Messages in this thread | | | Date | Mon, 15 Oct 2018 14:05:21 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] kernel/signal: Signal-based pre-coredump notification |
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On 10/12, Enke Chen wrote: > > For simplicity and consistency, this patch provides an implementation > for signal-based fault notification prior to the coredump of a child > process. A new prctl command, PR_SET_PREDUMP_SIG, is defined that can > be used by an application to express its interest and to specify the > signal (SIGCHLD or SIGUSR1 or SIGUSR2) for such a notification. A new > signal code (si_code), CLD_PREDUMP, is also defined for SIGCHLD.
To be honest, I can't say I like this new feature...
> --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -696,6 +696,10 @@ struct task_struct { > int exit_signal; > /* The signal sent when the parent dies: */ > int pdeath_signal; > + > + /* The signal sent prior to a child's coredump: */ > + int predump_signal; > +
At least, I think predump_signal should live in signal_struct, not task_struct.
(pdeath_signal too, but it is too late to change (fix) this awkward API).
> +static void do_notify_parent_predump(struct task_struct *tsk) > +{ > + struct sighand_struct *sighand; > + struct task_struct *parent; > + struct kernel_siginfo info; > + unsigned long flags; > + int sig; > + > + parent = tsk->real_parent;
So, debuggere won't be notified, only real_parent...
> + sig = parent->predump_signal;
probably ->predump_signal should be cleared on exec?
> + /* Check again with tasklist_lock" locked by the caller */ > + if (!valid_predump_signal(sig)) > + return;
I don't understand why we need valid_predump_signal() at all.
> bool get_signal(struct ksignal *ksig) > { > struct sighand_struct *sighand = current->sighand; > @@ -2497,6 +2535,19 @@ bool get_signal(struct ksignal *ksig) > current->flags |= PF_SIGNALED; > > if (sig_kernel_coredump(signr)) { > + /* > + * Notify the parent prior to the coredump if the > + * parent is interested in such a notificaiton. > + */ > + int p_sig = current->real_parent->predump_signal; > + > + if (valid_predump_signal(p_sig)) { > + read_lock(&tasklist_lock); > + do_notify_parent_predump(current); > + read_unlock(&tasklist_lock); > + cond_resched();
perhaps this should be called by do_coredump() after coredump_wait() kills all the sub-threads?
> +static int prctl_set_predump_signal(struct task_struct *tsk, pid_t pid, int sig) > +{ > + struct task_struct *p; > + int error; > + > + /* 0 is valid for disabling the feature */ > + if (sig && !valid_predump_signal(sig)) > + return -EINVAL; > + > + /* For the current task, the common case */ > + if (pid == 0) { > + tsk->predump_signal = sig; > + return 0; > + } > + > + error = -ESRCH; > + rcu_read_lock(); > + p = find_task_by_vpid(pid); > + if (p) { > + if (!set_predump_signal_perm(p)) > + error = -EPERM; > + else { > + error = 0; > + p->predump_signal = sig; > + } > + } > + rcu_read_unlock(); > + return error; > +}
Why? I mean, why do we really want to support the pid != 0 case?
Oleg.
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