Date: Mon, 24 Sep 2007 12:28:33 -0400 From: John Baldwin <jhb@freebsd.org> To: Nate Lawson <nate@root.org> Cc: freebsd-acpi@freebsd.org, freebsd-current@freebsd.org, Jung-uk Kim <jkim@freebsd.org> Subject: Re: [PATCH] OsdSynch.c modernization Message-ID: <200709241228.34162.jhb@freebsd.org> In-Reply-To: <46F7E19B.3010603@root.org> References: <200709181516.11207.jkim@FreeBSD.org> <200709241155.56926.jhb@freebsd.org> <46F7E19B.3010603@root.org>
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On Monday 24 September 2007 12:11:07 pm Nate Lawson wrote: > 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. Disabling interrupts and then calling malloc() is wrong however. -- John Baldwin
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