Date: Fri, 21 Feb 2003 11:09:13 -0800 (PST) From: Ed Alley <alley1@llnl.gov> To: freebsd-hackers@freebsd.org Subject: Some advice in analyzing vfs crashes Message-ID: <200302211909.h1LJ9Doc036666@jordan.llnl.gov>
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I am looking for advice:
I am developing a file system (it can exist as a module or compiled in).
A problem has developed which I do not know how to debug and would like
some advice.
The symptoms:
I can mount my FS read from it, write into and out of it and unmount
it. However, it is subject to periodic page-faults. These can happen while
the FS is mounted, or after it has been dismounted (even for a while).
The page-fault occurs at random and doesn't depend on whether I reference
the FS or not. When I look at the core dump, I see that it occurs in
the VFS usually after an open, say ufs_open(), and often in vn_isdisk().
When I look at the arguments to these calls, I see *vp = 0 or a bad address.
Clearly my FS has corrupted a vnode, or the buffer cache.
(Maybe some vnodes are still locked or referenced, or corrupted? or some
buffer blocks are corrupted or not released?)
So I'm thinking to do the following:
1. Mount my FS, cd into it and do the following:
cp /etc/passwd .
rm *
cd /
umount /mnt
2. panic the system to get a core dump.
This could be done, say, by putting the panic(9) call
in my vfs unmount() function before the return.
My questions:
Is there a way to analyize a core dump with gdb(1) and detect:
a) corrupted vnodes?
b) locked/referenced vnodes (that should have been released)?
c) corrupted buffer cache?
d) locked buffer blocks (that should have been released)?
In other words, I want evaluate the state of the vfs after my
FS has done its damage, but before the inevitable panic occurs.
Any further hints on what I should look at would be greatly appreciated.
Thank-you
Ed Alley
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