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exec: rework the group exit and fix the race with kill

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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 <oleg@tv-sign.ru>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Robin Holt <holt@sgi.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2008-02-04 22:27:24 -08:00 committed by Linus Torvalds
parent f558b7e408
commit ed5d2cac11
4 changed files with 15 additions and 12 deletions
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13
fs/exec.c
View file

@ -760,7 +760,7 @@ static int de_thread(struct task_struct *tsk)
*/
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.
@ -778,6 +778,7 @@ static int de_thread(struct task_struct *tsk)
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);
@ -802,7 +803,6 @@ static int de_thread(struct task_struct *tsk)
}
sig->notify_count = count;
sig->group_exit_task = tsk;
while (atomic_read(&sig->count) > count) {
__set_current_state(TASK_UNINTERRUPTIBLE);
spin_unlock_irq(lock);
@ -871,15 +871,10 @@ static int de_thread(struct task_struct *tsk)
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);
@ -1549,7 +1544,7 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
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;

7
include/linux/sched.h
View file

@ -555,6 +555,13 @@ 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..
*/

3
kernel/exit.c
View file

@ -1083,11 +1083,12 @@ 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);

4
kernel/signal.c
View file

@ -957,7 +957,6 @@ void zap_other_threads(struct task_struct *p)
{
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)) {
@ -1697,7 +1696,8 @@ 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.