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From: John Baldwin <jhb@freebsd.org>
To: freebsd-current@freebsd.org
Subject: Re: ipmi patch for review
Date: Thu, 19 Sep 2013 15:04:46 -0400
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 (bigwig.baldwin.cx); Thu, 19 Sep 2013 16:26:21 -0400 (EDT)
Cc: Gleb Smirnoff <glebius@freebsd.org>
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On Tuesday, September 17, 2013 6:21:10 am Gleb Smirnoff wrote:
>   Hi!
> 
>   When system is writing a kernel core dump, it issues watchdog
> pat wdog_kern_pat(WD_LASTVAL). If ipmi is in action, it registers
> ipmi_wd_event() as event for watchdog. Thus ipmi_wd_event() is
> called in dumping context.
> 
> The problem is that ipmi_wd_event() calls into ipmi_set_watchdog(),
> that calls into ipmi_alloc_request(), which uses M_WAITOK and
> thus sleeps. This is a smaller problem, since can be converted to
> M_NOWAIT. But ipmi_set_watchdog() then calls into
> ipmi_submit_driver_request(), which calls msleep() any time.
> 
>   The attached patch allows me to successfully write cores in
> presence of IPMI.

Of course, the watchdog might go off during your dump. :)

The real fix is more complicated, which is that we should not use
a worker thread for at least SMIC and KCS.

-- 
John Baldwin