vs-exec-race.patch
change-next_thread-to-use-__next_thread-group_leader.patch
change-thread_group_empty-to-use-task_struct-thread_node.patch
kill-task_struct-thread_group.patch
__kill_pgrp_info-simplify-the-calculation-of-return-value.patch
