Date: Mon, 24 Sep 2007 09:11:07 -0700 From: Nate Lawson <nate@root.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-acpi@freebsd.org, freebsd-current@freebsd.org, Jung-uk Kim <jkim@freebsd.org> Subject: Re: [PATCH] OsdSynch.c modernization Message-ID: <46F7E19B.3010603@root.org> In-Reply-To: <200709241155.56926.jhb@freebsd.org> References: <200709181516.11207.jkim@FreeBSD.org> <200709211827.29763.jkim@FreeBSD.org> <3bbf2fe10709240237u790de351wddb81b0c511d7435@mail.gmail.com> <200709241155.56926.jhb@freebsd.org>
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John Baldwin wrote: > 2007/9/22, Jung-uk Kim <jkim@freebsd.org>: >> I thought exactly the same when I started rewriting it (almost half >> year ago!). I have tried all of the above, spent numerous sleepless >> nights, and miserably failed. :-( >> >> Spin mutex is too restrictive (e.g., it cannot be used with other >> locks gracefully). critical_enter() causes: >> >> panic: blockable sleep lock (sleep mutex) 32 @ >> /usr/src/sys/vm/uma_core.c:1830 cpuid = 0 >> KDB: enter: panic >> [thread pid 21 tid 100013 ] >> Stopped at kdb_enter+0x32: leave > > However, disabling interrupts while you block on other locks is just as bad, > we just don't assert for it. Better would be to fix ACPI-CA to not try to > malloc() while holding a spin lock. You should be able to see where it is > doing that via the stack trace. If the malloc is using M_NOWAIT you will be > far better off using a plain mutex and just not disabling interrupts. For 7.0, we're going with what we have (sx locks) since it's well-tested and not wrong, maybe just less than optimal. Remember that acpi locks are acquired a few dozen times every 10 seconds or so, so this is not at risk of being a performance issue. I think it's a good idea to work with Bob Moore to improve things on their side as well. Then we can revisit this and clean it up. -- Nate
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