bogus b_data pointer?

[Can Sar <csar@xxxxxxxxxxxx>]

Hi,

I've instrumented the mark_buffer_dirty routine of the kernel to print 
the address that b_data points to for a simple block device driver I 
got from http://lwn.net/Articles/58720/. I get perfectly valid 
addresses most of the time, except that sometimes the pointer has the 
value of 0x400. I have been looking at this for a very long time and I 
have no idea what could be causing this?
Does anyone have any ideas?

This happens in kernel 2.6.11 on ext3.

Thanks for any help,
Can


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