Date: Sat, 1 May 2004 08:42:46 -0700 (PDT) From: Doug White <dwhite@gumbysoft.com> To: current@freebsd.org Subject: Re: src/sys/vm/vm_init.c v1.43 hangs amd64 Message-ID: <20040501082529.C80212@carver.gumbysoft.com> In-Reply-To: <20040430135155.C67990@carver.gumbysoft.com> References: <20040430135155.C67990@carver.gumbysoft.com>
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On Fri, 30 Apr 2004, Doug White wrote:
> I've been having problems with adm64 hanging under load on my dual opteron
> 244 machine. Its a HDAMA mainboard with 2GB RAM. The problems started
> around April 8. I finally found some time this week to narrow down the
> commit that causes the breakage; its rev 1.43 of src/sys/vm/vm_init.c.
Update to this.
1. Peter and I kicked this around on IRC yesterday. He wasn't able to
reproduce it with a separate program, at least immediately. We also did
some math and the numbers involved aren't large enough to be overflowing.
2. Changing COPTFLAGS to '-O -frename-registers -pipe' from the default
'-O2 -frename-registers -pipe' stops the crash. So it may be an
O2-specific optimization bug.
3. Assigning the values to a local variable doesn't seem to affect
things, although it allows for easier experimentation. Using this, I
found that the parentheses around the multiplications affects the
crash.
First, I added these variables:
vm_size_t nswbufsize;
vm_size_t nbufsize;
then later assigned them:
nbufsize = (nbuf*BKVASIZE);
nswbufsize = (nswbuf*MAXPHYS);
and changed the size argument to kmem_suballoc() to use the variables
instead of the expressions directly. This setup triggers the crash.
Removing the parentheses from the variable assignments:
nbufsize = nbuf*BKVASIZE;
nswbufsize = nswbuf*MAXPHYS;
stops the crash.
So in the end, at -O2, (nswbuf*MAXPHYS) != nswbuf*MAXPHYS. Creepy, eh?
I'll see if I can come up with a standalone test case to submit to the gcc
folks.
--
Doug White | FreeBSD: The Power to Serve
dwhite@gumbysoft.com | www.FreeBSD.org
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