Date: Wed, 28 Dec 2016 19:25:22 +0100 From: Vincenzo Maffione <v.maffione@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Luigi Rizzo <rizzo@iet.unipi.it>, Adrian Chadd <adrian.chadd@gmail.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it>, Luigi Rizzo <luigi@freebsd.org>, Navdeep Parhar <np@freebsd.org> Subject: Re: cxgbe's native netmap support broken since r307394 Message-ID: <CA%2B_eA9jqPHD9zmBqurYtwefgK=ZG51=9bU%2B7ovZtmJK=ze1tnA@mail.gmail.com> In-Reply-To: <2698793.0b4KyHrqck@ralph.baldwin.cx> References: <20161217222812.GA4979@ox> <CAJ-VmomTTPfr85E1CqbYZ2dj1R7ZPkTFP03Z-AAd_u=5GjNb4g@mail.gmail.com> <CA%2BhQ2%2BjBJXs2gGQaiJVEkFQx=qiecQ=P637epvtex9XcnXzBEQ@mail.gmail.com> <2698793.0b4KyHrqck@ralph.baldwin.cx>
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Hi, The "worker_lock" is taken by nm_os_kthread_wakeup_worker(), which in turn is called by nm_pt_host_notify(). The latter function is a callback that may be called by a driver interrupt service routine; more precisely this happens when the driver calls netmap_tx_irq() or netmap_rx_irq(). As far as I know in FreeBSD it is not possible to lock a MTX_DEF mtx inside an ISR. Am I wrong on this? Cheers, Vincenzo 2016-12-28 19:06 GMT+01:00 John Baldwin <jhb@freebsd.org>: > Why are you using MTX_SPIN? Changing the lock type to MTX_DEF would seem to > be a smaller patch and probably more correct for FreeBSD. > > On Thursday, December 22, 2016 05:29:41 PM Luigi Rizzo wrote: >> sure go ahead and thank you! >> >> On Thu, Dec 22, 2016 at 5:15 PM, Adrian Chadd <adrian.chadd@gmail.com> wrote: >> > ok, does anyone mind if I commit it as-is? >> > >> > >> > -a >> > >> > >> > On 21 December 2016 at 13:37, Vincenzo Maffione <v.maffione@gmail.com> wrote: >> >> Hi Luigi, >> >> I attached a minimal change containing two fixes: >> >> >> >> - change IFNET_WLOCK into IFNET_RLOCK, to fix the cxgbe issue related >> >> to this thread >> >> - use the proper locking functions for the "worker_lock", unrelated >> >> but needed to avoid the O.S. to trap because of a mismatch between >> >> MTX_SPIN and MTX_DEF. >> >> >> >> Cheers, >> >> Vincenzo >> >> >> >> 2016-12-21 20:30 GMT+01:00 Luigi Rizzo <rizzo@iet.unipi.it>: >> >>> On Wed, Dec 21, 2016 at 11:15 AM, Vincenzo Maffione >> >>> <v.maffione@gmail.com> wrote: >> >>>> Hi, >> >>>> There is no commit related to that in the FreeBSD svn or git. >> >>>> >> >>>> The fix has been published to the github netmap repository here >> >>>> (branch master): https://github.com/luigirizzo/netmap >> >>>> >> >>>> What we should do is to import all the recent updates from the github >> >>>> into HEAD. I can prepare a patch for HEAD, if you wish. Just let me >> >>>> know. >> >>> >> >>> I just checked and the diff between FreeBSD head and netmap head >> >>> in github is almost 3k lines due to a lot of recent refactoring. >> >>> So, if there is an easy way to extract just the locking change that would >> >>> be preferable as an interim solution. >> >>> >> >>> cheers >> >>> luigi >> >>> >> >>>> >> >>>> Cheers, >> >>>> Vincenzo >> >>>> >> >>>> >> >>>> 2016-12-20 21:45 GMT+01:00 Adrian Chadd <adrian.chadd@gmail.com>: >> >>>>> hi, >> >>>>> >> >>>>> What's the commit? We should get it into -HEAD asap. >> >>>>> >> >>>>> >> >>>>> -adrian >> >>>>> >> >>>>> >> >>>>> On 20 December 2016 at 01:25, Vincenzo Maffione <v.maffione@gmail.com> wrote: >> >>>>>> Ok, applied to the netmap github repo. >> >>>>>> This fix will be published when Luigi does the next commit on FreeBSD. >> >>>>>> >> >>>>>> Cheers, >> >>>>>> Vincenzo >> >>>>>> >> >>>>>> 2016-12-19 20:05 GMT+01:00 Navdeep Parhar <np@freebsd.org>: >> >>>>>>> IFNET_RLOCK