From 8feebc6713cd78cbba8c4e2a6d92299669052026 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 27 Apr 2020 14:32:54 -0500 Subject: [PATCH] posix-cpu-timer: Tidy up group_leader logic in lookup_task Replace has_group_leader_pid with thread_group_leader. Years ago Oleg suggested changing thread_group_leader to has_group_leader_pid to handle races. Looking at the code then and now I don't see how it ever helped. Especially as then the code really did need to be the thread_group_leader. Today it doesn't make a difference if thread_group_leader races with de_thread as the task returned from lookup_task in the non-thread case is just used to find values in task->signal. Since the races with de_thread have never been handled revert has_group_header_pid to thread_group_leader for clarity. Update the comment in lookup_task to remove implementation details that are no longer true and to mention task->signal instead of task->sighand, as the relevant cpu timer details are all in task->signal. Ref: 55e8c8eb2c7b ("posix-cpu-timers: Store a reference to a pid not a task") Ref: c0deae8c9587 ("posix-cpu-timers: Rcu_read_lock/unlock protect find_task_by_vpid call") Signed-off-by: "Eric W. Biederman" --- kernel/time/posix-cpu-timers.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 2fd3b3fa68bf..e4051e417bcb 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -69,12 +69,8 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread, if (gettime) { /* * For clock_gettime(PROCESS) the task does not need to be - * the actual group leader. tsk->sighand gives + * the actual group leader. task->signal gives * access to the group's clock. - * - * Timers need the group leader because they take a - * reference on it and store the task pointer until the - * timer is destroyed. */ return (p == current || thread_group_leader(p)) ? p : NULL; } @@ -82,7 +78,7 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread, /* * For processes require that p is group leader. */ - return has_group_leader_pid(p) ? p : NULL; + return thread_group_leader(p) ? p : NULL; } static struct task_struct *__get_task_for_clock(const clockid_t clock,