As Roland pointed out, we have the very old problem with exec. de_thread() sets
SIGNAL_GROUP_EXIT, kills other threads, changes ->group_leader and then clears
signal->flags. All signals (even fatal ones) sent in this window (which is not
too small) will be lost.
With this patch exec doesn't abuse SIGNAL_GROUP_EXIT. signal_group_exit(), the
new helper, should be used to detect exit_group() or exec() in progress. It can
have more users, but this patch does only strictly necessary changes.
Signed-off-by: Oleg Nesterov <[email protected]>
include/linux/sched.h | 7 +++++++
fs/exec.c | 13 ++++---------
kernel/signal.c | 4 ++--
kernel/exit.c | 3 ++-
4 files changed, 15 insertions(+), 12 deletions(-)
--- PT/include/linux/sched.h~2_EXIT_KILL 2007-11-26 16:47:35.000000000 +0300
+++ PT/include/linux/sched.h 2007-12-02 14:53:29.000000000 +0300
@@ -540,6 +540,13 @@ struct signal_struct {
#define SIGNAL_STOP_CONTINUED 0x00000004 /* SIGCONT since WCONTINUED reap */
#define SIGNAL_GROUP_EXIT 0x00000008 /* group exit in progress */
+/* If true, all threads except ->group_exit_task have pending SIGKILL */
+static inline int signal_group_exit(const struct signal_struct *sig)
+{
+ return (sig->flags & SIGNAL_GROUP_EXIT) ||
+ (sig->group_exit_task != NULL);
+}
+
/*
* Some day this will be a full-fledged user tracking system..
*/
--- PT/fs/exec.c~2_EXIT_KILL 2007-11-20 17:16:09.000000000 +0300
+++ PT/fs/exec.c 2007-12-02 16:07:22.000000000 +0300
@@ -759,7 +759,7 @@ static int de_thread(struct task_struct
*/
read_lock(&tasklist_lock);
spin_lock_irq(lock);
- if (sig->flags & SIGNAL_GROUP_EXIT) {
+ if (signal_group_exit(sig)) {
/*
* Another group action in progress, just
* return so that the signal is processed.
@@ -777,6 +777,7 @@ static int de_thread(struct task_struct
if (unlikely(tsk->group_leader == task_child_reaper(tsk)))
task_active_pid_ns(tsk)->child_reaper = tsk;
+ sig->group_exit_task = tsk;
zap_other_threads(tsk);
read_unlock(&tasklist_lock);
@@ -801,7 +802,6 @@ static int de_thread(struct task_struct
}
sig->notify_count = count;
- sig->group_exit_task = tsk;
while (atomic_read(&sig->count) > count) {
__set_current_state(TASK_UNINTERRUPTIBLE);
spin_unlock_irq(lock);
@@ -870,15 +870,10 @@ static int de_thread(struct task_struct
leader->exit_state = EXIT_DEAD;
write_unlock_irq(&tasklist_lock);
- }
+ }
sig->group_exit_task = NULL;
sig->notify_count = 0;
- /*
- * There may be one thread left which is just exiting,
- * but it's safe to stop telling the group to kill themselves.
- */
- sig->flags = 0;
no_thread_group:
exit_itimers(sig);
@@ -1548,7 +1543,7 @@ static inline int zap_threads(struct tas
int err = -EAGAIN;
spin_lock_irq(&tsk->sighand->siglock);
- if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT)) {
+ if (!signal_group_exit(tsk->signal)) {
tsk->signal->group_exit_code = exit_code;
zap_process(tsk);
err = 0;
--- PT/kernel/signal.c~2_EXIT_KILL 2007-12-02 16:56:16.000000000 +0300
+++ PT/kernel/signal.c 2007-12-02 17:05:15.000000000 +0300
@@ -957,7 +957,6 @@ void zap_other_threads(struct task_struc
{
struct task_struct *t;
- p->signal->flags = SIGNAL_GROUP_EXIT;
p->signal->group_stop_count = 0;
for (t = next_thread(p); t != p; t = next_thread(t)) {
@@ -1692,7 +1691,8 @@ static int do_signal_stop(int signr)
} else {
struct task_struct *t;
- if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED))
+ if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||
+ unlikely(sig->group_exit_task))
return 0;
/*
* There is no group stop already in progress.
--- PT/kernel/exit.c~2_EXIT_KILL 2007-12-02 14:36:22.000000000 +0300
+++ PT/kernel/exit.c 2007-12-02 15:53:35.000000000 +0300
@@ -1081,11 +1081,12 @@ do_group_exit(int exit_code)
struct signal_struct *const sig = current->signal;
struct sighand_struct *const sighand = current->sighand;
spin_lock_irq(&sighand->siglock);
- if (sig->flags & SIGNAL_GROUP_EXIT)
+ if (signal_group_exit(sig))
/* Another thread got here before we took the lock. */
exit_code = sig->group_exit_code;
else {
sig->group_exit_code = exit_code;
+ sig->flags = SIGNAL_GROUP_EXIT;
zap_other_threads(current);
}
spin_unlock_irq(&sighand->siglock);
--
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