From 4a2c7a7837da1b91468e50426066d988050e4d56 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 28 Mar 2006 16:11:26 -0800 Subject: [PATCH] [PATCH] make fork() atomic wrt pgrp/session signals Eric W. Biederman wrote: > > Ok. SUSV3/Posix is clear, fork is atomic with respect > to signals. Either a signal comes before or after a > fork but not during. (See the rationale section). > http://www.opengroup.org/onlinepubs/000095399/functions/fork.html > > The tasklist_lock does not stop forks from adding to a process > group. The forks stall while the tasklist_lock is held, but a fork > that began before we grabbed the tasklist_lock simply completes > afterwards, and the child does not receive the signal. This also means that SIGSTOP or sig_kernel_coredump() signal can't be delivered to pgrp/session reliably. With this patch copy_process() returns -ERESTARTNOINTR when it detects a pending signal, fork() will be restarted transparently after handling the signals. This patch also deletes now unneeded "group_stop_count > 0" check, copy_process() can no longer succeed while group stop in progress. Signed-off-by: Oleg Nesterov Acked-By: Eric Biederman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 37 +++++++++++++++++-------------------- 1 file changed, 17 insertions(+), 20 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index bc551efb5fd..aa50c848fae 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1136,16 +1136,6 @@ static task_t *copy_process(unsigned long clone_flags, !cpu_online(task_cpu(p)))) set_task_cpu(p, smp_processor_id()); - /* - * Check for pending SIGKILL! The new thread should not be allowed - * to slip out of an OOM kill. (or normal SIGKILL.) - */ - if (sigismember(¤t->pending.signal, SIGKILL)) { - write_unlock_irq(&tasklist_lock); - retval = -EINTR; - goto bad_fork_cleanup_namespace; - } - /* CLONE_PARENT re-uses the old parent */ if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) p->real_parent = current->real_parent; @@ -1154,6 +1144,23 @@ static task_t *copy_process(unsigned long clone_flags, p->parent = p->real_parent; spin_lock(¤t->sighand->siglock); + + /* + * 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)) { + spin_unlock(¤t->sighand->siglock); + write_unlock_irq(&tasklist_lock); + retval = -ERESTARTNOINTR; + goto bad_fork_cleanup_namespace; + } + if (clone_flags & CLONE_THREAD) { /* * Important: if an exit-all has been started then @@ -1170,16 +1177,6 @@ static task_t *copy_process(unsigned long clone_flags, p->group_leader = current->group_leader; list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group); - if (current->signal->group_stop_count > 0) { - /* - * There is an all-stop in progress for the group. - * We ourselves will stop as soon as we check signals. - * Make the new thread part of that group stop too. - */ - current->signal->group_stop_count++; - set_tsk_thread_flag(p, TIF_SIGPENDING); - } - if (!cputime_eq(current->signal->it_virt_expires, cputime_zero) || !cputime_eq(current->signal->it_prof_expires, -- 2.20.1