will work, thanks. >> >>>>>>> >> >>>>>>> Navdeep >> >>>>>>> >> >>>>>>> On Mon, Dec 19, 2016 at 3:21 AM, Vincenzo Maffione <v.maffione@gmail.com> wrote: >> >>>>>>>> Hi Navdeep, >> >>>>>>>> >> >>>>>>>> Indeed, we have reviewed the code, and we think it is ok to >> >>>>>>>> implement nm_os_ifnet_lock() with IFNET_RLOCK(), instead of using >> >>>>>>>> IFNET_WLOCK(). >> >>>>>>>> Since IFNET_RLOCK() results into sx_slock(), this should fix the issue. >> >>>>>>>> >> >>>>>>>> On FreeBSD, this locking is needed to protect a flag read by nm_iszombie(). >> >>>>>>>> However, on Linux the same lock is also needed to protect the call to >> >>>>>>>> the nm_hw_register() callback, so we prefer to have an "unified" >> >>>>>>>> locking scheme, i.e. always calling nm_hw_register under the lock. >> >>>>>>>> >> >>>>>>>> Does this make sense to you? Would it be easy for you to make a quick >> >>>>>>>> test by replacing IFNET_WLOCK with IFNET_RLOCK? >> >>>>>>>> >> >>>>>>>> Thanks, >> >>>>>>>> Vincenzo >> >>>>>>>> >> >>>>>>>> 2016-12-17 23:28 GMT+01:00 Navdeep Parhar <np@freebsd.org>: >> >>>>>>>>> Luigi, Vincenzo, >> >>>>>>>>> >> >>>>>>>>> The last major update to netmap (r307394 and followups) broke cxgbe's >> >>>>>>>>> native netmap support. The problem is that netmap_hw_reg now holds an >> >>>>>>>>> rw_lock around the driver's netmap_on/off routines. It has always been >> >>>>>>>>> safe for the driver to sleep during these operations but now it panics >> >>>>>>>>> instead. >> >>>>>>>>> >> >>>>>>>>> Why is IFNET_WLOCK needed here? It seems like a regression to disallow >> >>>>>>>>> sleep on the control path. >> >>>>>>>>> >> >>>>>>>>> Regards, >> >>>>>>>>> Navdeep >> >>>>>>>>> >> >>>>>>>>> begin_synchronized_op with the following non-sleepable locks held: >> >>>>>>>>> exclusive rw ifnet_rw (ifnet_rw) r = 0 (0xffffffff8271d680) locked @ >> >>>>>>>>> /root/ws/head/sys/dev/netmap/netmap_freebsd.c:95 >> >>>>>>>>> stack backtrace: >> >>>>>>>>> #0 0xffffffff810837a5 at witness_debugger+0xe5 >> >>>>>>>>> #1 0xffffffff81084d88 at witness_warn+0x3b8 >> >>>>>>>>> #2 0xffffffff83ef2bcc at begin_synchronized_op+0x6c >> >>>>>>>>> #3 0xffffffff83f14beb at cxgbe_netmap_reg+0x5b >> >>>>>>>>> #4 0xffffffff809846f1 at netmap_hw_reg+0x81 >> >>>>>>>>> #5 0xffffffff809806de at netmap_do_regif+0x19e >> >>>>>>>>> #6 0xffffffff8098121d at netmap_ioctl+0x7ad >> >>>>>>>>> #7 0xffffffff8098682f at freebsd_netmap_ioctl+0x5f >> >>>>>>>> >> >>>>>>>> >> >>>>>>>> >> >>>>>>>> -- >> >>>>>>>> Vincenzo Maffione >> >>>>>>>> _______________________________________________ >> >>>>>>>> freebsd-net@freebsd.org mailing list >> >>>>>>>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >> >>>>>>>> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> -- >> >>>>>> Vincenzo Maffione >> >>>>>> _______________________________________________ >> >>>>>> freebsd-net@freebsd.org mailing list >> >>>>>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >> >>>>>> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >> >>>> >> >>>> >> >>>> >> >>>> -- >> >>>> Vincenzo Maffione >> >>> >> >>> >> >>> >> >>> -- >> >>> -----------------------------------------+------------------------------- >> >>> Prof. Luigi RIZZO, rizzo@iet.unipi.it . Dip. di Ing. dell'Informazione >> >>> http://www.iet.unipi.it/~luigi/ . Universita` di Pisa >> >>> TEL +39-050-2217533 . via Diotisalvi 2 >> >>> Mobile +39-338-6809875 . 56122 PISA (Italy) >> >>> -----------------------------------------+------------------------------- >> >> >> >> >> >> >> >> -- >> >> Vincenzo Maffione >> >> >> >> > > > -- > John Baldwin -- Vincenzo Maffione
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