LOR in /usr/src/sys/netinet/in.c:972

John Baldwin jhb at FreeBSD.org
Thu Sep 15 11:21:03 PDT 2005

On Saturday 03 September 2005 10:28 am, Dan Cojocar wrote:
> Hello,
> Here is my second lor for today :) that i didn't find on
> http://sources.zabbadoz.net/freebsd/lor.html
> I get this when i run dhclient on cdce0 interface. It's harmless, because I
> obtain an valid ip and everything is working ok.
> lock order reversal
> 1st 0xc06a2e40 in_multi_mtx (in_multi_mtx) @ /usr/src/sys/netinet/in.c:972
> 2nd 0xc0655660 Giant (Giant) @ /usr/src/sys/net/if.c:1998
> KDB: stack backtrace:
> witness_checkorder(c0655660,9,c0612eef,7ce,12c) at witness_checkorder+0x51c
> _mtx_lock_flags(c0655660,0,c0612eef,7ce,c) at _mtx_lock_flags+0x54
> if_addmulti(c1a67800,d5729afc,d5729af8,3cc,c1bf0780) at if_addmulti+0x260
> in_addmulti(d5729b40,c1a67800,1,2cc,c1b8bbc8) at in_addmulti+0x66
> in_ifinit(c1f53190,0,0,0,d5729b90) at in_ifinit+0x5bc
> in_control(c1f8b000,8040691a,c1f53180,c1a67800,c1aa0e10) at
> in_control+0xfaa ifioctl(c1f8b000,8040691a,c1f53180,c1aa0e10,2) at
> ifioctl+0x15a
> soo_ioctl(c1f5e000,8040691a,c1f53180,c1f65200,c1aa0e10) at soo_ioctl+0x2e8
> ioctl(c1aa0e10,d5729d04,c,422,3) at ioctl+0x118
> syscall(3b,3b,3b,808e3a0,0) at syscall+0x13d
> Xint0x80_syscall() at Xint0x80_syscall+0x1f
> --- syscall (54, FreeBSD ELF32, ioctl), eip = 0x807f49b, esp = 0xbfbfe5bc,
> ebp = 0xbfbfee28 ---

This is a real LOR caused by the fact that in_addmulti() holds the 
in_multi_mtx() lock across the call to if_addmulti() and if_addmulti() will 
acquire Giant for non-MPsafe drivers around calls into their ioctl routine.  
I think that to better expose these issues, the various conditional-Giant 
macros need to include a witness_warn() to make sure only sleepable locks 
and/or Giant are held when the lock macro is invoked.

John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org

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