Date: Mon, 19 Dec 2016 12:21:22 +0100 From: Vincenzo Maffione <v.maffione@gmail.com> To: Vincenzo Maffione <v.maffione@gmail.com>, Luigi Rizzo <luigi@freebsd.org>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Giuseppe Lettieri <g.lettieri@iet.unipi.it>, np@freebsd.com Subject: Re: cxgbe's native netmap support broken since r307394 Message-ID: <CA%2B_eA9jxs3FatSLs8fseb%2BJSrqWrYkegDHyKA1q2QH=Q4_LbJQ@mail.gmail.com> In-Reply-To: <20161217222812.GA4979@ox> References: <20161217222812.GA4979@ox>
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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
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