Date: Sat, 8 Sep 2012 18:14:41 +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, Andriy Gapon <avg@freebsd.org> Subject: Re: svn commit: r238907 - projects/calloutng/sys/kern Message-ID: <CAJ-FndD3xxV8gPv3czBnS-9VGXt5QV0JZDfRyvT=j8WHRA8W-w@mail.gmail.com> In-Reply-To: <20120908153839.GF33100@deviant.kiev.zoral.com.ua> References: <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> <CAJ-FndCQ6HGAfFdjofNfJ%2BHeNaE7uqoNhJB9GH4pGFxyZ_1yLg@mail.gmail.com> <5016A21B.6090409@FreeBSD.org> <CAJ-FndCFjZP=0ThpMxy6WSDQAZOm0TRkyu0bWfxVBwtT-h%2B1cA@mail.gmail.com> <5016A8E4.7070405@FreeBSD.org> <CAJ-FndB0zc-TC0E=H4p1qcOB4ngEWtwXoyhScf68G8i0p5UErw@mail.gmail.com> <CAJ-FndDAFmrEBW3d29cj-CZoPT%2BD5UPFadzL6i9BNH9ztzsJ%2BQ@mail.gmail.com> <20120908153839.GF33100@deviant.kiev.zoral.com.ua>
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On Sat, Sep 8, 2012 at 4:38 PM, Konstantin Belousov <kostikbel@gmail.com> wrote: > On Fri, Sep 07, 2012 at 11:35:15PM +0100, Attilio Rao wrote: >> On Mon, Jul 30, 2012 at 9:39 PM, Attilio Rao <attilio@freebsd.org> wrote: >> > On Mon, Jul 30, 2012 at 4:31 PM, Andriy Gapon <avg@freebsd.org> wrote: >> >> on 30/07/2012 18:04 Attilio Rao said the following: >> >>> On 7/30/12, Andriy Gapon <avg@freebsd.org> wrote: >> >>>> on 30/07/2012 17:56 Attilio Rao said the following: >> >>>>> 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. >> >>>> >> >>>> Something very tangential. I think it would also be nice to check if a >> >>>> thread has >> >>>> any(?) locks held when returning to userland. >> >>> >> >>> This happens already for INVARIANTS case, with td_locks counters. >> >>> In the !INVARIANTS case, this doesn't happen because you don't want to >> >>> add the burden to bump td_locks for the fast case and I think it is a >> >>> good approach. >> >> >> >> Ah, I missed that, thank you. >> >> BTW, it seems that td_locks is checked twice in normal syscallret() path: once in >> >> syscallret() itself and then in userret(). On this note, would it make sense to >> >> move the whole nine yards of asserts from syscallret() to userret()? >> >> I mean it might make sense to have those checks (td_critnest, td_pflags) in other >> >> paths to userland. >> > >> > Nice catch. >> > The checks were added to syscallret() in r208453. While this is fine, >> > I think that putting them in userret() may give them more exposure and >> > cover also cases like traps which are not covered right now. >> > If you want to make a patch that moves these conditions in userret() >> > I'd be in favor of it. >> >> More specifically, what do you think about this patch?: >> http://www.freebsd.org/~attilio/userret_diag.patch >> >> Of course I moved the XEN par too before the checks. >> The patch survived to few consecutive and parallel buildworlds, FWIW. > > At least in fork_return(), the last assert which checks that Giant is not > held, is no longer needed. Actually, this is unnecessary also with -CURRENT stock code today, because userret() already checks for td_locks. And it seems fork_return() is not the only function where this happens, as trap() did this too on x86 and possibly all the other architectures grew it with cut&paste. Possibly we need this further, separate, patch before userred_diag: http://www.freebsd.org/~attilio/userret_nogiant.patch > I had similar thought from the time when I added TDP_NOFAULTING check to the > syscallret(), but the loss of the syscall name in the panic output always > stopped me. I think in case of a lock/td_pinned/td_critnest/etc. leak, having the syscall number in the panic message won't change anything as you will likely need a coredump and possibly instrument your kernel with further debugging, etc. to see what's going on. Attilio -- Peace can only be achieved by understanding - A. Einstein
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