Date: Wed, 29 Nov 2017 19:36:52 +0100 From: "Hartmann, O." <ohartmann@walstatt.org> To: Justin Hibbits <jrh29@alumni.cwru.edu> Cc: Konstantin Belousov <kostikbel@gmail.com>, Hans Petter Selasky <hps@selasky.org>, src-committers <src-committers@freebsd.org>, John Baldwin <jhb@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, KrishnamRaju ErapaRaju <Krishna2@chelsio.com>, Konstantin Belousov <kib@freebsd.org>, Nathan Whitehorn <nwhitehorn@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "O. Hartmann" <ohartmann@walstatt.org> Subject: Re: svn commit: r326218 - head/sys/kern Message-ID: <20171129193647.77859f62@hermann> In-Reply-To: <CAHSQbTAfQcudcVRUGR=wwm9hvbgvhaFuTVjA8D15C%2B8fRfN=hw@mail.gmail.com> References: <201711252341.vAPNf5Qx001464@repo.freebsd.org> <14322447.103fKFTi3y@ralph.baldwin.cx> <3fc45d5f-22b9-0562-278b-c515e36f48e7@freebsd.org> <14058479.lc6xlYgyBM@ralph.baldwin.cx> <2e752d6a-d34a-dde0-acea-fdbf8bebea51@selasky.org> <20171129161356.GA2272@kib.kiev.ua> <CAHSQbTAfQcudcVRUGR=wwm9hvbgvhaFuTVjA8D15C%2B8fRfN=hw@mail.gmail.com>
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On Wed, 29 Nov 2017 10:59:34 -0600 Justin Hibbits <jrh29@alumni.cwru.edu> wrote: > On Wed, Nov 29, 2017 at 10:13 AM, Konstantin Belousov > <kostikbel@gmail.com> wrote: > > On Wed, Nov 29, 2017 at 04:33:50PM +0100, Hans Petter Selasky > > wrote: > >> Hi Nathan, > >> > >> The chunk below causes sched_pin() to stop working and should be > >> removed from your commit ??!! > >> > >> It probably explains the hangs seen recently reported by various > >> brave people running 12-current :-) > >> > >> Specifically I see threads migrating between CPUs when > >> td->td_pinned > 0 using the LinuxKPI RCU API, which in turn leads > >> to a hang when trying to synchronize RCU. > >> > >> --HPS > >> > >> diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c > >> index 5c8bae5afa1..bd4b505f6c3 100644 > >> --- a/sys/kern/sched_ule.c > >> +++ b/sys/kern/sched_ule.c > >> @@ -2453,7 +2453,7 @@ sched_add(struct thread *td, int flags) > >> * Pick the destination cpu and if it isn't ours transfer > >> to the > >> * target cpu. > >> */ > >> - td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid > >> to start */ > >> +// td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid > >> to start */ > >> cpu = sched_pickcpu(td, flags); > >> tdq = sched_setcpu(td, cpu, flags); > >> tdq_add(tdq, td, flags); > > > > To clarify. It seems that this change breaks sched_bind(). > > > > It might be that LinuxKPI does use sched_pin() in somewhat > > questionable way. Namely, the code puts the thread off the CPU > > (e.g. by taking a lock). Then, is it guaranteed that the pinned > > thread returns to the same cpu after sched_add() ? > > > > I think that the second behaviour is not guaranteed, but it might > > happens by the way the things are arranged. If guaranteed, then the > > sched_pin() breakage is same as for sched_bind(). > > > > I see the same breakage on PowerPC with the dtsec(4) driver, which > pins interrupts to CPUs, now causing interrupts to migrate to cores > without the matching portal mapping. > > - Justin > _______________________________________________ > svn-src-head@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/svn-src-head > To unsubscribe, send any mail to > "svn-src-head-unsubscribe@freebsd.org" I can not understand why this untested patch isn't reverted already. It brings down any system I have at hand within short time and if someone is stupid enough - like me - performing an installworld while new kernel already has been installed, the old binaries, one day old, seem to be incompatible and BTX immediately bails out. I brought down the fourth box - by intention and the problem is serious and can be reproduced easily.
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