Date: Tue, 19 Jan 2010 15:02:31 -0500 From: Henry Wong <hwong@lumeta.com> To: freebsd-bugs@FreeBSD.org Cc: Henry Wong <hwong@lumeta.com> Subject: Re: kern/142728: Panic: Fatal trap 12 in g_io_request Message-ID: <4B560FD7.7050500@lumeta.com> In-Reply-To: <4B4D3DA3.1010706@lumeta.com> References: <201001120250.o0C2o2sI055242@freefall.freebsd.org> <4B4CCBCE.8040004@lumeta.com> <4B4D3DA3.1010706@lumeta.com>
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I have been able to narrow down this problem and have developed and partially tested a circumvention. The circumvention appears to be working. I found that there was a race condition that allowed a file system to possibly be mounted read-only more than once. With a certain sequence of mounting, mounting, retrieving, umounting and retrieving something different I was able to reproduce the problem. This problem can be considered as resolved as a duplicate of the problem Steve Hartland reported in April of 2008 in the freebsd-stable list: 7.0 panic in geom/ufs 7.0-RELEASE panic any ideas? except that it is still occurring in 8.0-RELEASE. The bottom line is that although FreeBSD 8.0 RELEASE allows a ufs filesystem to be mounted read-only multiple times, doing so will easily cause the system to panic trap with either a trap 12 or a trap 9 in g_io_request. The instruction that is causing the trap is where it is constructing the parametes for the g_trace. The particular parameter is pp->name. It appears that the pp pointer is referring to a page that is not in the address space. I have no idea whether the *cp from which the pp was retrieved is valid or not since each time this crashed for me, it either took no dump or hung after partially dumping. -- Henry Wong Lead Software Engineer Lumeta - / Securing the Network in the Face of Change / _hwong@lumeta.com_ 732.357.3534 (office) 732.564.0731 (fax) 220 Davidson Avenue Somerset , NJ 08873-4146 www.lumeta.com
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