linux-kernel - Re: please fix FUSION (Was: [v3.13][v3.14][Regression] kthread:makekthread

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Date:	Fri, 21 Mar 2014 21:31:20 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	James Bottomley <JBottomley@...allels.com>,
	Nagalakshmi.Nandigama@....com, Sreekanth.Reddy@....com,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ubuntu Kernel Team <kernel-team@...ts.ubuntu.com>,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	Tomas Henzl <thenzl@...hat.com>
Subject: Re: please fix FUSION (Was: [v3.13][v3.14][Regression]
	kthread:makekthread_create()killable)

On 03/21, Linus Torvalds wrote:
>
> On Fri, Mar 21, 2014 at 11:34 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Yes, it seems that it actually needs > 30 secs. It spends most of the time
> > (30.13286 seconds) in [..]
>
> So how about taking a completely different approach:

Due to the lack of knowledge I can not comment (or even actually
understand) your suggestion.

But it probably falls into the "right fix" category, iow "THE FIX
FROM MAINTAINERS" the temporary sigprocmask() hack should wait for.

I can't implement this by the same reason. And of course I won't
insist that we need some really stupid (and wrong) solution until
someone who understand makes the initialization asynchronous.


>  - just say that waiting for devices in the module init sequence for
> over 30 seconds is really really wrong.
>
>  - make the damn mptsas driver just register the controller from the
> init sequence, and then do device discovery asynchronously.
>
> The ATA layer does this correctly: it synchronously finds each host,
> but then it does
>
>         /* perform each probe asynchronously */
>         for (i = 0; i < host->n_ports; i++) {
>                 struct ata_port *ap = host->ports[i];
>                 async_schedule(async_port_probe, ap);
>         }
>
> and I really think SCSI drivers should do the same if they have this
> kind of "ports can take forever to probe" behavior.
>
> What would be the equivalent magic to do this for SCSI? Could we just
> make something like scsi_probe_and_add_lun() just always do this, the
> same way ata_host_register() does it?
>
>                    Linus

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