Juha Saarinen wrote:
> fsstress filled up /usr 100% so I was going remove the p* directories
> and files. This provoked an oops:
> Kernel BUG at ll_rw_blk.c:700!
Ah. ll_rw_blk.c:700. I know it well.
My bet: A buffer was unmapped in block_flushpage() but somehow
somebody set it dirty again, and bdflush/kupdate tried to write
the thing out.
For ext3 I have implemented a "buffer tracing" mechanism. At
any interesting pointin the lifecycle of a buffer_head you
BUFFER_TRACE(bh, "some descriptive text")
then, thoughout the code I've added things like:
If the assertion fails you get a 64-slot backtrace of
all the buffer's state transitions. There's an example
output trace from when I was hitting exactly this same BUG()
at http://www.zip.com.au/~akpm/buffer-trace.txt - it's great.
See how journal_commit_transaction incorrectly sets the
buffer dirty and then flush_dirty_buffers grabs it.
I guess it's a bit late in XFS's development cycle to incorporate
something like this though.