Date: Mon, 24 Sep 2007 10:03:18 -0700 From: Nate Lawson <nate@root.org> To: Jung-uk Kim <jkim@FreeBSD.org> Cc: freebsd-acpi@FreeBSD.org, freebsd-current@FreeBSD.org, John Baldwin <jhb@FreeBSD.org> Subject: Re: [PATCH] OsdSynch.c modernization Message-ID: <46F7EDD6.4010508@root.org> In-Reply-To: <200709241259.01518.jkim@FreeBSD.org> References: <200709181516.11207.jkim@FreeBSD.org> <46F7E19B.3010603@root.org> <200709241228.34162.jhb@freebsd.org> <200709241259.01518.jkim@FreeBSD.org>
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Jung-uk Kim wrote: > On Monday 24 September 2007 12:28 pm, John Baldwin wrote: >> 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. > > Understood. As I said earlier, I really like to fix it correctly. > > <rant> > However, the problem is that there are so many different BIOSes out > there, taking so different code paths. Whenever I thought it's > fixed, someone says 'you broke my laptop' or 'FreeBSD is bad because > it doesn't boot on my laptop but Linux and Windows boot fine'. :-( > </rant> > > (At least on my laptop) I found the malloc() was called from our code, > i.e., AcpiOsExecute() from OsdSched.c. I'll try something shortly > cause I was going to rewrite the file anyway. Yep, that's because we need a task structure that's different for each call and acpi-ca doesn't like the "pending" argument (see OsdSchedule.c). One fix for this is to just use a hack and cast the fn to discard the extra arg. Not sure this would work. I thought malloc(...NOWAIT) *could* be called with a mutex held? It just checks a list and returns NULL if empty, right? -- Nate
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