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From: Robert Watson <rwatson@FreeBSD.ORG>
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To: Willem Jan Withagen <wjw@withagen.nl>
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Subject: Re: Fatal LOR: PV ENTRY (UMA zone) @
	/home2/src/sys/vm/uma_core.c:2033
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On Wed, 28 Jul 2004, Willem Jan Withagen wrote:

> Running on amd64:
> 
<snip>
<unsnip> 
> And right followed by....
> 
> panic: lock (sleep mutex) Giant not locked @ /home2/src/sys/kern/vfs_syscalls.c:
> 959
> cpuid = 0;
> KDB: stack backtrace:
> kdb_backtrace() at kdb_backtrace+0x34
> panic() at panic+0x1d2
> witness_unlock() at witness_unlock+0xdd
> _mtx_unlock_flags() at _mtx_unlock_flags+0x68
> kern_open() at kern_open+0x128
> open() at open+0x18
> syscall() at syscall+0x330
> Xfast_syscall() at Xfast_syscall+0xa8
> --- syscall (5, FreeBSD ELF64, open), rip = 0x76d75c, rsp = 0x7fffffffe088, rbp
> = 0x7fffffffe0c0 ---
> KDB: enter: panic
> [thread 100316]
> Stopped at      kdb_enter+0x2e: nop

I've seen several reports of "mysterious" panics where Giant isn't held on
return from namei() or other points following a name lookup.  Kris
Kenneway reported this on the package build cluster, for example.  I'm
wondering if something handling a page fault hit by namei() during a
string copy in from user space if resulting in Giant not being held where
it should be.  In Kris's case, we tried pushing around GIANT_REQUIRED some
because I thought maybe the caller wasn't holding Giant when it should,
but that turned out not to be it.  So maybe we have some sort of
preemption/VM/locking issue? 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Principal Research Scientist, McAfee Research