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SubjectRe: [PATCH v3] kernel/signal: Signal-based pre-coredump notification
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Hi, Oleg:

On 10/24/18 7:02 AM, Oleg Nesterov wrote:
> On 10/23, Enke Chen wrote:
>>
>> --- a/fs/coredump.c
>> +++ b/fs/coredump.c
>> @@ -590,6 +590,12 @@ void do_coredump(const kernel_siginfo_t *siginfo)
>> if (retval < 0)
>> goto fail_creds;
>>
>> + /*
>> + * Send the pre-coredump signal to the parent if requested.
>> + */
>> + do_notify_parent_predump();
>> + cond_resched();
>
> I am still not sure cond_resched() makes any sense here...
>
>> @@ -1553,6 +1553,9 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
>> tty_audit_fork(sig);
>> sched_autogroup_fork(sig);
>>
>> + /* Clear the pre-coredump signal for the child */
>> + sig->predump_signal = 0;
>
> No need, copy_signal() does zalloc().
>

Removed.

>
>> +void do_notify_parent_predump(void)
>> +{
>> + struct sighand_struct *sighand;
>> + struct kernel_siginfo info;
>> + struct task_struct *parent;
>> + unsigned long flags;
>> + int sig;
>> +
>> + read_lock(&tasklist_lock);
>> + parent = current->parent;
>> + sig = parent->signal->predump_signal;
>> + if (sig != 0) {
>> + clear_siginfo(&info);
>> + info.si_pid = task_tgid_vnr(current);
>> + info.si_signo = sig;
>> + if (sig == SIGCHLD)
>> + info.si_code = CLD_PREDUMP;
>> +
>> + sighand = parent->sighand;
>> + spin_lock_irqsave(&sighand->siglock, flags);
>> + __group_send_sig_info(sig, &info, parent);
>> + spin_unlock_irqrestore(&sighand->siglock, flags);
>
> You can just use do_send_sig_info() and remove sighand/flags/spin_lock_irqsave.

Ok.

>
> Perhaps the "likely" predump_signal==0 check at the start makes sense to avoid
> read_lock(tasklist).

I am not sure if we should/need to deviate from the convention (locking before
access the parent). In any case it may not matter as the coredump is in the
exceptional code flow.

>
> And I'd suggest to move it into coredump.c and make it static. It won't have
> another user.

Ok.

Thanks. -- Enke

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