Re: libata total system lockup fix

[Tejun Heo <htejun@gmail.com>]

  Hi, Mark.

Mark Lord wrote:
> After a week of further experience with this patch,
> I regretfully inform one and all that it does not
> entirely fix the lockups.
> 
> My system has experienced three of them during the
> past 24 hours.. after many days without.

  Oh.. crap.

> I'm now reverting to the original "broken" patch
> that keeps my system alive.
> 
> Cheers!

  I've been trying to reproduce your lockup here, but haven't succeeded 
yet.  I'm currently doing multiple "while true; do cat /dev/sr0; done", 
bonnie, raw random IOs (latter two are to give some randomness to test 
condition).

  I'm also digging code to discover how exactly the lockup loop occurs. 
  My lockup was between scsi_softirq and scsi_eh_scmd_add (EIP jumped 
between the two functions), and I orginally assumed adding eh_entry to 
corrupt eh_cmd_q screwed local_q iteration in scsi_softirq.  And as 
clearing eh_cmd_q solved my problem, I didn't look into it further.

  If possible, can you please hook up your notebook to a serial console 
and, when lockup occurs (with or without INIT_LIST_HEAD one liner), dump 
call trace by ctrl-alt-sysrq-p multiple times (10times across 5secs 
should do, I think) to verify that we're looking at the same problem? 
It would be best if I can find a way to reproduce it here, but the busy 
loop has been running for two hours now and nothing happened.  :-(

  Thanks.

-- 
tejun