Date: Thu, 26 May 2011 12:45:29 -0400 From: Attilio Rao <attilio@freebsd.org> To: Andriy Gapon <avg@freebsd.org> Cc: Matthew Fleming <mdf@freebsd.org>, src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org>, svn-src-user@freebsd.org Subject: Re: svn commit: r222060 - in user/avg/xcpu/sys: kern sys Message-ID: <BANLkTin4pgOB1=%2BGRPJv_EPReHsf%2Bcrgfw@mail.gmail.com> In-Reply-To: <BANLkTi=m4x2H2vvn48nCv%2BT2--HfSaT2Gw@mail.gmail.com> References: <201105181508.p4IF8UoS096841@svn.freebsd.org> <20110518182441.GB2273@garage.freebsd.pl> <4DD4243C.4070301@FreeBSD.org> <BANLkTikAnB-3XbvDwGHgyqyJquH9BhqzOQ@mail.gmail.com> <4DDD13F9.5040800@FreeBSD.org> <4DDE7555.7090500@FreeBSD.org> <BANLkTi=m4x2H2vvn48nCv%2BT2--HfSaT2Gw@mail.gmail.com>
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2011/5/26 Attilio Rao <attilio@freebsd.org>: > 2011/5/26 Andriy Gapon <avg@freebsd.org>: >> on 25/05/2011 17:36 Andriy Gapon said the following: >>> on 18/05/2011 23:06 Attilio Rao said the following: >>>> However I think that TDF_INPANIC handling is not optimal. >>>> You should really acquire thread_lock otherwise you are going to break >>>> choosethread() concurrency. >>>> >>>> I would prefer to make TDF_INPANIC a private flag and just use it with >>>> curthread, if possible, but I still don't have a good way to resolve >>>> choosethread() (I would dig the runqueue adding path and resolve the >>>> problem later in the codeflow, I think). >>> >>> I've been thinking about this. >>> I think that in the new world where only one thread runs after panic we= could just >>> reduce TD_IS_INPANIC to panicstr !=3D NULL, TDF_INPANIC could be remove= d altogether >>> along with the check in =C2=A0choosethread(). =C2=A0But for some initia= l period I would like >>> to have an option to disable CPU stopping (to protect from possible bug= s, >>> regressions, etc) and for that I would like to keep TDF_INPANIC. =C2=A0= The flag could >>> be set without thread_lock() because we still allow only one thread to = be in/after >>> panic. =C2=A0But I completely agree with you that it is cleaner to move= TDF_INPANIC to >>> private flags. >>> >>> So the first step: >>> TDF_INPANIC =3D> to private flags >>> >>> Some time in the future: >>> TDF_INPANIC =3D> removed >>> TD_IS_INPANIC =3D> panicstr !=3D NULL >>> >> >> Ehm... =C2=A0After discussing this issue with you on IRC I realized absu= rdity of my >> interim suggestion. >> >> New proposal: >> #define TD_IS_INPANIC() \ >> =C2=A0 =C2=A0 =C2=A0 =C2=A0(panicstr !=3D NULL && stop_cpus_on_panic) >> >> When/if stop_cpus_on_panic knob is removed, then TD_IS_INPANIC will natu= rally be >> reduced to (panicstr !=3D NULL) and TDF_INPANIC flag will also go as we = will be >> guaranteed that the scheduler will not be running. > > Yes, that is a much better proposal. > >> Given the above, maybe TD_IS_INPANIC should change name again as it does= n't check >> properties of a particular thread, but rather the whole system state? = =C2=A0Also, >> sys/proc.h doesn't seem like the best location for it anymore. > > Yes, I think it would be better something like SYSTEM_IN_PANIC() or such. > The natural location for this would be kern_shutdown.c but it really > doesn't have a corresponding header (maybe sys/reboot.h could be, with > some more lifting, but for the moment, no), thus you can still pickup > something easy to use like proc.h or systm.h. I think that systm.h may be the best place as long as it is where panic() is declared. Attilio --=20 Peace can only be achieved by understanding - A. Einstein
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