Re: [PATCH] Limit number of concurrent hotplug processes

[Hannes Reinecke <hare@suse.de>]

Andrew Morton wrote:
> Hannes Reinecke <hare@suse.de> wrote:
> 
>> Patch (for the semaphore version) is attached.
> 
> 
> err, what on earth is this patch trying to do?  It adds tons more
> complexity then I expected to see.  Are the async (wait=0) semantics for
> call_usermodehelper() preserved?
> 
Problem with your patch is that call_usermodehelper might block on 
down() regardless whether it is called async or sync.
So any write to sysfs which triggers a hotplug event might block until 
enough resources are available.

Most complexity is in fact due to the possibility to change khelper_max 
on the fly. If we disallow that everything else will be far cleaner.

> Why is the code now doing
> 
> 	if (stored_info.wait > 0) {
> and
> 	if (stored_info.wait >= 0) {
> 
> ?  `wait' is a boolean.  Or did its semantics get secretly changed somewhere?
> 
> Why is a new kernel thread needed to up and down a semaphore?
> 
As I said; down() might block. Unless we accept that the caller will 
only return after all down()s have been executed successfully we need 
something like that.

> Sorry, but I've completely lost the plot on what you're trying to do here!
> 
Sorry for this. I've probably pushed too hard for this.

I'll wrap up a patch which only allows for a static setting (via kernel 
command line parameters) and leave the on-the-fly setting for later :-).

> 
> I'd have though that something like the below (untested, slightly hacky)
> patch would suit.
> 
Indeed, but only if we accept that any call to call_usermodehelper might 
block if not enough resources are available.

THX for the patch, btw.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke			hare@suse.de
SuSE Linux AG				S390 & zSeries
Maxfeldstraße 5				+49 911 74053 688
90409 Nürnberg				http://www.suse.de


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