Date: Thu, 22 Jun 2000 08:58:40 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Bruce Evans <bde@zeta.org.au> Cc: Jason Evans <jasone@canonware.com>, Greg Lehey <grog@lemis.com>, Warner Losh <imp@village.org>, The Hermit Hacker <scrappy@hub.org>, freebsd-smp@FreeBSD.ORG Subject: Re: SP Patchset #1 up Message-ID: <200006221558.IAA03062@apollo.backplane.com> References: <Pine.BSF.4.21.0006221737130.418-100000@besplex.bde.org>
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:> :Note that the low level console drivers must not use any locks or switch
:> :context, since they need to work in debugger traps which may occur with
:> :locks in any state. Old reentrancy bugs in syscons will probably be
:> :more obvious now.
:>
:> Yah. That's why I replaced them all with mtx_enter_sched_quick(),
:> which is the closest equivalent to those requirements. The spl*()
:> calls only work if you are holding GiantMutex, and that obviously
:> is not necessarily the case for the kernel printf().
:
:You now have deadlock when the low level console i/o routines are
:reentered for ddb i/o, since task switching is either impossible or
:undesireable while ddb is active (it's essentially impossible if ddb
:was entered via a breakpoint in the middle of task switching code).
:
:When task switching is possible to avoid deadlock on console i/o
:resources, it may still be undesirable. A printf from a high priority
:interrupt task shouldn't have to wait for a printf from a low priority
:task to complete.
I don't follow. Why do I have a deadlock? This is SchedMutex I'm
talking about here, not GiantMutex.
-Matt
Matthew Dillon
<dillon@backplane.com>
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