> Subject: Re: [RFC] [PATCH] selective signal ptracing
> From: Oleg Nesterov <[email protected]>
> Date: Sat, 16 Jun 2007 13:24:15 +0400
> To: John Blackwood <[email protected]>
> CC: Alan Cox <[email protected]>, Roland McGrath
<[email protected]>, [email protected]
>
> John Blackwood wrote:
> > >
> > > By default all signals are ptraced as before. However, a debugger
> > > may now modify the set of per-task ptraced signals, where only the
> > > signals in this ptrace signal mask will be ptraced.
>
> I must admit, I agree with Roland...
>
> > > +void ptrace_update_traced_signals(struct task_struct *child,
> > > + sigset_t *new_smaskp)
> > > +{
> > > [...snip...]
> > > +
> > > + spin_lock_irqsave(&child->sighand->siglock, flags);
> > > +
> > > + if (child->sighand == NULL) {
>
> How so?
>
> Oleg.
Hi Oleg.
Right, this above is not a good check for a NULL sighand.
Possibly, this routine could use something like the
rcu_read_lock()/lock_task_sighand() sequences used elsewhere
(shown below).
The whole ptrace_update_traced_signals() where we drain ignored signals
is not dealt with today by ptraced tasks when the debugger exits or
detaches from a target task. So this whole routine is not entirely
related just to selective signal ptracing.
Thanks for you input.
diff -rup linux-2.6.22-rc4-git5.old/kernel/exit.c
linux-2.6.22-rc4-git5.new/kernel/exit.c
--- linux-2.6.22-rc4-git5.old/kernel/exit.c 2007-06-18
14:36:09.000000000 -0400
+++ linux-2.6.22-rc4-git5.new/kernel/exit.c 2007-06-18
14:31:16.000000000 -0400
+/*
+ * void ptrace_update_traced_signals(
+ * struct task_struct *child, sigset_t *new_smaskp)
+ *
+ * Update the signal mask of ptraced signals, removing any ignored
+ * pending signals that are no longer ptraced. 'new_smaskp' points
+ * to the new ptrace signal mask which will be stored into
+ * child->ptrace_sigmask.
+ */
+void ptrace_update_traced_signals(struct task_struct *child,
+ sigset_t *new_smaskp)
+{
+ int sig = 0, index = 0;
+ unsigned long int flags;
+ sigset_t prev_smask;
+
+ /* Get signals that were previously, but no longer ptraced. */
+ signandsets(&prev_smask, &child->ptrace_sigmask, new_smaskp);
+ child->ptrace_sigmask = *new_smaskp;
+ rcu_read_lock();
+ while (!sigisemptyset(&prev_smask)) {
+ while (index < _NSIG_WORDS) {
+ if (prev_smask.sig[index]) {
+ sig = ffz(~prev_smask.sig[index]) +
+ (index * _NSIG_BPW) + 1;
+ break;
+ }
+ index++;
+ }
+ /* Remove signal from the previously ptraced signal mask. */
+ sigdelset(&prev_smask, sig);
+
+ if (!lock_task_sighand(child, &flags)) {
+ /* This task is exiting, so just return. */
+ unlock_task_sighand(child, &flags);
+ rcu_read_unlock();
+ return;
+ }
+ if (!sig_ignored(child, sig)) {
+ unlock_task_sighand(child, &flags);
+ continue;
+ }
+ /* Remove any queued signals - they should now be ignored. */
+ rm_from_queue(sigmask(sig), &child->pending);
+ rm_from_queue(sigmask(sig), &child->signal->shared_pending);
+ unlock_task_sighand(child, &flags);
+ }
+ rcu_read_unlock();
+}
-
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