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SubjectRe: [BUG] ptraced process waiting on syscall may return kernel internal errnos
On 06/15, Rafael J. Wysocki wrote:
>
> +static void freeze_task(struct task_struct *p)
> +{
> if (!freezing(p)) {
> rmb();
> if (!frozen(p)) {
> set_freeze_flag(p);
> - if (p->state == TASK_STOPPED)
> - force_sig_specific(SIGSTOP, p);
> - spin_lock_irqsave(&p->sighand->siglock, flags);
> - signal_wake_up(p, p->state == TASK_STOPPED);
> - spin_unlock_irqrestore(&p->sighand->siglock, flags);
> + task_lock(p);
> + /* We don't want to send signals to kernel threads */
> + if (p->mm && !(p->flags & PF_BORROWED_MM)) {
> + task_unlock(p);
> + send_fake_signal(p);
> + } else {
> + task_unlock(p);
> + wake_up_state(p, TASK_INTERRUPTIBLE);
> + }

I don't think this is enough. Note that recalc_sigpending() checks freezing().
So a kernel thread still can get TIF_SIGPENDING if it does recalc_sigpending().

> --- linux-2.6.22-rc4-mm2.orig/include/linux/wait.h 2007-06-15 01:05:33.000000000 +0200
> +++ linux-2.6.22-rc4-mm2/include/linux/wait.h 2007-06-15 01:05:41.000000000 +0200
> @@ -240,7 +240,7 @@ do { \
> prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); \
> if (condition) \
> break; \
> - if (!signal_pending(current)) { \
> + if (!signal_pending(current) && !freezing(current)) { \
> schedule(); \
> continue; \
> } \

Personally, I think we should not modify wait_event_interruptible() and friends.
If a kernel thread wants to be frozen, it should take care about freezing()
itself.


OK, I guess I was too paranoid and you were right, it is better to ignore this
minor problem for now.

Oleg.

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