Andrew Morton <[email protected]> writes:
> On Mon, 11 Dec 2006 06:07:03 -0700
> [email protected] (Eric W. Biederman) wrote:
>
>>
>> This defers SAK so we can use the normal console semaphore to order
>> operations.
>>
>> This removes the xchg operations that I used to attempt to attmically
>> update struct pid, because of the strange locking used for SAK. With
>> SAK using the normal console semaphore nothing special is needed.
>>
>
> This is all a bit smelly.
Ok. I will take a second look, thanks for catching this.
I think I was half blind when I prepared this patch, I missed
that do_SAK was scheduling work itself.
>>
>> +void deferred_SAK(void *data)
>> +{
>> + struct vc *vc_con = data;
>> + struct vc_data *vc;
>> + struct tty_struct *tty;
>> +
>> + acquire_console_sem();
>> + vc = vc_con->d;
>> + if (vc) {
>> + tty = vc->vc_tty;
>> + /*
>> + * SAK should also work in all raw modes and reset
>> + * them properly.
>> + */
>> + if (tty)
>> + do_SAK(tty);
>> + reset_vc(vc);
>> + }
>> + release_console_sem();
>> +}
>
> And a workqueue callback which calls a function which immediately does
> another schedule_work().
>
> I suspect you can fix all of this by passing a function pointer into
> do_SAK(): to either __do_SAK or to some new function which does the vc
> lookup then calls __do_SAK().
Yes. It looks like all I need is an appropriate factor of __do_SAK() that
I can call immediately.
> It probably means that you'll need to pass some payload into the workqueue
> callback, and dhowells just went and broke that on us. That can be fixed
> by adding a new `void *tty_struct.SAK_work_data'.
>
>
> hmm, do_SAK() is being a bit bad, overwriting the ->SAK_work on a
> work_struct which might presently be scheduled. To do this safely we need
> a new variant on queue_work():
And of course there is the truly silly issue that X spells uses
Ctrl-Alt-Backspace instead of the kernel provided SAK to implement this.
Regardless that looks right. Unless there is some locking on the tty we
can exploit.
> int queue_work_with_data(struct workqueue_struct *wq,
> struct work_struct *work, void **datap, void *data
> {
> int ret = 0, cpu = get_cpu();
>
> if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
> if (datap)
> *datap = data;
> if (unlikely(is_single_threaded(wq)))
> cpu = singlethread_cpu;
> BUG_ON(!list_empty(&work->entry));
> __queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
> ret = 1;
> }
> put_cpu();
> return ret;
> }
>
> then, of course,
>
> int queue_work(struct workqueue_struct *wq, struct work_struct *work)
> {
> return queue_work_with_data(wq, work, NULL, NULL);
> }
>
> iirc, other places in the kernel need queue_work_with_data(), for removal
> of the *_WORK_NAR() stuff.
Wow. The intersection of the clean ups.
Eric
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