Re: ext3 deadlock?

[Andrew Morton <akpm@zip.com.au>]

Paul Mackerras wrote:
> 
> I'm having a problem with 2.5.15 on an old slow powerbook 3400.  It
> gets stuck during boot at the point where it starts syslogd.  At that
> point show_state() reveals that kjournald and one of the two syslogd
> processes are stuck in D state.  The stack trace for kjournald is:
> 
> schedule
> __wait_on_buffer
> journal_commit_transaction
> kjournald

kjournald is actually running a commit.  So recovery was successful
and the filesystem is up and running.

It's this trace which is the problem.  All the other processes
are blocked by kjournald.

kjournald is pretty much write-only.  It will perform the
occasional read to load the indirect blocks which describe the
journal location.  But that would show a different backtrace.

It appears that kjournald has submitted a block for writeout
(via submit_bh() or ll_rw_block()) and the interrupt which
signifies completion simply hasn't happened.

> ...
> 
> Can anyone suggest where I could start looking to work out why
> kjournald is getting stuck in __wait_on_buffer?  Where in the code
> does the corresponding wakeup happen?

journal_commit_transaction() writes blocks from several different
places, via ll_rw_block() or submit_bh().  It waits for the
buffers to come unlocked in the end_buffer_io_sync() or
journal_end_buffer_io_sync() completion handlers.

Possibly the device driver has failed to deliver an interrupt.

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