Date: Sun, 11 Oct 2009 12:26:31 -0700 From: Harsha Srinath <inpcb.harsha@gmail.com> To: net@freebsd.org, freebsd-current@freebsd.org Subject: Page fault in IFNET_WLOCK_ASSERT [if.c and pccbb.c] Message-ID: <e1b1c5880910111226o65e0d1a9va975f4cd837271bb@mail.gmail.com>
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Hi all, I'm running an updated HEAD kernel and got a page fault in ifindex_alloc_locked() in if.c. I figured that the problem was caused by the (pluggable) network card of my laptop and found that during the initialization of the interface, cb_event_thread() takes the giant lock and up the call chain in if_alloc(), we call IFNET_WLOCK() and assert on the RW locks in ifindex_alloc_locked(). It is in the asset macro IFNET_WLOCK_ASSERT() I see the page fault. I looked up some recent related changes and noticed the following comment in one of the check-ins in- http://svn.freebsd.org/viewvc/base/head/sys/net/if.c "Break out allocation of new ifindex values from if_alloc() and if_vmove(), and centralize in a single function ifindex_alloc(). Assert the IFNET_WLOCK, and add missing IFNET_WLOCK in if_alloc(). This does not close all known races in this code." So I think I have hit one of those fault conditions. Apparently the giant lock code was removed and added back recently - http://svn.freebsd.org/viewvc/base/head/sys/dev/pccbb/pccbb.c I believe that the root cause is that ifnet_rw is a non sleepable exclusive RW lock and we have taken the exclusive sleep mutex Giant before that. Any pointers and suggestions are welcome. Many thanks, Harsha
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