linux-kernel - Re: 2.6.30-rc1: invalid opcode with call trace

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Date:	Thu, 9 Apr 2009 16:45:11 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Jens Axboe <jens.axboe@...cle.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Justin Madru <jdm64@...ab.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: 2.6.30-rc1: invalid opcode with call trace

On Wed, 8 Apr 2009 18:15:21 +0200,
Vegard Nossum <vegard.nossum@...il.com> wrote:

> The problem is that you have two async port probes:
> 
> [   24.177306] calling  1_async_port_probe+0x0/0xaa @ 2841
> [   24.177825] calling  2_async_port_probe+0x0/0xaa @ 2842
> 
> of which only the first completes, because the first async call itself
> tries to flush the async list while holding a lock (the
> &shost->scan_mutex in __scsi_add_device), causing deadlock.
> 
> In short, I don't think we should call async_synchronize_full() from
> scsi_complete_async_scans() at all. I'm including a more detailed
> description/justification in the patch (attached).

Not that I understand much about the scsi code, but there seem to be
two 'async' processes going on:

- async scanning of the Scsi_Host (which scsi_complete_async_scans()
  waits for)
- async execution of a part of scsi_probe (which the
  async_synchronize_full() waits for)

Considering the async scanning complete only when all probes have
finished seems sensible, so the fix doesn't look correct to me.

Would it perhaps make sense to introduce a per-Scsi_Host running list
so that do_scsi_scan_host() could use async_synchronize_domain() to
wait for all async probes for the host to finish? Or am I
misunderstanding the aim of the scsi code?
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