Date: Mon, 30 Jul 2012 15:56:34 +0100 From: Attilio Rao <attilio@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Davide Italiano <davide@freebsd.org>, svn-src-projects@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r238907 - projects/calloutng/sys/kern Message-ID: <CAJ-FndCQ6HGAfFdjofNfJ%2BHeNaE7uqoNhJB9GH4pGFxyZ_1yLg@mail.gmail.com> In-Reply-To: <CAJ-FndByYcZ%2BUhnkFT_n2=W=UheqUCi0%2BUAX%2BF07EqbVU=6iDQ@mail.gmail.com> References: <201207301350.q6UDobCI099069@svn.freebsd.org> <CAJ-FndBJNNBNDUEDsDBUvwoVExZpnXmoJmpY58gE3QQbw3hRGA@mail.gmail.com> <CACYV=-HmOwZ=E8Pw3-mUw0994SbvZaA3eMfcwM0fDTu_zykBJg@mail.gmail.com> <CAJ-FndBmXkyJJ=fCkEpVm84E56A2_EoM6kbch03e4RMEM6WCGQ@mail.gmail.com> <20120730143943.GY2676@deviant.kiev.zoral.com.ua> <CAJ-FndByYcZ%2BUhnkFT_n2=W=UheqUCi0%2BUAX%2BF07EqbVU=6iDQ@mail.gmail.com>
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On 7/30/12, Attilio Rao <attilio@freebsd.org> wrote: > On 7/30/12, Konstantin Belousov <kostikbel@gmail.com> wrote: >> On Mon, Jul 30, 2012 at 03:24:26PM +0100, Attilio Rao wrote: >>> On 7/30/12, Davide Italiano <davide@freebsd.org> wrote: >>> > On Mon, Jul 30, 2012 at 4:02 PM, Attilio Rao <attilio@freebsd.org> >>> > wrote: >>> > Thanks for the comment, Attilio. >>> > Yes, it's exactly what you thought. If direct flag is equal to one >>> > you're sure you're processing a callout which runs directly from >>> > hardware interrupt context. In this case, the running thread cannot >>> > sleep and it's likely you have TDP_NOSLEEPING flags set, failing the >>> > KASSERT() in THREAD_NO_SLEEPING() and leading to panic if kernel is >>> > compiled with INVARIANTS. >>> > In case you're running from SWI context (direct equals to zero) code >>> > remains the same as before. >>> > I think what I'm doing works due the assumption thread running never >>> > sleeps. Do you suggest some other way to handle this? >>> >>> Possibly the quicker way to do this is to have a way to deal with the >>> TDP_NOSLEEPING flag in recursed way, thus implement the same logic as >>> VFS_LOCK_GIANT() does, for example. >>> You will need to change the few callers of THREAD_NO_SLEEPING(), but >>> the patch should be no longer than 10/15 lines. >> >> There are already curthread_pflags_set/restore KPI designed exactly to >> handle >> nested private thread flags. > > Yes, however I would use curthread_pflags* KPI within > THREAD_NO_SLEEPING() as this name is much more explicit. > >> Also, I wonder, should you assert somehow that direct dispatch cannot >> block >> as well ? > > Yes, it would be optimal, but I don't think we have a flag for that > right now, do we? More explicitly, I think such combination TDP_NOSLEEPING + TDP_NOBLOCKING (name invented) should be set on entering the interrupt context, not only related to this part of callouts. This would be a very good help for catching buggy situations. Attilio -- Peace can only be achieved by understanding - A. Einstein
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