Re: Bug in drivers/block/ll_rw_blk.c ?

[Livio Baldini Soares <livio@ime.usp.br>]

  Hi Yoav!

Yoav Weiss writes:
> A few days ago I posted the report attached below.  After some more
> research, I'm starting to think I've hit a bug in ll_rw_blk.c.
> 
> If the maintainer of the block dev subsystem happens to be reading
> this, please contact me on the list or by mail.

  I'm not the  maintainer, but I'm pretty sure that there  is no problem in
that specific  code... but I  think you're hitting  another bug in  the 2.4
tree (read below...)

[...snip...]

> The cloop (compressed loop) code I'm debugging is this one:
> 
> http://developer.linuxtag.net/knoppix/sources/cloop_1.0-2.tar.gz
> 
> I'm testing with kernel 2.4.22-rc2.

[...snip...]

> The stalled process waits on a page in mm/filemap.c:1505:
> 
> /* Again, try some read-ahead while waiting for the page to finish.. */
> 	generic_file_readahead(reada_ok, filp, inode, page);
> ------> wait_on_page(page);
> 
> 
> I found who wakes it up in calls that don't stall:
> unlock_page(), called from
> drivers/block/ll_rw_blk.c:end_that_request_first().
> bh->b_end_io(bh, uptodate) seems to do it.


  From  this description  it seems  that you  are hitting  a bug  which was
discussed to death here on the  list. Here's a thread with 143 messages for
you:

http://marc.theaimsgroup.com/?t=105400721000001&r=5&w=2

  And here are the threads in which a solution was dicussed:

http://marc.theaimsgroup.com/?t=105519528200001&r=1&w=2
http://marc.theaimsgroup.com/?t=105769525800005&r=3&w=2

  Notice, however, that  the patch Chris, Andrea, Jens  and others made for
this  problem is _already_  included in  2.4 (so,  yes, 2.4.22-rc2  has the
fix).

  So, you are  probably hitting the same bug, which was  not fixed 100%. If
you think  that your  test is  very easily reproducible  and can  shed more
light on this  problem, perhaps you should write to  Chris, Andrea and Jens
(with Cc: to the list), and show  them the test. I don't know if they would
be willing to spend more time  on this issue, specially with 2.6 around the
corner... 

  best regards,  

--  
  Livio B. Soares