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authorEric W. Biederman <ebiederm@xmission.com>2018-07-23 20:38:00 +0200
committerEric W. Biederman <ebiederm@xmission.com>2018-08-04 03:20:14 +0200
commit924de3b8c9410c404c6eda7abffd282b97b3ff7f (patch)
tree6bcc1ed1e1a9268ad6ce8c899d9e728e769277fb /kernel
parentfork: Skip setting TIF_SIGPENDING in ptrace_init_task (diff)
downloadlinux-924de3b8c9410c404c6eda7abffd282b97b3ff7f.tar.xz
linux-924de3b8c9410c404c6eda7abffd282b97b3ff7f.zip
fork: Have new threads join on-going signal group stops
There are only two signals that are delivered to every member of a signal group: SIGSTOP and SIGKILL. Signal delivery requires every signal appear to be delivered either before or after a clone syscall. SIGKILL terminates the clone so does not need to be considered. Which leaves only SIGSTOP that needs to be considered when creating new threads. Today in the event of a group stop TIF_SIGPENDING will get set and the fork will restart ensuring the fork syscall participates in the group stop. A fork (especially of a process with a lot of memory) is one of the most expensive system so we really only want to restart a fork when necessary. It is easy so check to see if a SIGSTOP is ongoing and have the new thread join it immediate after the clone completes. Making it appear the clone completed happened just before the SIGSTOP. The calculate_sigpending function will see the bits set in jobctl and set TIF_SIGPENDING to ensure the new task takes the slow path to userspace. V2: The call to task_join_group_stop was moved before the new task is added to the thread group list. This should not matter as sighand->siglock is held over both the addition of the threads, the call to task_join_group_stop and do_signal_stop. But the change is trivial and it is one less thing to worry about when reading the code. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/fork.c27
-rw-r--r--kernel/signal.c14
2 files changed, 29 insertions, 12 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 22d4cdb9a7ca..ab731e15a600 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1934,18 +1934,20 @@ static __latent_entropy struct task_struct *copy_process(
goto bad_fork_cancel_cgroup;
}
- /*
- * Process group and session signals need to be delivered to just the
- * parent before the fork or both the parent and the child after the
- * fork. Restart if a signal comes in before we add the new process to
- * it's process group.
- * A fatal signal pending means that current will exit, so the new
- * thread can't slip out of an OOM kill (or normal SIGKILL).
- */
- recalc_sigpending();
- if (signal_pending(current)) {
- retval = -ERESTARTNOINTR;
- goto bad_fork_cancel_cgroup;
+ if (!(clone_flags & CLONE_THREAD)) {
+ /*
+ * Process group and session signals need to be delivered to just the
+ * parent before the fork or both the parent and the child after the
+ * fork. Restart if a signal comes in before we add the new process to
+ * it's process group.
+ * A fatal signal pending means that current will exit, so the new
+ * thread can't slip out of an OOM kill (or normal SIGKILL).
+ */
+ recalc_sigpending();
+ if (signal_pending(current)) {
+ retval = -ERESTARTNOINTR;
+ goto bad_fork_cancel_cgroup;
+ }
}
@@ -1982,6 +1984,7 @@ static __latent_entropy struct task_struct *copy_process(
current->signal->nr_threads++;
atomic_inc(&current->signal->live);
atomic_inc(&current->signal->sigcnt);
+ task_join_group_stop(p);
list_add_tail_rcu(&p->thread_group,
&p->group_leader->thread_group);
list_add_tail_rcu(&p->thread_node,
diff --git a/kernel/signal.c b/kernel/signal.c
index 1e06f1eba363..9f0eafb6d474 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -373,6 +373,20 @@ static bool task_participate_group_stop(struct task_struct *task)
return false;
}
+void task_join_group_stop(struct task_struct *task)
+{
+ /* Have the new thread join an on-going signal group stop */
+ unsigned long jobctl = current->jobctl;
+ if (jobctl & JOBCTL_STOP_PENDING) {
+ struct signal_struct *sig = current->signal;
+ unsigned long signr = jobctl & JOBCTL_STOP_SIGMASK;
+ unsigned long gstop = JOBCTL_STOP_PENDING | JOBCTL_STOP_CONSUME;
+ if (task_set_jobctl_pending(task, signr | gstop)) {
+ sig->group_stop_count++;
+ }
+ }
+}
+
/*
* allocate a new signal queue record
* - this may be called without locks if and only if t == current, otherwise an