diff options
| author | Oleg Nesterov <oleg@redhat.com> | 2023-08-23 20:08:06 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-08-25 02:25:15 +0300 |
| commit | dce8f8ed1de1d9d6d27c5ccd202ce4ec163b100c (patch) | |
| tree | 93e6156402383138221d53cb0937d28cefa97cf0 | |
| parent | ed1af26cd24811c3ddb5e7a276e3c6362c989bba (diff) | |
| download | linux-dce8f8ed1de1d9d6d27c5ccd202ce4ec163b100c.tar.xz | |
document while_each_thread(), change first_tid() to use for_each_thread()
Add the comment to explain that while_each_thread(g,t) is not rcu-safe
unless g is stable (e.g. current). Even if g is a group leader and thus
can't exit before t, t or another sub-thread can exec and remove g from
the thread_group list.
The only lockless user of while_each_thread() is first_tid() and it is
fine in that it can't loop forever, yet for_each_thread() looks better and
I am going to change while_each_thread/next_thread.
Link: https://lkml.kernel.org/r/20230823170806.GA11724@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | fs/proc/base.c | 5 | ||||
| -rw-r--r-- | include/linux/sched/signal.h | 4 |
2 files changed, 6 insertions, 3 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c index 05452c3b9872..483a3edebdd1 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -3813,11 +3813,10 @@ static struct task_struct *first_tid(struct pid *pid, int tid, loff_t f_pos, /* If we haven't found our starting place yet start * with the leader and walk nr threads forward. */ - pos = task = task->group_leader; - do { + for_each_thread(task, pos) { if (!nr--) goto found; - } while_each_thread(task, pos); + }; fail: pos = NULL; goto out; diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 0deebe2ab07d..0014d3adaf84 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -648,6 +648,10 @@ extern void flush_itimer_signals(void); extern bool current_is_single_threaded(void); +/* + * Without tasklist/siglock it is only rcu-safe if g can't exit/exec, + * otherwise next_thread(t) will never reach g after list_del_rcu(g). + */ #define while_each_thread(g, t) \ while ((t = next_thread(t)) != g) |