Date: Mon, 30 Jul 2012 17:59:12 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Attilio Rao <attilio@freebsd.org> 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: <20120730145912.GZ2676@deviant.kiev.zoral.com.ua> 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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--zUahwhnDqgGY+q9P Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jul 30, 2012 at 03:51:22PM +0100, Attilio Rao 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. >=20 > Yes, however I would use curthread_pflags* KPI within > THREAD_NO_SLEEPING() as this name is much more explicit. >=20 Sure, hiding it in THREAD_NO_SLEEPING (THREAD_NO_SLEEP_ENTER/LEAVE ?) is the way to use curthread_pflags_set there. As a second though, on the other hand, is it safe to modify td_flags from the interrupt context at all ? Probably yes if interrupt handler always leave td_pflags in the same state on leave as it was on entry, but couldn't too smart compiler cause inconsistent view of td_pflags inside the handler ? > > Also, I wonder, should you assert somehow that direct dispatch cannot b= lock > > as well ? >=20 > Yes, it would be optimal, but I don't think we have a flag for that > right now, do we? I am not aware of such flag, this might be a good reason to introduce it, if issue about td_pflags is just a product of my imagination. --zUahwhnDqgGY+q9P Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAlAWoUAACgkQC3+MBN1Mb4i1lwCgn/EPFLhvIMd9mjnly2r5h9hL hgAAoPaXJD8KWFJFeXMHZwo3kEFA42cH =8qAA -----END PGP SIGNATURE----- --zUahwhnDqgGY+q9P--
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