Re: [PATCH v3] kernel/signal: Signal-based pre-coredump notification

[Enke Chen <enkechen@cisco.com>]

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