[PATCH 7/9] signal: Make individual tasks exiting a first class concept.

Eric W. Biederman
2021-06-24T19:03:02Z

Implement start_task_exit_locked and rewrite the de_thread logic
in exec using it.

Calling start_task_exit_locked is equivalent to asyncrhonously
calling exit(2) aka pthread_exit on a task.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/exec.c | 10 +++++++++-
include/linux/sched/jobctl.h | 2 ++
include/linux/sched/signal.h | 1 +
kernel/signal.c | 37 ++++++++++++++++--------------------
4 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 18594f11c31f..b6f50213f0a0 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1040,6 +1040,7 @@ static int de_thread(struct task_struct *tsk)
struct signal_struct *sig = tsk->signal;
struct sighand_struct *oldsighand = tsk->sighand;
spinlock_t *lock = &oldsighand->siglock;
+ struct task_struct *t;

if (thread_group_empty(tsk))
goto no_thread_group;
@@ -1058,7 +1059,14 @@ static int de_thread(struct task_struct *tsk)
}

sig->group_exit_task = tsk;
- sig->notify_count = zap_other_threads(tsk);
+ sig->group_stop_count = 0;
+ sig->notify_count = 0;
+ __for_each_thread(sig, t) {
+ if (t == tsk)
+ continue;
+ sig->notify_count++;
+ start_task_exit_locked(t, SIGKILL);
+ }
if (!thread_group_leader(tsk))
sig->notify_count--;

diff --git a/include/linux/sched/jobctl.h b/include/linux/sched/jobctl.h
index fa067de9f1a9..e94833b0c819 100644
--- a/include/linux/sched/jobctl.h
+++ b/include/linux/sched/jobctl.h
@@ -19,6 +19,7 @@ struct task_struct;
#define JOBCTL_TRAPPING_BIT 21 /* switching to TRACED */
#define JOBCTL_LISTENING_BIT 22 /* ptracer is listening for events */
#define JOBCTL_TRAP_FREEZE_BIT 23 /* trap for cgroup freezer */
+#define JOBCTL_TASK_EXITING_BIT 31 /* the task is exiting */

#define JOBCTL_STOP_DEQUEUED (1UL << JOBCTL_STOP_DEQUEUED_BIT)
#define JOBCTL_STOP_PENDING (1UL << JOBCTL_STOP_PENDING_BIT)
@@ -28,6 +29,7 @@ struct task_struct;
#define JOBCTL_TRAPPING (1UL << JOBCTL_TRAPPING_BIT)
#define JOBCTL_LISTENING (1UL << JOBCTL_LISTENING_BIT)
#define JOBCTL_TRAP_FREEZE (1UL << JOBCTL_TRAP_FREEZE_BIT)
+#define JOBCTL_TASK_EXITING (1UL << JOBCTL_TASK_EXITING_BIT)

#define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)
#define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index c007e55cb119..a958381ba4a9 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -429,6 +429,7 @@ static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
}

void start_group_exit(int exit_code);
+void start_task_exit_locked(struct task_struct *task, int exit_code);

void task_join_group_stop(struct task_struct *task);

diff --git a/kernel/signal.c b/kernel/signal.c
index 95a076af600a..afbc001220dd 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -264,6 +264,12 @@ static inline void print_dropped_signal(int sig)
current->comm, current->pid, sig);
}

+static void task_set_jobctl_exiting(struct task_struct *task, int exit_code)
+{
+ WARN_ON_ONCE(task->jobctl & ~JOBCTL_STOP_SIGMASK);
+ task->jobctl = JOBCTL_TASK_EXITING | (exit_code & JOBCTL_STOP_SIGMASK);
+}
+
/**
* task_set_jobctl_pending - set jobctl pending bits
* @task: target task
@@ -1407,28 +1413,15 @@ int force_sig_info(struct kernel_siginfo *info)
return force_sig_info_to_task(info, current, false);
}

-/*
- * Nuke all other threads in the group.
- */
-int zap_other_threads(struct task_struct *p)
+void start_task_exit_locked(struct task_struct *task, int exit_code)
{
- struct task_struct *t = p;
- int count = 0;
-
- p->signal->group_stop_count = 0;
-
- while_each_thread(p, t) {
- task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
- count++;
-
- /* Don't bother with already dead threads */
- if (t->exit_state)
- continue;
- sigaddset(&t->pending.signal, SIGKILL);
- signal_wake_up(t, 1);
+ task_clear_jobctl_pending(task, JOBCTL_PENDING_MASK);
+ /* Only bother with threads that might be alive */
+ if (!task->exit_state) {
+ task_set_jobctl_exiting(task, exit_code);
+ sigaddset(&task->pending.signal, SIGKILL);
+ signal_wake_up(task, 1);
}
-
- return count;
}

struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
@@ -2714,7 +2707,7 @@ bool get_signal(struct ksignal *ksig)
}

/* Has this task already been marked for death? */
- if (signal_group_exit(signal)) {
+ if (signal_group_exit(signal) || (current->jobctl & JOBCTL_TASK_EXITING)) {
ksig->info.si_signo = signr = SIGKILL;
sigdelset(&current->pending.signal, SIGKILL);
trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
@@ -2874,6 +2867,8 @@ bool get_signal(struct ksignal *ksig)
if (signal_group_exit(signal)) {
/* Another thread got here before we took the lock. */
exit_code = signal->group_exit_code;
+ } else if (current->jobctl & JOBCTL_TASK_EXITING) {
+ exit_code = current->jobctl & JOBCTL_STOP_SIGMASK;
} else {
start_group_exit_locked(signal, exit_code);
}
--
2.20.1