Re: [patch V4 2/2] signal: Allow tasks to cache one sigqueue struct

[Thomas Gleixner <tglx@linutronix.de>]

On Tue, Mar 23 2021 at 19:04, Oleg Nesterov wrote:
> On 03/22, Thomas Gleixner wrote:
>> +static void sigqueue_cache_or_free(struct sigqueue *q, bool cache)
>> +	if (q) {
>> +		tsk->sigqueue_cache = NULL;
>> +		/* If task is self reaping, don't cache it back */
>> +		sigqueue_cache_or_free(q, tsk != current);
>                                           ^^^^^^^^^^^^^^
> Still not right or I am totally confused.
>
> tsk != current can be true if an exiting (and autoreaping) sub-thread
> releases its group leader.
>
> IOW. Suppose a process has 2 threads, its parent ignores SIGCHLD.
>
> The group leader L exits. Then its sub-thread T exits too and calls
> release_task(T). In this case the tsk != current is false.
>
> But after that T calls release_task(L) and L != T is true.

Bah. yes.

> I'd suggest to free tsk->sigqueue_cache in __exit_signal() unconditionally and
> remove the "bool cache" argument from sigqueue_cache_or_free().

That's what you get from trying to be clever, dammit.

Thanks for walking me through the oddities of exit !

       tglx