Re: [PATCH] remove name length check in a workqueue

[Andrew Morton <akpm@osdl.org>]

James Bottomley <James.Bottomley@SteelEye.com> wrote:
>
> On Wed, 2005-08-10 at 10:37 -0700, Andrew Morton wrote:
> > > and anyway, it doesn't have to be unique;
> > > set_task_comm just does a strlcpy from the name, so it will be truncated
> > > (same as for a binary with > 15 character name).
> > 
> > Yup.  But it'd be fairly silly to go adding the /%d, only to have it
> > truncated off again.
> 
> Well, but the other alternative is that we hit arbitrary BUG_ON() limits
> in systems that create numbered workqueues which is rather contrary to
> our scaleability objectives, isn't it?

Another alternative is to stop passing in such long strings ;)

> > What's the actual problem?
> 
> What I posted originally; the current SCSI format for a workqueue:
> scsi_wq_%d hits the bug after the host number rises to 100, which has
> been seen by some enterprise person with > 100 HBAs.
> 
> The reason for this name is that the error handler thread is called
> scsi_eh_%d; so we could rename all our threads to avoid this, but one
> day someone will come along with a huge enough machine to hit whatever
> limit we squeeze it down to.

OK, well scsi is using single-threaded workqueues anyway.  So we could do:

	if (singlethread)
		BUG_ON(strlen(name) > sizeof(task_struct.comm) - 1);
	else
		BUG_ON(strlen(name) > sizeof(task_struct.comm) - 1 - 4);

which gets you 10,000,000 HBAs.   Enough?

Ho hum, OK, let's just kill the BUG_ON.
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