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authorOleg Nesterov <oleg@tv-sign.ru>2006-03-28 16:11:26 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-28 18:36:44 -0800
commit4a2c7a7837da1b91468e50426066d988050e4d56 (patch)
treee7e321e1a61b934e3c0d938360cc4b990407fcea /kernel
parent47e65328a7b1cdfc4e3102e50d60faf94ebba7d3 (diff)
[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 <oleg@tv-sign.ru> Acked-By: Eric Biederman <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/fork.c37
1 files changed, 17 insertions, 20 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index bc551efb5fd4..aa50c848fae7 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(&current->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(&current->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(&current->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,